DragEvent
public
class
DragEvent
extends Object
implements
Parcelable
java.lang.Object | |
↳ | android.view.DragEvent |
Represents an event that is sent out by the system at various times during a drag and drop operation. It is a data structure that contains several important pieces of data about the operation and the underlying data.
View objects that receive a DragEvent call getAction()
, which returns
an action type that indicates the state of the drag and drop operation. This allows a View
object to react to a change in state by changing its appearance or performing other actions.
For example, a View can react to the ACTION_DRAG_ENTERED
action type by
by changing one or more colors in its displayed image.
During a drag and drop operation, the system displays an image that the user drags. This image is called a drag shadow. Several action types reflect the position of the drag shadow relative to the View receiving the event.
Most methods return valid data only for certain event actions. This is summarized in the
following table. Each possible getAction()
value is listed in the first column. The
other columns indicate which method or methods return valid data for that getAction() value:
getAction() Value | getClipDescription() | getLocalState() | getX() | getY() | getClipData() | getResult() |
---|---|---|---|---|---|---|
ACTION_DRAG_STARTED | X | X | X | X | ||
ACTION_DRAG_ENTERED | X | X | ||||
ACTION_DRAG_LOCATION | X | X | X | X | ||
ACTION_DRAG_EXITED | X | X | ||||
ACTION_DROP | X | X | X | X | X | |
ACTION_DRAG_ENDED | X | X |
The getAction()
,
getLocalState()
describeContents()
,
writeToParcel(Parcel, int)
, and
toString()
methods always return valid data.
Developer Guides
For a guide to implementing drag and drop features, read the Drag and Drop developer guide.
Summary
Constants | |
---|---|
int |
ACTION_DRAG_ENDED
Action constant returned by |
int |
ACTION_DRAG_ENTERED
Action constant returned by |
int |
ACTION_DRAG_EXITED
Action constant returned by |
int |
ACTION_DRAG_LOCATION
Action constant returned by |
int |
ACTION_DRAG_STARTED
Action constant returned by |
int |
ACTION_DROP
Action constant returned by |
Inherited constants |
---|
Fields | |
---|---|
public
static
final
Creator<DragEvent> |
CREATOR
A container for creating a DragEvent from a Parcel. |
Public methods | |
---|---|
int
|
describeContents()
Returns information about the |
int
|
getAction()
Inspect the action value of this event. |
ClipData
|
getClipData()
Returns the |
ClipDescription
|
getClipDescription()
Returns the |
Object
|
getLocalState()
Returns the local state object sent to the system as part of the call to
|
boolean
|
getResult()
Returns an indication of the result of the drag and drop operation. |
float
|
getX()
Gets the X coordinate of the drag point. |
float
|
getY()
Gets the Y coordinate of the drag point. |
String
|
toString()
Returns a string containing a concise, human-readable representation of this DragEvent object. |
void
|
writeToParcel(Parcel dest, int flags)
Creates a |
Inherited methods | |
---|---|
Constants
ACTION_DRAG_ENDED
public static final int ACTION_DRAG_ENDED
Action constant returned by getAction()
: Signals to a View that the drag and drop
operation has concluded. A View that changed its appearance during the operation should
return to its usual drawing state in response to this event.
All views with listeners that returned boolean true
for the ACTION_DRAG_STARTED
event will receive the ACTION_DRAG_ENDED event even if they are not currently visible when
the drag ends. Views removed during the drag operation won't receive the ACTION_DRAG_ENDED
event.
The View object can call getResult()
to see the result of the operation.
If a View returned true
in response to ACTION_DROP
, then
getResult() returns true
, otherwise it returns false
.
See also:
Constant Value: 4 (0x00000004)
ACTION_DRAG_ENTERED
public static final int ACTION_DRAG_ENTERED
Action constant returned by getAction()
: Signals to a View that the drag point has
entered the bounding box of the View.
If the View can accept a drop, it can react to ACTION_DRAG_ENTERED by changing its appearance in a way that tells the user that the View is the current drop target.
The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the drag shadow out of the View object's bounding box or into a descendant view that can accept the data. If the user moves the drag shadow back into the View object's bounding box or out of a descendant view that can accept the data, the View receives an ACTION_DRAG_ENTERED again before receiving any more ACTION_DRAG_LOCATION events.See also:
Constant Value: 5 (0x00000005)
ACTION_DRAG_EXITED
public static final int ACTION_DRAG_EXITED
Action constant returned by getAction()
: Signals that the user has moved the
drag shadow out of the bounding box of the View or into a descendant view that can accept
the data.
The View can react by changing its appearance in a way that tells the user that
View is no longer the immediate drop target.
After the system sends an ACTION_DRAG_EXITED event to the View, the View receives no more ACTION_DRAG_LOCATION events until the user drags the drag shadow back over the View.
Constant Value: 6 (0x00000006)
ACTION_DRAG_LOCATION
public static final int ACTION_DRAG_LOCATION
Action constant returned by getAction()
: Sent to a View after
ACTION_DRAG_ENTERED
while the drag shadow is still within the View object's bounding
box, but not within a descendant view that can accept the data. The getX()
and
getY()
methods supply
the X and Y position of the drag point within the View object's bounding box.
A View receives an ACTION_DRAG_ENTERED
event before receiving any
ACTION_DRAG_LOCATION events.
The system stops sending ACTION_DRAG_LOCATION events to a View once the user moves the drag shadow out of the View object's bounding box or into a descendant view that can accept the data. If the user moves the drag shadow back into the View object's bounding box or out of a descendant view that can accept the data, the View receives an ACTION_DRAG_ENTERED again before receiving any more ACTION_DRAG_LOCATION events.
See also:
Constant Value: 2 (0x00000002)
ACTION_DRAG_STARTED
public static final int ACTION_DRAG_STARTED
Action constant returned by getAction()
: Signals the start of a
drag and drop operation. The View should return true
from its
onDragEvent()
handler method or
OnDragListener.onDrag()
listener
if it can accept a drop. The onDragEvent() or onDrag() methods usually inspect the metadata
from getClipDescription()
to determine if they can accept the data contained in
this drag. For an operation that doesn't represent data transfer, these methods may
perform other actions to determine whether or not the View should accept the data.
If the View wants to indicate that it is a valid drop target, it can also react by
changing its appearance.
Views added or becoming visible for the first time during a drag operation receive this event when they are added or becoming visible.
A View only receives further drag events for the drag operation if it returns true
in response to ACTION_DRAG_STARTED.
See also:
Constant Value: 1 (0x00000001)
ACTION_DROP
public static final int ACTION_DROP
Action constant returned by getAction()
: Signals to a View that the user
has released the drag shadow, and the drag point is within the bounding box of the View and
not within a descendant view that can accept the data.
The View should retrieve the data from the DragEvent by calling getClipData()
.
The methods getX()
and getY()
return the X and Y position of the drop point
within the View object's bounding box.
The View should return true
from its View.onDragEvent(DragEvent)
handler or OnDragListener.onDrag()
listener if it accepted the drop, and false
if it ignored the drop.
The View can also react to this action by changing its appearance.
See also:
Constant Value: 3 (0x00000003)
Fields
CREATOR
public static final Creator<DragEvent> CREATOR
A container for creating a DragEvent from a Parcel.
Public methods
describeContents
public int describeContents ()
Returns information about the Parcel
representation of this DragEvent
object.
Returns | |
---|---|
int |
Information about the Parcel representation. |
getAction
public int getAction ()
Inspect the action value of this event.
Returns | |
---|---|
int |
One of the following action constants, in the order in which they usually occur during a drag and drop operation: |
getClipData
public ClipData getClipData ()
Returns the ClipData
object sent to the system as part of the call
to
startDragAndDrop()
.
This method only returns valid data if the event action is ACTION_DROP
.
Returns | |
---|---|
ClipData |
The ClipData sent to the system by startDragAndDrop(). |
getClipDescription
public ClipDescription getClipDescription ()
Returns the ClipDescription
object contained in the
ClipData
object sent to the system as part of the call to
startDragAndDrop()
.
The drag handler or listener for a View can use the metadata in this object to decide if the
View can accept the dragged View object's data.
This method returns valid data for all event actions except for ACTION_DRAG_ENDED
.
Returns | |
---|---|
ClipDescription |
The ClipDescription that was part of the ClipData sent to the system by startDragAndDrop(). |
getLocalState
public Object getLocalState ()
Returns the local state object sent to the system as part of the call to
startDragAndDrop()
.
The object is intended to provide local information about the drag and drop operation. For
example, it can indicate whether the drag and drop operation is a copy or a move.
The local state is available only to views in the activity which has started the drag operation. In all other activities this method will return null
This method returns valid data for all event actions.
Returns | |
---|---|
Object |
The local state object sent to the system by startDragAndDrop(). |
getResult
public boolean getResult ()
Returns an indication of the result of the drag and drop operation.
This method only returns valid data if the action type is ACTION_DRAG_ENDED
.
The return value depends on what happens after the user releases the drag shadow.
If the user releases the drag shadow on a View that can accept a drop, the system sends an
ACTION_DROP
event to the View object's drag event listener. If the listener
returns true
, then getResult() will return true
.
If the listener returns false
, then getResult() returns false
.
Notice that getResult() also returns false
if no ACTION_DROP
is sent. This
happens, for example, when the user releases the drag shadow over an area outside of the
application. In this case, the system sends out ACTION_DRAG_ENDED
for the current
operation, but never sends out ACTION_DROP
.
Returns | |
---|---|
boolean |
true if a drag event listener returned true in response to
ACTION_DROP . If the system did not send ACTION_DROP before
ACTION_DRAG_ENDED , or if the listener returned false in response to
ACTION_DROP , then false is returned. |
getX
public float getX ()
Gets the X coordinate of the drag point. The value is only valid if the event action is
ACTION_DRAG_STARTED
, ACTION_DRAG_LOCATION
or ACTION_DROP
.
Returns | |
---|---|
float |
The current drag point's X coordinate |
getY
public float getY ()
Gets the Y coordinate of the drag point. The value is only valid if the event action is
ACTION_DRAG_STARTED
, ACTION_DRAG_LOCATION
or ACTION_DROP
.
Returns | |
---|---|
float |
The current drag point's Y coordinate |
toString
public String toString ()
Returns a string containing a concise, human-readable representation of this DragEvent object.
Returns | |
---|---|
String |
A string representation of the DragEvent object. |
writeToParcel
public void writeToParcel (Parcel dest, int flags)
Creates a Parcel
object from this DragEvent object.
Parameters | |
---|---|
dest |
Parcel : A Parcel object in which to put the DragEvent object. |
flags |
int : Flags to store in the Parcel. |