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ScrollView.javaAPI DocAndroid 1.5 API44383Wed May 06 22:41:56 BST 2009android.widget

ScrollView

public class ScrollView extends FrameLayout
Layout container for a view hierarchy that can be scrolled by the user, allowing it to be larger than the physical display. A ScrollView is a {@link FrameLayout}, meaning you should place one child in it containing the entire contents to scroll; this child may itself be a layout manager with a complex hierarchy of objects. A child that is often used is a {@link LinearLayout} in a vertical orientation, presenting a vertical array of top-level items that the user can scroll through.

The {@link TextView} class also takes care of its own scrolling, so does not require a ScrollView, but using the two together is possible to achieve the effect of a text view within a larger container.

ScrollView only supports vertical scrolling.

Fields Summary
static final String
TAG
static final boolean
localLOGV
static final int
ANIMATED_SCROLL_GAP
static final float
MAX_SCROLL_FACTOR
private long
mLastScroll
private final android.graphics.Rect
mTempRect
private Scroller
mScroller
private boolean
mScrollViewMovedFocus
Flag to indicate that we are moving focus ourselves. This is so the code that watches for focus changes initiated outside this ScrollView knows that it does not have to do anything.
private float
mLastMotionY
Position of the last motion event.
private boolean
mIsLayoutDirty
True when the layout has changed but the traversal has not come through yet. Ideally the view hierarchy would keep track of this for us.
private android.view.View
mChildToScrollTo
The child to give focus to in the event that a child has requested focus while the layout is dirty. This prevents the scroll from being wrong if the child has not been laid out before requesting focus.
private boolean
mIsBeingDragged
True if the user is currently dragging this ScrollView around. This is not the same as 'is being flinged', which can be checked by mScroller.isFinished() (flinging begins when the user lifts his finger).
private android.view.VelocityTracker
mVelocityTracker
Determines speed during touch scrolling
private boolean
mFillViewport
When set to true, the scroll view measure its child to make it fill the currently visible area.
private boolean
mSmoothScrollingEnabled
Whether arrow scrolling is animated.
private int
mTouchSlop
Constructors Summary
public ScrollView(android.content.Context context)


       
        this(context, null);
public ScrollView(android.content.Context context, android.util.AttributeSet attrs)

        this(context, attrs, com.android.internal.R.attr.scrollViewStyle);
public ScrollView(android.content.Context context, android.util.AttributeSet attrs, int defStyle)

        super(context, attrs, defStyle);
        initScrollView();

        TypedArray a =
            context.obtainStyledAttributes(attrs, com.android.internal.R.styleable.ScrollView, defStyle, 0);

        setFillViewport(a.getBoolean(R.styleable.ScrollView_fillViewport, false));

        a.recycle();
Methods Summary
public voidaddView(android.view.View child, ViewGroup.LayoutParams params)

        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child, params);
public voidaddView(android.view.View child, int index, ViewGroup.LayoutParams params)

        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child, index, params);
public voidaddView(android.view.View child)

        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child);
public voidaddView(android.view.View child, int index)

        if (getChildCount() > 0) {
            throw new IllegalStateException("ScrollView can host only one direct child");
        }

        super.addView(child, index);
public booleanarrowScroll(int direction)
Handle scrolling in response to an up or down arrow click.

param
direction The direction corresponding to the arrow key that was pressed
return
True if we consumed the event, false otherwise


        View currentFocused = findFocus();
        if (currentFocused == this) currentFocused = null;

        View nextFocused = FocusFinder.getInstance().findNextFocus(this, currentFocused, direction);

        final int maxJump = getMaxScrollAmount();

        if (nextFocused != null && isWithinDeltaOfScreen(nextFocused, maxJump)) {
            nextFocused.getDrawingRect(mTempRect);
            offsetDescendantRectToMyCoords(nextFocused, mTempRect);
            int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
            doScrollY(scrollDelta);
            nextFocused.requestFocus(direction);
        } else {
            // no new focus
            int scrollDelta = maxJump;

            if (direction == View.FOCUS_UP && getScrollY() < scrollDelta) {
                scrollDelta = getScrollY();
            } else if (direction == View.FOCUS_DOWN) {

                int daBottom = getChildAt(getChildCount() - 1).getBottom();

                int screenBottom = getScrollY() + getHeight();

                if (daBottom - screenBottom < maxJump) {
                    scrollDelta = daBottom - screenBottom;
                }
            }
            if (scrollDelta == 0) {
                return false;
            }
            doScrollY(direction == View.FOCUS_DOWN ? scrollDelta : -scrollDelta);
        }

        if (currentFocused != null && currentFocused.isFocused()
                && isOffScreen(currentFocused)) {
            // previously focused item still has focus and is off screen, give
            // it up (take it back to ourselves)
            // (also, need to temporarily force FOCUS_BEFORE_DESCENDANTS so we are
            // sure to
            // get it)
            final int descendantFocusability = getDescendantFocusability();  // save
            setDescendantFocusability(ViewGroup.FOCUS_BEFORE_DESCENDANTS);
            requestFocus();
            setDescendantFocusability(descendantFocusability);  // restore
        }
        return true;
private booleancanScroll()

return
Returns true this ScrollView can be scrolled

        View child = getChildAt(0);
        if (child != null) {
            int childHeight = child.getHeight();
            return getHeight() < childHeight + mPaddingTop + mPaddingBottom;
        }
        return false;
private intclamp(int n, int my, int child)

        if (my >= child || n < 0) {
            /* my >= child is this case:
             *                    |--------------- me ---------------|
             *     |------ child ------|
             * or
             *     |--------------- me ---------------|
             *            |------ child ------|
             * or
             *     |--------------- me ---------------|
             *                                  |------ child ------|
             *
             * n < 0 is this case:
             *     |------ me ------|
             *                    |-------- child --------|
             *     |-- mScrollX --|
             */
            return 0;
        }
        if ((my+n) > child) {
            /* this case:
             *                    |------ me ------|
             *     |------ child ------|
             *     |-- mScrollX --|
             */
            return child-my;
        }
        return n;
public voidcomputeScroll()

        if (mScroller.computeScrollOffset()) {
            // This is called at drawing time by ViewGroup.  We don't want to
            // re-show the scrollbars at this point, which scrollTo will do,
            // so we replicate most of scrollTo here.
            //
            //         It's a little odd to call onScrollChanged from inside the drawing.
            //
            //         It is, except when you remember that computeScroll() is used to
            //         animate scrolling. So unless we want to defer the onScrollChanged()
            //         until the end of the animated scrolling, we don't really have a
            //         choice here.
            //
            //         I agree.  The alternative, which I think would be worse, is to post
            //         something and tell the subclasses later.  This is bad because there
            //         will be a window where mScrollX/Y is different from what the app
            //         thinks it is.
            //
            int oldX = mScrollX;
            int oldY = mScrollY;
            int x = mScroller.getCurrX();
            int y = mScroller.getCurrY();
            if (getChildCount() > 0) {
                View child = getChildAt(0);
                mScrollX = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
                mScrollY = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
                if (localLOGV) Log.v(TAG, "mScrollY=" + mScrollY + " y=" + y
                        + " height=" + this.getHeight()
                        + " child height=" + child.getHeight());
            } else {
                mScrollX = x;
                mScrollY = y;
            }            
            if (oldX != mScrollX || oldY != mScrollY) {
                onScrollChanged(mScrollX, mScrollY, oldX, oldY);
            }
            
            // Keep on drawing until the animation has finished.
            postInvalidate();
        }
protected intcomputeScrollDeltaToGetChildRectOnScreen(android.graphics.Rect rect)
Compute the amount to scroll in the Y direction in order to get a rectangle completely on the screen (or, if taller than the screen, at least the first screen size chunk of it).

param
rect The rect.
return
The scroll delta.


        int height = getHeight();
        int screenTop = getScrollY();
        int screenBottom = screenTop + height;

        int fadingEdge = getVerticalFadingEdgeLength();

        // leave room for top fading edge as long as rect isn't at very top
        if (rect.top > 0) {
            screenTop += fadingEdge;
        }

        // leave room for bottom fading edge as long as rect isn't at very bottom
        if (rect.bottom < getChildAt(0).getHeight()) {
            screenBottom -= fadingEdge;
        }

        int scrollYDelta = 0;

        if (localLOGV) Log.v(TAG, "child=" + rect.toShortString()
                + " screenTop=" + screenTop + " screenBottom=" + screenBottom
                + " height=" + height);
        if (rect.bottom > screenBottom && rect.top > screenTop) {
            // need to move down to get it in view: move down just enough so
            // that the entire rectangle is in view (or at least the first
            // screen size chunk).

            if (rect.height() > height) {
                // just enough to get screen size chunk on
                scrollYDelta += (rect.top - screenTop);
            } else {
                // get entire rect at bottom of screen
                scrollYDelta += (rect.bottom - screenBottom);
            }

            // make sure we aren't scrolling beyond the end of our content
            int bottom = getChildAt(getChildCount() - 1).getBottom();
            int distanceToBottom = bottom - screenBottom;
            if (localLOGV) Log.v(TAG, "scrollYDelta=" + scrollYDelta
                    + " distanceToBottom=" + distanceToBottom);
            scrollYDelta = Math.min(scrollYDelta, distanceToBottom);

        } else if (rect.top < screenTop && rect.bottom < screenBottom) {
            // need to move up to get it in view: move up just enough so that
            // entire rectangle is in view (or at least the first screen
            // size chunk of it).

            if (rect.height() > height) {
                // screen size chunk
                scrollYDelta -= (screenBottom - rect.bottom);
            } else {
                // entire rect at top
                scrollYDelta -= (screenTop - rect.top);
            }

            // make sure we aren't scrolling any further than the top our content
            scrollYDelta = Math.max(scrollYDelta, -getScrollY());
        }
        return scrollYDelta;
protected intcomputeVerticalScrollRange()

The scroll range of a scroll view is the overall height of all of its children.

        int count = getChildCount();
        return count == 0 ? getHeight() : (getChildAt(0)).getBottom();
public booleandispatchKeyEvent(android.view.KeyEvent event)

        // Let the focused view and/or our descendants get the key first
        boolean handled = super.dispatchKeyEvent(event);
        if (handled) {
            return true;
        }
        return executeKeyEvent(event);
private voiddoScrollY(int delta)
Smooth scroll by a Y delta

param
delta the number of pixels to scroll by on the Y axis

        if (delta != 0) {
            if (mSmoothScrollingEnabled) {
                smoothScrollBy(0, delta);
            } else {
                scrollBy(0, delta);
            }
        }
public booleanexecuteKeyEvent(android.view.KeyEvent event)
You can call this function yourself to have the scroll view perform scrolling from a key event, just as if the event had been dispatched to it by the view hierarchy.

param
event The key event to execute.
return
Return true if the event was handled, else false.

        mTempRect.setEmpty();

        if (!canScroll()) {
            if (isFocused()) {
                View currentFocused = findFocus();
                if (currentFocused == this) currentFocused = null;
                View nextFocused = FocusFinder.getInstance().findNextFocus(this,
                        currentFocused, View.FOCUS_DOWN);
                return nextFocused != null
                        && nextFocused != this
                        && nextFocused.requestFocus(View.FOCUS_DOWN);
            }
            return false;
        }

        boolean handled = false;
        if (event.getAction() == KeyEvent.ACTION_DOWN) {
            switch (event.getKeyCode()) {
                case KeyEvent.KEYCODE_DPAD_UP:
                    if (!event.isAltPressed()) {
                        handled = arrowScroll(View.FOCUS_UP);
                    } else {
                        handled = fullScroll(View.FOCUS_UP);
                    }
                    break;
                case KeyEvent.KEYCODE_DPAD_DOWN:
                    if (!event.isAltPressed()) {
                        handled = arrowScroll(View.FOCUS_DOWN);
                    } else {
                        handled = fullScroll(View.FOCUS_DOWN);
                    }
                    break;
                case KeyEvent.KEYCODE_SPACE:
                    pageScroll(event.isShiftPressed() ? View.FOCUS_UP : View.FOCUS_DOWN);
                    break;
            }
        }

        return handled;
private android.view.ViewfindFocusableViewInBounds(boolean topFocus, int top, int bottom)

Finds the next focusable component that fits in the specified bounds.

param
topFocus look for a candidate is the one at the top of the bounds if topFocus is true, or at the bottom of the bounds if topFocus is false
param
top the top offset of the bounds in which a focusable must be found
param
bottom the bottom offset of the bounds in which a focusable must be found
return
the next focusable component in the bounds or null if none can be found


        List<View> focusables = getFocusables(View.FOCUS_FORWARD);
        View focusCandidate = null;

        /*
         * A fully contained focusable is one where its top is below the bound's
         * top, and its bottom is above the bound's bottom. A partially
         * contained focusable is one where some part of it is within the
         * bounds, but it also has some part that is not within bounds.  A fully contained
         * focusable is preferred to a partially contained focusable.
         */
        boolean foundFullyContainedFocusable = false;

        int count = focusables.size();
        for (int i = 0; i < count; i++) {
            View view = focusables.get(i);
            int viewTop = view.getTop();
            int viewBottom = view.getBottom();

            if (top < viewBottom && viewTop < bottom) {
                /*
                 * the focusable is in the target area, it is a candidate for
                 * focusing
                 */

                final boolean viewIsFullyContained = (top < viewTop) &&
                        (viewBottom < bottom);

                if (focusCandidate == null) {
                    /* No candidate, take this one */
                    focusCandidate = view;
                    foundFullyContainedFocusable = viewIsFullyContained;
                } else {
                    final boolean viewIsCloserToBoundary =
                            (topFocus && viewTop < focusCandidate.getTop()) ||
                                    (!topFocus && viewBottom > focusCandidate
                                            .getBottom());

                    if (foundFullyContainedFocusable) {
                        if (viewIsFullyContained && viewIsCloserToBoundary) {
                            /*
                             * We're dealing with only fully contained views, so
                             * it has to be closer to the boundary to beat our
                             * candidate
                             */
                            focusCandidate = view;
                        }
                    } else {
                        if (viewIsFullyContained) {
                            /* Any fully contained view beats a partially contained view */
                            focusCandidate = view;
                            foundFullyContainedFocusable = true;
                        } else if (viewIsCloserToBoundary) {
                            /*
                             * Partially contained view beats another partially
                             * contained view if it's closer
                             */
                            focusCandidate = view;
                        }
                    }
                }
            }
        }

        return focusCandidate;
private android.view.ViewfindFocusableViewInMyBounds(boolean topFocus, int top, android.view.View preferredFocusable)

Finds the next focusable component that fits in this View's bounds (excluding fading edges) pretending that this View's top is located at the parameter top.

param
topFocus look for a candidate is the one at the top of the bounds if topFocus is true, or at the bottom of the bounds if topFocus is false
param
top the top offset of the bounds in which a focusable must be found (the fading edge is assumed to start at this position)
param
preferredFocusable the View that has highest priority and will be returned if it is within my bounds (null is valid)
return
the next focusable component in the bounds or null if none can be found

        /*
         * The fading edge's transparent side should be considered for focus
         * since it's mostly visible, so we divide the actual fading edge length
         * by 2.
         */
        final int fadingEdgeLength = getVerticalFadingEdgeLength() / 2;
        final int topWithoutFadingEdge = top + fadingEdgeLength;
        final int bottomWithoutFadingEdge = top + getHeight() - fadingEdgeLength;

        if ((preferredFocusable != null)
                && (preferredFocusable.getTop() < bottomWithoutFadingEdge)
                && (preferredFocusable.getBottom() > topWithoutFadingEdge)) {
            return preferredFocusable;
        }

        return findFocusableViewInBounds(topFocus, topWithoutFadingEdge,
                bottomWithoutFadingEdge);
public voidfling(int velocityY)
Fling the scroll view

param
velocityY The initial velocity in the Y direction. Positive numbers mean that the finger/curor is moving down the screen, which means we want to scroll towards the top.

        int height = getHeight() - mPaddingBottom - mPaddingTop;
        int bottom = getChildAt(0).getHeight();

        mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, bottom - height);

        final boolean movingDown = velocityY > 0;

        View newFocused =
                findFocusableViewInMyBounds(movingDown, mScroller.getFinalY(), findFocus());
        if (newFocused == null) {
            newFocused = this;
        }

        if (newFocused != findFocus()
                && newFocused.requestFocus(movingDown ? View.FOCUS_DOWN : View.FOCUS_UP)) {
            mScrollViewMovedFocus = true;
            mScrollViewMovedFocus = false;
        }

        invalidate();
public booleanfullScroll(int direction)

Handles scrolling in response to a "home/end" shortcut press. This method will scroll the view to the top or bottom and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.

param
direction the scroll direction: {@link android.view.View#FOCUS_UP} to go the top of the view or {@link android.view.View#FOCUS_DOWN} to go the bottom
return
true if the key event is consumed by this method, false otherwise

        boolean down = direction == View.FOCUS_DOWN;
        int height = getHeight();

        mTempRect.top = 0;
        mTempRect.bottom = height;

        if (down) {
            int count = getChildCount();
            if (count > 0) {
                View view = getChildAt(count - 1);
                mTempRect.bottom = view.getBottom();
                mTempRect.top = mTempRect.bottom - height;
            }
        }

        return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
protected floatgetBottomFadingEdgeStrength()

        if (getChildCount() == 0) {
            return 0.0f;
        }

        final int length = getVerticalFadingEdgeLength();
        final int bottomEdge = getHeight() - mPaddingBottom;
        final int span = getChildAt(0).getBottom() - mScrollY - bottomEdge;
        if (span < length) {
            return span / (float) length;
        }

        return 1.0f;
public intgetMaxScrollAmount()

return
The maximum amount this scroll view will scroll in response to an arrow event.

        return (int) (MAX_SCROLL_FACTOR * (mBottom - mTop));
protected floatgetTopFadingEdgeStrength()

        if (getChildCount() == 0) {
            return 0.0f;
        }

        final int length = getVerticalFadingEdgeLength();
        if (mScrollY < length) {
            return mScrollY / (float) length;
        }

        return 1.0f;
private voidinitScrollView()

        mScroller = new Scroller(getContext());
        setFocusable(true);
        setDescendantFocusability(FOCUS_AFTER_DESCENDANTS);
        setWillNotDraw(false);
        mTouchSlop = ViewConfiguration.get(getContext()).getScaledTouchSlop();
public booleanisFillViewport()
Indicates whether this ScrollView's content is stretched to fill the viewport.

return
True if the content fills the viewport, false otherwise.

        return mFillViewport;
private booleanisOffScreen(android.view.View descendant)

return
whether the descendant of this scroll view is scrolled off screen.

        return !isWithinDeltaOfScreen(descendant, 0);
public booleanisSmoothScrollingEnabled()

return
Whether arrow scrolling will animate its transition.

        return mSmoothScrollingEnabled;
private booleanisViewDescendantOf(android.view.View child, android.view.View parent)
Return true if child is an descendant of parent, (or equal to the parent).

        if (child == parent) {
            return true;
        }

        final ViewParent theParent = child.getParent();
        return (theParent instanceof ViewGroup) && isViewDescendantOf((View) theParent, parent);
private booleanisWithinDeltaOfScreen(android.view.View descendant, int delta)

return
whether the descendant of this scroll view is within delta pixels of being on the screen.

        descendant.getDrawingRect(mTempRect);
        offsetDescendantRectToMyCoords(descendant, mTempRect);

        return (mTempRect.bottom + delta) >= getScrollY()
                && (mTempRect.top - delta) <= (getScrollY() + getHeight());
protected voidmeasureChild(android.view.View child, int parentWidthMeasureSpec, int parentHeightMeasureSpec)

        ViewGroup.LayoutParams lp = child.getLayoutParams();

        int childWidthMeasureSpec;
        int childHeightMeasureSpec;

        childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec, mPaddingLeft
                + mPaddingRight, lp.width);

        childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(0, MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
protected voidmeasureChildWithMargins(android.view.View child, int parentWidthMeasureSpec, int widthUsed, int parentHeightMeasureSpec, int heightUsed)

        final MarginLayoutParams lp = (MarginLayoutParams) child.getLayoutParams();

        final int childWidthMeasureSpec = getChildMeasureSpec(parentWidthMeasureSpec,
                mPaddingLeft + mPaddingRight + lp.leftMargin + lp.rightMargin
                        + widthUsed, lp.width);
        final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(
                lp.topMargin + lp.bottomMargin, MeasureSpec.UNSPECIFIED);

        child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
public booleanonInterceptTouchEvent(android.view.MotionEvent ev)

        /*
         * This method JUST determines whether we want to intercept the motion.
         * If we return true, onMotionEvent will be called and we do the actual
         * scrolling there.
         */

        /*
        * Shortcut the most recurring case: the user is in the dragging
        * state and he is moving his finger.  We want to intercept this
        * motion.
        */
        final int action = ev.getAction();
        if ((action == MotionEvent.ACTION_MOVE) && (mIsBeingDragged)) {
            return true;
        }

        if (!canScroll()) {
            mIsBeingDragged = false;
            return false;
        }

        final float y = ev.getY();

        switch (action) {
            case MotionEvent.ACTION_MOVE:
                /*
                 * mIsBeingDragged == false, otherwise the shortcut would have caught it. Check
                 * whether the user has moved far enough from his original down touch.
                 */

                /*
                * Locally do absolute value. mLastMotionY is set to the y value
                * of the down event.
                */
                final int yDiff = (int) Math.abs(y - mLastMotionY);
                if (yDiff > mTouchSlop) {
                    mIsBeingDragged = true;
                }
                break;

            case MotionEvent.ACTION_DOWN:
                /* Remember location of down touch */
                mLastMotionY = y;

                /*
                * If being flinged and user touches the screen, initiate drag;
                * otherwise don't.  mScroller.isFinished should be false when
                * being flinged.
                */
                mIsBeingDragged = !mScroller.isFinished();
                break;

            case MotionEvent.ACTION_CANCEL:
            case MotionEvent.ACTION_UP:
                /* Release the drag */
                mIsBeingDragged = false;
                break;
        }

        /*
        * The only time we want to intercept motion events is if we are in the
        * drag mode.
        */
        return mIsBeingDragged;
protected voidonLayout(boolean changed, int l, int t, int r, int b)

        super.onLayout(changed, l, t, r, b);
        mIsLayoutDirty = false;
        // Give a child focus if it needs it 
        if (mChildToScrollTo != null && isViewDescendantOf(mChildToScrollTo, this)) {
                scrollToChild(mChildToScrollTo);
        }
        mChildToScrollTo = null;

        // Calling this with the present values causes it to re-clam them
        scrollTo(mScrollX, mScrollY);
protected voidonMeasure(int widthMeasureSpec, int heightMeasureSpec)

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        if (!mFillViewport) {
            return;
        }

        final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
        if (heightMode == MeasureSpec.UNSPECIFIED) {
            return;
        }

        final View child = getChildAt(0);
        int height = getMeasuredHeight();
        if (child.getMeasuredHeight() < height) {
            final FrameLayout.LayoutParams lp = (LayoutParams) child.getLayoutParams();

            int childWidthMeasureSpec = getChildMeasureSpec(widthMeasureSpec, mPaddingLeft
                    + mPaddingRight, lp.width);
            height -= mPaddingTop;
            height -= mPaddingBottom;
            int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY);

            child.measure(childWidthMeasureSpec, childHeightMeasureSpec);
        }
protected booleanonRequestFocusInDescendants(int direction, android.graphics.Rect previouslyFocusedRect)
When looking for focus in children of a scroll view, need to be a little more careful not to give focus to something that is scrolled off screen. This is more expensive than the default {@link android.view.ViewGroup} implementation, otherwise this behavior might have been made the default.


        // convert from forward / backward notation to up / down / left / right
        // (ugh).
        if (direction == View.FOCUS_FORWARD) {
            direction = View.FOCUS_DOWN;
        } else if (direction == View.FOCUS_BACKWARD) {
            direction = View.FOCUS_UP;
        }

        final View nextFocus = previouslyFocusedRect == null ?
                FocusFinder.getInstance().findNextFocus(this, null, direction) :
                FocusFinder.getInstance().findNextFocusFromRect(this,
                        previouslyFocusedRect, direction);

        if (nextFocus == null) {
            return false;
        }

        if (isOffScreen(nextFocus)) {
            return false;
        }

        return nextFocus.requestFocus(direction, previouslyFocusedRect);
protected voidonSizeChanged(int w, int h, int oldw, int oldh)

        super.onSizeChanged(w, h, oldw, oldh);

        View currentFocused = findFocus();
        if (null == currentFocused || this == currentFocused)
            return;

        final int maxJump = mBottom - mTop;

        if (isWithinDeltaOfScreen(currentFocused, maxJump)) {
            currentFocused.getDrawingRect(mTempRect);
            offsetDescendantRectToMyCoords(currentFocused, mTempRect);
            int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);
            doScrollY(scrollDelta);
        }
public booleanonTouchEvent(android.view.MotionEvent ev)


        if (ev.getAction() == MotionEvent.ACTION_DOWN && ev.getEdgeFlags() != 0) {
            // Don't handle edge touches immediately -- they may actually belong to one of our
            // descendants.
            return false;
        }
        
        if (!canScroll()) {
            return false;
        }

        if (mVelocityTracker == null) {
            mVelocityTracker = VelocityTracker.obtain();
        }
        mVelocityTracker.addMovement(ev);

        final int action = ev.getAction();
        final float y = ev.getY();

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                /*
                * If being flinged and user touches, stop the fling. isFinished
                * will be false if being flinged.
                */
                if (!mScroller.isFinished()) {
                    mScroller.abortAnimation();
                }

                // Remember where the motion event started
                mLastMotionY = y;
                break;
            case MotionEvent.ACTION_MOVE:
                // Scroll to follow the motion event
                final int deltaY = (int) (mLastMotionY - y);
                mLastMotionY = y;

                if (deltaY < 0) {
                    if (mScrollY > 0) {
                        scrollBy(0, deltaY);
                    }
                } else if (deltaY > 0) {
                    final int bottomEdge = getHeight() - mPaddingBottom;
                    final int availableToScroll = getChildAt(0).getBottom() - mScrollY - bottomEdge;
                    if (availableToScroll > 0) {
                        scrollBy(0, Math.min(availableToScroll, deltaY));
                    }
                }
                break;
            case MotionEvent.ACTION_UP:
                final VelocityTracker velocityTracker = mVelocityTracker;
                velocityTracker.computeCurrentVelocity(1000);
                int initialVelocity = (int) velocityTracker.getYVelocity();

                if ((Math.abs(initialVelocity) >
                        ViewConfiguration.get(mContext).getScaledMinimumFlingVelocity()) &&
                        getChildCount() > 0) {
                    fling(-initialVelocity);
                }

                if (mVelocityTracker != null) {
                    mVelocityTracker.recycle();
                    mVelocityTracker = null;
                }
        }
        return true;
public booleanpageScroll(int direction)

Handles scrolling in response to a "page up/down" shortcut press. This method will scroll the view by one page up or down and give the focus to the topmost/bottommost component in the new visible area. If no component is a good candidate for focus, this scrollview reclaims the focus.

param
direction the scroll direction: {@link android.view.View#FOCUS_UP} to go one page up or {@link android.view.View#FOCUS_DOWN} to go one page down
return
true if the key event is consumed by this method, false otherwise

        boolean down = direction == View.FOCUS_DOWN;
        int height = getHeight();

        if (down) {
            mTempRect.top = getScrollY() + height;
            int count = getChildCount();
            if (count > 0) {
                View view = getChildAt(count - 1);
                if (mTempRect.top + height > view.getBottom()) {
                    mTempRect.top = view.getBottom() - height;
                }
            }
        } else {
            mTempRect.top = getScrollY() - height;
            if (mTempRect.top < 0) {
                mTempRect.top = 0;
            }
        }
        mTempRect.bottom = mTempRect.top + height;

        return scrollAndFocus(direction, mTempRect.top, mTempRect.bottom);
public voidrequestChildFocus(android.view.View child, android.view.View focused)

        if (!mScrollViewMovedFocus) {
            if (!mIsLayoutDirty) {
                scrollToChild(focused);
            } else {
                // The child may not be laid out yet, we can't compute the scroll yet
                mChildToScrollTo = focused;
            }
        }
        super.requestChildFocus(child, focused);
public booleanrequestChildRectangleOnScreen(android.view.View child, android.graphics.Rect rectangle, boolean immediate)

        // offset into coordinate space of this scroll view
        rectangle.offset(child.getLeft() - child.getScrollX(),
                child.getTop() - child.getScrollY());

        return scrollToChildRect(rectangle, immediate);
public voidrequestLayout()

        mIsLayoutDirty = true;
        super.requestLayout();
private booleanscrollAndFocus(int direction, int top, int bottom)

Scrolls the view to make the area defined by top and bottom visible. This method attempts to give the focus to a component visible in this area. If no component can be focused in the new visible area, the focus is reclaimed by this scrollview.

param
direction the scroll direction: {@link android.view.View#FOCUS_UP} to go upward {@link android.view.View#FOCUS_DOWN} to downward
param
top the top offset of the new area to be made visible
param
bottom the bottom offset of the new area to be made visible
return
true if the key event is consumed by this method, false otherwise

        boolean handled = true;

        int height = getHeight();
        int containerTop = getScrollY();
        int containerBottom = containerTop + height;
        boolean up = direction == View.FOCUS_UP;

        View newFocused = findFocusableViewInBounds(up, top, bottom);
        if (newFocused == null) {
            newFocused = this;
        }

        if (top >= containerTop && bottom <= containerBottom) {
            handled = false;
        } else {
            int delta = up ? (top - containerTop) : (bottom - containerBottom);
            doScrollY(delta);
        }

        if (newFocused != findFocus() && newFocused.requestFocus(direction)) {
            mScrollViewMovedFocus = true;
            mScrollViewMovedFocus = false;
        }

        return handled;
public voidscrollTo(int x, int y)
{@inheritDoc}

This version also clamps the scrolling to the bounds of our child.

        // we rely on the fact the View.scrollBy calls scrollTo.
        if (getChildCount() > 0) {
            View child = getChildAt(0);
            x = clamp(x, getWidth() - mPaddingRight - mPaddingLeft, child.getWidth());
            y = clamp(y, getHeight() - mPaddingBottom - mPaddingTop, child.getHeight());
            if (x != mScrollX || y != mScrollY) {
                super.scrollTo(x, y);
            }
        }
private voidscrollToChild(android.view.View child)
Scrolls the view to the given child.

param
child the View to scroll to

        child.getDrawingRect(mTempRect);

        /* Offset from child's local coordinates to ScrollView coordinates */
        offsetDescendantRectToMyCoords(child, mTempRect);

        int scrollDelta = computeScrollDeltaToGetChildRectOnScreen(mTempRect);

        if (scrollDelta != 0) {
            scrollBy(0, scrollDelta);
        }
private booleanscrollToChildRect(android.graphics.Rect rect, boolean immediate)
If rect is off screen, scroll just enough to get it (or at least the first screen size chunk of it) on screen.

param
rect The rectangle.
param
immediate True to scroll immediately without animation
return
true if scrolling was performed

        final int delta = computeScrollDeltaToGetChildRectOnScreen(rect);
        final boolean scroll = delta != 0;
        if (scroll) {
            if (immediate) {
                scrollBy(0, delta);
            } else {
                smoothScrollBy(0, delta);
            }
        }
        return scroll;
public voidsetFillViewport(boolean fillViewport)
Indicates this ScrollView whether it should stretch its content height to fill the viewport or not.

param
fillViewport True to stretch the content's height to the viewport's boundaries, false otherwise.

        if (fillViewport != mFillViewport) {
            mFillViewport = fillViewport;
            requestLayout();
        }
public voidsetSmoothScrollingEnabled(boolean smoothScrollingEnabled)
Set whether arrow scrolling will animate its transition.

param
smoothScrollingEnabled whether arrow scrolling will animate its transition

        mSmoothScrollingEnabled = smoothScrollingEnabled;
public final voidsmoothScrollBy(int dx, int dy)
Like {@link View#scrollBy}, but scroll smoothly instead of immediately.

param
dx the number of pixels to scroll by on the X axis
param
dy the number of pixels to scroll by on the Y axis

        long duration = AnimationUtils.currentAnimationTimeMillis() - mLastScroll;
        if (duration > ANIMATED_SCROLL_GAP) {
            if (localLOGV) Log.v(TAG, "Smooth scroll: mScrollY=" + mScrollY
                    + " dy=" + dy);
            mScroller.startScroll(mScrollX, mScrollY, dx, dy);
            invalidate();
        } else {
            if (!mScroller.isFinished()) {
                mScroller.abortAnimation();
            }
            if (localLOGV) Log.v(TAG, "Immediate scroll: mScrollY=" + mScrollY
                    + " dy=" + dy);
            scrollBy(dx, dy);
        }
        mLastScroll = AnimationUtils.currentAnimationTimeMillis();
public final voidsmoothScrollTo(int x, int y)
Like {@link #scrollTo}, but scroll smoothly instead of immediately.

param
x the position where to scroll on the X axis
param
y the position where to scroll on the Y axis

        smoothScrollBy(x - mScrollX, y - mScrollY);