DragGestureRecognizer (Java Platform SE 8 )
Keywords: java.awt.dnd.DragGestureRecognizer class
Date: 2017-01-22

java.awt.dnd

## Class DragGestureRecognizer

- java.lang.Object
- - java.awt.dnd.DragGestureRecognizer

- All Implemented Interfaces:
    Serializable
  Direct Known Subclasses:
    MouseDragGestureRecognizer

      public abstract class DragGestureRecognizer
      extends Object
      implements Serializable

  The `DragGestureRecognizer` is an abstract base class for the specification of a platform-dependent listener that can be associated with a particular `Component` in order to identify platform-dependent drag initiating gestures.

  The appropriate `DragGestureRecognizer` subclass instance is obtained from the `DragSource` associated with a particular `Component`, or from the `Toolkit` object via its `createDragGestureRecognizer()` method.

  Once the `DragGestureRecognizer` is associated with a particular `Component` it will register the appropriate listener interfaces on that `Component` in order to track the input events delivered to the `Component`.

  Once the `DragGestureRecognizer` identifies a sequence of events on the `Component` as a drag initiating gesture, it will notify its unicast `DragGestureListener` by invoking its `gestureRecognized()` method.

  When a concrete `DragGestureRecognizer` instance detects a drag initiating gesture on the `Component` it is associated with, it fires a `DragGestureEvent` to the `DragGestureListener` registered on its unicast event source for `DragGestureListener` events. This `DragGestureListener` is responsible for causing the associated `DragSource` to start the Drag and Drop operation (if appropriate).

  See Also:
    `DragGestureListener`, `DragGestureEvent`, `DragSource`, Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected Component` | `component` The `Component` associated with this `DragGestureRecognizer`.
    `protected DragGestureListener` | `dragGestureListener` The `DragGestureListener` associated with this `DragGestureRecognizer`.
    `protected DragSource` | `dragSource` The `DragSource` associated with this `DragGestureRecognizer`.
    `protected ArrayList<InputEvent>` | `events` The list of events (in order) that the `DragGestureRecognizer` "recognized" as a "gesture" that triggers a drag.
    `protected int` | `sourceActions` An `int` representing the type(s) of action(s) used in this Drag and Drop operation.

  - ### Constructor Summary

    Constructors
    Modifier | Constructor and Description
    --- | ---
    `protected` | `DragGestureRecognizer(DragSource ds)` Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation.
    `protected` | `DragGestureRecognizer(DragSource ds, Component c)` Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation, and the `Component` this `DragGestureRecognizer` should "observe" for drag initiating gestures.
    `protected` | `DragGestureRecognizer(DragSource ds, Component c, int sa)` Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation, the `Component` this `DragGestureRecognizer` should "observe" for drag initiating gestures, and the action(s) supported for this Drag and Drop operation.
    `protected` | `DragGestureRecognizer(DragSource ds, Component c, int sa, DragGestureListener dgl)` Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation, the `Component` this `DragGestureRecognizer` should "observe" for drag initiating gestures, the action(s) supported for this Drag and Drop operation, and the `DragGestureListener` to notify once a drag initiating gesture has been detected.

  - ### Method Summary

    All Methods Instance Methods Abstract Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addDragGestureListener(DragGestureListener dgl)` Register a new `DragGestureListener`.
    `protected void` | `appendEvent(InputEvent awtie)` Listeners registered on the Component by this Recognizer shall record all Events that are recognized as part of the series of Events that go to comprise a Drag and Drop initiating gesture via this API.
    `protected void` | `fireDragGestureRecognized(int dragAction, Point p)` Notify the DragGestureListener that a Drag and Drop initiating gesture has occurred.
    `Component` | `getComponent()` This method returns the `Component` that is to be "observed" by the `DragGestureRecognizer` for drag initiating gestures.
    `DragSource` | `getDragSource()` This method returns the `DragSource` this `DragGestureRecognizer` will use in order to process the Drag and Drop operation.
    `int` | `getSourceActions()` This method returns an int representing the type of action(s) this Drag and Drop operation will support.
    `InputEvent` | `getTriggerEvent()` This method returns the first event in the series of events that initiated the Drag and Drop operation.
    `protected abstract void` | `registerListeners()` register this DragGestureRecognizer's Listeners with the Component subclasses must override this method
    `void` | `removeDragGestureListener(DragGestureListener dgl)` unregister the current DragGestureListener
    `void` | `resetRecognizer()` Reset the Recognizer, if its currently recognizing a gesture, ignore it.
    `void` | `setComponent(Component c)` set the Component that the DragGestureRecognizer is associated with registerListeners() and unregisterListeners() are called as a side effect as appropriate.
    `void` | `setSourceActions(int actions)` This method sets the permitted source drag action(s) for this Drag and Drop operation.
    `protected abstract void` | `unregisterListeners()` unregister this DragGestureRecognizer's Listeners with the Component subclasses must override this method

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Field Detail

    - #### dragSource

          protected DragSource dragSource

      The `DragSource` associated with this `DragGestureRecognizer`.

    - #### component

          protected Component component

      The `Component` associated with this `DragGestureRecognizer`.

    - #### dragGestureListener

          protected transient DragGestureListener dragGestureListener

      The `DragGestureListener` associated with this `DragGestureRecognizer`.

    - #### sourceActions

          protected int sourceActions

      An `int` representing the type(s) of action(s) used in this Drag and Drop operation.

    - #### events

          protected ArrayList<InputEvent> events

      The list of events (in order) that the `DragGestureRecognizer` "recognized" as a "gesture" that triggers a drag.

  - ### Constructor Detail

    - #### DragGestureRecognizer

          protected DragGestureRecognizer(DragSource ds,
                                          Component c,
                                          int sa,
                                          DragGestureListener dgl)

      Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation, the `Component` this `DragGestureRecognizer` should "observe" for drag initiating gestures, the action(s) supported for this Drag and Drop operation, and the `DragGestureListener` to notify once a drag initiating gesture has been detected.

      Parameters:
        `ds` - the `DragSource` this `DragGestureRecognizer` will use to process the Drag and Drop operation
        `c` - the `Component` this `DragGestureRecognizer` should "observe" the event stream to, in order to detect a drag initiating gesture. If this value is `null`, the `DragGestureRecognizer` is not associated with any `Component`.
        `sa` - the set (logical OR) of the `DnDConstants` that this Drag and Drop operation will support
        `dgl` - the `DragGestureRecognizer` to notify when a drag gesture is detected

      Throws:
        `IllegalArgumentException` - if ds is `null`.

    - #### DragGestureRecognizer

          protected DragGestureRecognizer(DragSource ds,
                                          Component c,
                                          int sa)

      Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation, the `Component` this `DragGestureRecognizer` should "observe" for drag initiating gestures, and the action(s) supported for this Drag and Drop operation.

      Parameters:
        `ds` - the `DragSource` this `DragGestureRecognizer` will use to process the Drag and Drop operation
        `c` - the `Component` this `DragGestureRecognizer` should "observe" the event stream to, in order to detect a drag initiating gesture. If this value is `null`, the `DragGestureRecognizer` is not associated with any `Component`.
        `sa` - the set (logical OR) of the `DnDConstants` that this Drag and Drop operation will support

      Throws:
        `IllegalArgumentException` - if ds is `null`.

    - #### DragGestureRecognizer

          protected DragGestureRecognizer(DragSource ds,
                                          Component c)

      Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation, and the `Component` this `DragGestureRecognizer` should "observe" for drag initiating gestures.

      Parameters:
        `ds` - the `DragSource` this `DragGestureRecognizer` will use to process the Drag and Drop operation
        `c` - the `Component` this `DragGestureRecognizer` should "observe" the event stream to, in order to detect a drag initiating gesture. If this value is `null`, the `DragGestureRecognizer` is not associated with any `Component`.

      Throws:
        `IllegalArgumentException` - if ds is `null`.

    - #### DragGestureRecognizer

          protected DragGestureRecognizer(DragSource ds)

      Construct a new `DragGestureRecognizer` given the `DragSource` to be used in this Drag and Drop operation.

      Parameters:
        `ds` - the `DragSource` this `DragGestureRecognizer` will use to process the Drag and Drop operation

      Throws:
        `IllegalArgumentException` - if ds is `null`.

  - ### Method Detail

    - #### registerListeners

          protected abstract void registerListeners()

      register this DragGestureRecognizer's Listeners with the Component subclasses must override this method

    - #### unregisterListeners

          protected abstract void unregisterListeners()

      unregister this DragGestureRecognizer's Listeners with the Component subclasses must override this method

    - #### getDragSource

          public DragSource getDragSource()

      This method returns the `DragSource` this `DragGestureRecognizer` will use in order to process the Drag and Drop operation.

      Returns:
        the DragSource

    - #### getComponent

          public Component getComponent()

      This method returns the `Component` that is to be "observed" by the `DragGestureRecognizer` for drag initiating gestures.

      Returns:
        The Component this DragGestureRecognizer is associated with

    - #### setComponent

          public void setComponent(Component c)

      set the Component that the DragGestureRecognizer is associated with registerListeners() and unregisterListeners() are called as a side effect as appropriate.

      Parameters:
        `c` - The `Component` or `null`

    - #### getSourceActions

          public int getSourceActions()

      This method returns an int representing the type of action(s) this Drag and Drop operation will support.

      Returns:
        the currently permitted source action(s)

    - #### setSourceActions

          public void setSourceActions(int actions)

      This method sets the permitted source drag action(s) for this Drag and Drop operation.

      Parameters:
        `actions` - the permitted source drag action(s)

    - #### getTriggerEvent

          public InputEvent getTriggerEvent()

      This method returns the first event in the series of events that initiated the Drag and Drop operation.

      Returns:
        the initial event that triggered the drag gesture

    - #### resetRecognizer

          public void resetRecognizer()

      Reset the Recognizer, if its currently recognizing a gesture, ignore it.

    - #### addDragGestureListener

          public void addDragGestureListener(DragGestureListener dgl)
                                      throws TooManyListenersException

      Register a new `DragGestureListener`.

      Parameters:
        `dgl` - the `DragGestureListener` to register with this `DragGestureRecognizer`.

      Throws:
        `TooManyListenersException` - if a `DragGestureListener` has already been added.

    - #### removeDragGestureListener

          public void removeDragGestureListener(DragGestureListener dgl)

      unregister the current DragGestureListener

      Parameters:
        `dgl` - the `DragGestureListener` to unregister from this `DragGestureRecognizer`

      Throws:
        `IllegalArgumentException` - if dgl is not (equal to) the currently registered `DragGestureListener`.

    - #### fireDragGestureRecognized

          protected void fireDragGestureRecognized(int dragAction,
                                                   Point p)

      Notify the DragGestureListener that a Drag and Drop initiating gesture has occurred. Then reset the state of the Recognizer.

      Parameters:
        `dragAction` - The action initially selected by the users gesture
        `p` - The point (in Component coords) where the gesture originated

    - #### appendEvent

          protected void appendEvent(InputEvent awtie)

      Listeners registered on the Component by this Recognizer shall record all Events that are recognized as part of the series of Events that go to comprise a Drag and Drop initiating gesture via this API.

      This method is used by a `DragGestureRecognizer` implementation to add an `InputEvent` subclass (that it believes is one in a series of events that comprise a Drag and Drop operation) to the array of events that this `DragGestureRecognizer` maintains internally.

      Parameters:
        `awtie` - the `InputEvent` to add to this `DragGestureRecognizer`'s internal array of events. Note that `null` is not a valid value, and will be ignored.

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