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Android Reference

DragEvent


android.view

Class DragEvent

  • All Implemented Interfaces:
    Parcelable


    public class DragEvent
    extends Object
    implements Parcelable
    Represents an event that is sent out by the system at various times during a drag and drop operation. It is a complex 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 X

    The getAction(), 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.

    • Field Detail

      • 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 drag. If the View wants to indicate that it is a valid drop target, it can also react by changing its appearance.

        A View only receives further drag events if it returns true in response to ACTION_DRAG_STARTED.

        See Also:
        ACTION_DRAG_ENDED, Constant Field Values
      • ACTION_DRAG_LOCATION

        public static final int ACTION_DRAG_LOCATION
        Action constant returned by getAction(): Sent to a View after ACTION_DRAG_ENTERED if the drag shadow is still within the View object's bounding box. The getX() and getY() methods supply the X and Y position of 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. If the user moves the drag shadow back into the View object's bounding box, the View receives an ACTION_DRAG_ENTERED again before receiving any more ACTION_DRAG_LOCATION events.

        See Also:
        ACTION_DRAG_ENTERED, getX(), getY(), Constant Field Values
      • 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. 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:
        getClipData(), getX(), getY(), Constant Field Values
      • 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 that received an ACTION_DRAG_STARTED event will receive the ACTION_DRAG_ENDED event even if they are not currently visible when the drag ends.

        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:
        ACTION_DRAG_STARTED, getResult(), Constant Field Values
      • 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. If the user moves the drag shadow back into the View object's bounding box, the View receives an ACTION_DRAG_ENTERED again before receiving any more ACTION_DRAG_LOCATION events.

        See Also:
        ACTION_DRAG_ENTERED, ACTION_DRAG_LOCATION, Constant Field Values
      • ACTION_DRAG_EXITED

        public static final int ACTION_DRAG_EXITED
        Action constant returned by getAction(): Signals that the user has moved the drag shadow outside the bounding box of the View. 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.

        See Also:
        Constant Field Values
    • Method Detail

      • getX

        public float getX()
        Gets the X coordinate of the drag point. The value is only valid if the event action is ACTION_DRAG_LOCATION or ACTION_DROP.
        Returns:
        The current drag point's Y coordinate
      • getClipData

        public ClipData getClipData()
        Returns the ClipData object sent to the system as part of the call to startDrag(). This method only returns valid data if the event action is ACTION_DROP.
        Returns:
        The ClipData sent to the system by startDrag().
      • getClipDescription

        public ClipDescription getClipDescription()
        Returns the ClipDescription object contained in the ClipData object sent to the system as part of the call to startDrag(). 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.

        Returns:
        The ClipDescription that was part of the ClipData sent to the system by startDrag().
      • getLocalState

        public Object getLocalState()
        Returns the local state object sent to the system as part of the call to startDrag(). 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.

        This method returns valid data for all event actions.

        Returns:
        The local state object sent to the system by startDrag().
      • 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:
        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.
      • recycle

        public final void recycle()
        Recycle the DragEvent, to be re-used by a later caller. After calling this function you must never touch the event again.
      • toString

        public String toString()
        Returns a string containing a concise, human-readable representation of this DragEvent object.
        Overrides:
        toString in class Object
        Returns:
        A string representation of the DragEvent object.
      • describeContents

        public int describeContents()
        Returns information about the Parcel representation of this DragEvent object.
        Specified by:
        describeContents in interface Parcelable
        Returns:
        Information about the Parcel representation.
      • writeToParcel

        public void writeToParcel(Parcel dest,
                         int flags)
        Creates a Parcel object from this DragEvent object.
        Specified by:
        writeToParcel in interface Parcelable
        Parameters:
        dest - A Parcel object in which to put the DragEvent object.
        flags - Flags to store in the Parcel.


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