| Representation of a clipped data on the clipboard.
ClippedData is a complex type containing one or Item instances,
each of which can hold one or more representations of an item of data.
For display to the user, it also has a label and iconic representation.
A ClipData contains a {@link ClipDescription}, which describes
important meta-data about the clip. In particular, its
{@link ClipDescription#getMimeType(int) getDescription().getMimeType(int)}
must return correct MIME type(s) describing the data in the clip. For help
in correctly constructing a clip with the correct MIME type, use
{@link #newPlainText(CharSequence, CharSequence)},
{@link #newUri(ContentResolver, CharSequence, Uri)}, and
{@link #newIntent(CharSequence, Intent)}.
Each Item instance can be one of three main classes of data: a simple
CharSequence of text, a single Intent object, or a Uri. See {@link Item}
for more details.
Developer Guides
For more information about using the clipboard framework, read the
Copy and Paste
developer guide.
Implementing Paste or Drop
To implement a paste or drop of a ClippedData object into an application,
the application must correctly interpret the data for its use. If the {@link Item}
it contains is simple text or an Intent, there is little to be done: text
can only be interpreted as text, and an Intent will typically be used for
creating shortcuts (such as placing icons on the home screen) or other
actions.
If all you want is the textual representation of the clipped data, you
can use the convenience method {@link Item#coerceToText Item.coerceToText}.
In this case there is generally no need to worry about the MIME types
reported by {@link ClipDescription#getMimeType(int) getDescription().getMimeType(int)},
since any clip item can always be converted to a string.
More complicated exchanges will be done through URIs, in particular
"content:" URIs. A content URI allows the recipient of a ClippedData item
to interact closely with the ContentProvider holding the data in order to
negotiate the transfer of that data. The clip must also be filled in with
the available MIME types; {@link #newUri(ContentResolver, CharSequence, Uri)}
will take care of correctly doing this.
For example, here is the paste function of a simple NotePad application.
When retrieving the data from the clipboard, it can do either two things:
if the clipboard contains a URI reference to an existing note, it copies
the entire structure of the note into a new note; otherwise, it simply
coerces the clip into text and uses that as the new note's contents.
{@sample development/samples/NotePad/src/com/example/android/notepad/NoteEditor.java
paste}
In many cases an application can paste various types of streams of data. For
example, an e-mail application may want to allow the user to paste an image
or other binary data as an attachment. This is accomplished through the
ContentResolver {@link ContentResolver#getStreamTypes(Uri, String)} and
{@link ContentResolver#openTypedAssetFileDescriptor(Uri, String, android.os.Bundle)}
methods. These allow a client to discover the type(s) of data that a particular
content URI can make available as a stream and retrieve the stream of data.
For example, the implementation of {@link Item#coerceToText Item.coerceToText}
itself uses this to try to retrieve a URI clip as a stream of text:
{@sample frameworks/base/core/java/android/content/ClipData.java coerceToText}
Implementing Copy or Drag
To be the source of a clip, the application must construct a ClippedData
object that any recipient can interpret best for their context. If the clip
is to contain a simple text, Intent, or URI, this is easy: an {@link Item}
containing the appropriate data type can be constructed and used.
More complicated data types require the implementation of support in
a ContentProvider for describing and generating the data for the recipient.
A common scenario is one where an application places on the clipboard the
content: URI of an object that the user has copied, with the data at that
URI consisting of a complicated structure that only other applications with
direct knowledge of the structure can use.
For applications that do not have intrinsic knowledge of the data structure,
the content provider holding it can make the data available as an arbitrary
number of types of data streams. This is done by implementing the
ContentProvider {@link ContentProvider#getStreamTypes(Uri, String)} and
{@link ContentProvider#openTypedAssetFile(Uri, String, android.os.Bundle)}
methods.
Going back to our simple NotePad application, this is the implementation
it may have to convert a single note URI (consisting of a title and the note
text) into a stream of plain text data.
{@sample development/samples/NotePad/src/com/example/android/notepad/NotePadProvider.java
stream}
The copy operation in our NotePad application is now just a simple matter
of making a clip containing the URI of the note being copied:
{@sample development/samples/NotePad/src/com/example/android/notepad/NotesList.java
copy}
Note if a paste operation needs this clip as text (for example to paste
into an editor), then {@link Item#coerceToText(Context)} will ask the content
provider for the clip URI as text and successfully paste the entire note. | 