DragSourceContext (Java Platform SE 8 )
Keywords: java.awt.dnd.DragSourceContext class
Date: 2020-03-26

java.awt.dnd

## Class DragSourceContext

- java.lang.Object
- - java.awt.dnd.DragSourceContext

- All Implemented Interfaces:
    DragSourceListener, DragSourceMotionListener, Serializable, EventListener

      public class DragSourceContext
      extends Object
      implements DragSourceListener, DragSourceMotionListener, Serializable

  The `DragSourceContext` class is responsible for managing the initiator side of the Drag and Drop protocol. In particular, it is responsible for managing drag event notifications to the DragSourceListeners and DragSourceMotionListeners, and providing the `Transferable` representing the source data for the drag operation.

  Note that the `DragSourceContext` itself implements the `DragSourceListener` and `DragSourceMotionListener` interfaces. This is to allow the platform peer (the `DragSourceContextPeer` instance) created by the `DragSource` to notify the `DragSourceContext` of state changes in the ongoing operation. This allows the `DragSourceContext` object to interpose itself between the platform and the listeners provided by the initiator of the drag operation.

  By default, `DragSourceContext` sets the cursor as appropriate for the current state of the drag and drop operation. For example, if the user has chosen the move action, and the pointer is over a target that accepts the move action, the default move cursor is shown. When the pointer is over an area that does not accept the transfer, the default "no drop" cursor is shown.

  This default handling mechanism is disabled when a custom cursor is set by the `setCursor(java.awt.Cursor)` method. When the default handling is disabled, it becomes the responsibility of the developer to keep the cursor up to date, by listening to the `DragSource` events and calling the `setCursor()` method. Alternatively, you can provide custom cursor behavior by providing custom implementations of the `DragSource` and the `DragSourceContext` classes.

  Since:
    1.2
  See Also:
    `DragSourceListener`, `DragSourceMotionListener`, `DnDConstants`, Serialized Form

- - ### Field Summary

    Fields
    Modifier and Type | Field and Description
    --- | ---
    `protected static int` | `CHANGED` An `int` used by updateCurrentCursor() indicating that the user operation has changed.
    `protected static int` | `DEFAULT` An `int` used by updateCurrentCursor() indicating that the `Cursor` should change to the default (no drop) `Cursor`.
    `protected static int` | `ENTER` An `int` used by updateCurrentCursor() indicating that the `Cursor` has entered a `DropTarget`.
    `protected static int` | `OVER` An `int` used by updateCurrentCursor() indicating that the `Cursor` is over a `DropTarget`.

  - ### Constructor Summary

    Constructors
    Constructor and Description
    `DragSourceContext(java.awt.dnd.peer.DragSourceContextPeer dscp, DragGestureEvent trigger, Cursor dragCursor, Image dragImage, Point offset, Transferable t, DragSourceListener dsl)` Called from `DragSource`, this constructor creates a new `DragSourceContext` given the `DragSourceContextPeer` for this Drag, the `DragGestureEvent` that triggered the Drag, the initial `Cursor` to use for the Drag, an (optional) `Image` to display while the Drag is taking place, the offset of the `Image` origin from the hotspot at the instant of the triggering event, the `Transferable` subject data, and the `DragSourceListener` to use during the Drag and Drop operation.

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `void` | `addDragSourceListener(DragSourceListener dsl)` Add a `DragSourceListener` to this `DragSourceContext` if one has not already been added.
    `void` | `dragDropEnd(DragSourceDropEvent dsde)` Calls `dragDropEnd` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDropEvent`.
    `void` | `dragEnter(DragSourceDragEvent dsde)` Calls `dragEnter` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDragEvent`.
    `void` | `dragExit(DragSourceEvent dse)` Calls `dragExit` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceEvent`.
    `void` | `dragMouseMoved(DragSourceDragEvent dsde)` Calls `dragMouseMoved` on the `DragSourceMotionListener`s registered with the `DragSource` associated with this `DragSourceContext`, and them passes the specified `DragSourceDragEvent`.
    `void` | `dragOver(DragSourceDragEvent dsde)` Calls `dragOver` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDragEvent`.
    `void` | `dropActionChanged(DragSourceDragEvent dsde)` Calls `dropActionChanged` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDragEvent`.
    `Component` | `getComponent()` Returns the `Component` associated with this `DragSourceContext`.
    `Cursor` | `getCursor()` Returns the current drag `Cursor`.
    `DragSource` | `getDragSource()` Returns the `DragSource` that instantiated this `DragSourceContext`.
    `int` | `getSourceActions()` Returns a bitwise mask of `DnDConstants` that represent the set of drop actions supported by the drag source for the drag operation associated with this `DragSourceContext`.
    `Transferable` | `getTransferable()` Returns the `Transferable` associated with this `DragSourceContext`.
    `DragGestureEvent` | `getTrigger()` Returns the `DragGestureEvent` that initially triggered the drag.
    `void` | `removeDragSourceListener(DragSourceListener dsl)` Removes the specified `DragSourceListener` from this `DragSourceContext`.
    `void` | `setCursor(Cursor c)` Sets the cursor for this drag operation to the specified `Cursor`.
    `void` | `transferablesFlavorsChanged()` Notifies the peer that the `Transferable`'s `DataFlavor`s have changed.
    `protected void` | `updateCurrentCursor(int sourceAct, int targetAct, int status)` If the default drag cursor behavior is active, this method sets the default drag cursor for the specified actions supported by the drag source, the drop target action, and status, otherwise this method does nothing.

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

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

- - ### Field Detail

    - #### DEFAULT

          protected static final int DEFAULT

      An `int` used by updateCurrentCursor() indicating that the `Cursor` should change to the default (no drop) `Cursor`.
      See Also:
        Constant Field Values

    - #### ENTER

          protected static final int ENTER

      An `int` used by updateCurrentCursor() indicating that the `Cursor` has entered a `DropTarget`.
      See Also:
        Constant Field Values

    - #### OVER

          protected static final int OVER

      An `int` used by updateCurrentCursor() indicating that the `Cursor` is over a `DropTarget`.
      See Also:
        Constant Field Values

    - #### CHANGED

          protected static final int CHANGED

      An `int` used by updateCurrentCursor() indicating that the user operation has changed.
      See Also:
        Constant Field Values

  - ### Constructor Detail

    - #### DragSourceContext

          public DragSourceContext(java.awt.dnd.peer.DragSourceContextPeer dscp,
                                   DragGestureEvent trigger,
                                   Cursor dragCursor,
                                   Image dragImage,
                                   Point offset,
                                   Transferable t,
                                   DragSourceListener dsl)

      Called from `DragSource`, this constructor creates a new `DragSourceContext` given the `DragSourceContextPeer` for this Drag, the `DragGestureEvent` that triggered the Drag, the initial `Cursor` to use for the Drag, an (optional) `Image` to display while the Drag is taking place, the offset of the `Image` origin from the hotspot at the instant of the triggering event, the `Transferable` subject data, and the `DragSourceListener` to use during the Drag and Drop operation.
      If `DragSourceContextPeer` is `null` `NullPointerException` is thrown.
      If `DragGestureEvent` is `null` `NullPointerException` is thrown.
      If `Cursor` is `null` no exception is thrown and the default drag cursor behavior is activated for this drag operation.
      If `Image` is `null` no exception is thrown.
      If `Image` is not `null` and the offset is `null` `NullPointerException` is thrown.
      If `Transferable` is `null` `NullPointerException` is thrown.
      If `DragSourceListener` is `null` no exception is thrown.
      Parameters:
        `dscp` - the `DragSourceContextPeer` for this drag
        `trigger` - the triggering event
        `dragCursor` - the initial `Cursor` for this drag operation or `null` for the default cursor handling; see class level documentation for more details on the cursor handling mechanism during drag and drop
        `dragImage` - the `Image` to drag (or `null`)
        `offset` - the offset of the image origin from the hotspot at the instant of the triggering event
        `t` - the `Transferable`
        `dsl` - the `DragSourceListener`
      Throws:
        `IllegalArgumentException` - if the `Component` associated with the trigger event is `null`.
        `IllegalArgumentException` - if the `DragSource` for the trigger event is `null`.
        `IllegalArgumentException` - if the drag action for the trigger event is `DnDConstants.ACTION_NONE`.
        `IllegalArgumentException` - if the source actions for the `DragGestureRecognizer` associated with the trigger event are equal to `DnDConstants.ACTION_NONE`.
        `NullPointerException` - if dscp, trigger, or t are null, or if dragImage is non-null and offset is null

  - ### Method Detail

    - #### getDragSource

          public DragSource getDragSource()

      Returns the `DragSource` that instantiated this `DragSourceContext`.
      Returns:
        the `DragSource` that instantiated this `DragSourceContext`

    - #### getComponent

          public Component getComponent()

      Returns the `Component` associated with this `DragSourceContext`.
      Returns:
        the `Component` that started the drag

    - #### getTrigger

          public DragGestureEvent getTrigger()

      Returns the `DragGestureEvent` that initially triggered the drag.
      Returns:
        the Event that triggered the drag

    - #### getSourceActions

          public int getSourceActions()

      Returns a bitwise mask of `DnDConstants` that represent the set of drop actions supported by the drag source for the drag operation associated with this `DragSourceContext`.
      Returns:
        the drop actions supported by the drag source

    - #### setCursor

          public void setCursor(Cursor c)

      Sets the cursor for this drag operation to the specified `Cursor`. If the specified `Cursor` is `null`, the default drag cursor behavior is activated for this drag operation, otherwise it is deactivated.
      Parameters:
        `c` - the initial `Cursor` for this drag operation, or `null` for the default cursor handling; see class level documentation for more details on the cursor handling during drag and drop

    - #### getCursor

          public Cursor getCursor()

      Returns the current drag `Cursor`.

      Returns:
        the current drag `Cursor`

    - #### addDragSourceListener

          public void addDragSourceListener(DragSourceListener dsl)
                                     throws TooManyListenersException

      Add a `DragSourceListener` to this `DragSourceContext` if one has not already been added. If a `DragSourceListener` already exists, this method throws a `TooManyListenersException`.

      Parameters:
        `dsl` - the `DragSourceListener` to add. Note that while `null` is not prohibited, it is not acceptable as a parameter.

      Throws:
        `TooManyListenersException` - if a `DragSourceListener` has already been added

    - #### removeDragSourceListener

          public void removeDragSourceListener(DragSourceListener dsl)

      Removes the specified `DragSourceListener` from this `DragSourceContext`.
      Parameters:
        `dsl` - the `DragSourceListener` to remove; note that while `null` is not prohibited, it is not acceptable as a parameter

    - #### transferablesFlavorsChanged

          public void transferablesFlavorsChanged()

      Notifies the peer that the `Transferable`'s `DataFlavor`s have changed.

    - #### dragEnter

          public void dragEnter(DragSourceDragEvent dsde)

      Calls `dragEnter` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDragEvent`.
      Specified by:
        `dragEnter` in interface `DragSourceListener`
      Parameters:
        `dsde` - the `DragSourceDragEvent`

    - #### dragOver

          public void dragOver(DragSourceDragEvent dsde)

      Calls `dragOver` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDragEvent`.
      Specified by:
        `dragOver` in interface `DragSourceListener`
      Parameters:
        `dsde` - the `DragSourceDragEvent`

    - #### dragExit

          public void dragExit(DragSourceEvent dse)

      Calls `dragExit` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceEvent`.
      Specified by:
        `dragExit` in interface `DragSourceListener`
      Parameters:
        `dse` - the `DragSourceEvent`

    - #### dropActionChanged

          public void dropActionChanged(DragSourceDragEvent dsde)

      Calls `dropActionChanged` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDragEvent`.
      Specified by:
        `dropActionChanged` in interface `DragSourceListener`
      Parameters:
        `dsde` - the `DragSourceDragEvent`

    - #### dragDropEnd

          public void dragDropEnd(DragSourceDropEvent dsde)

      Calls `dragDropEnd` on the `DragSourceListener`s registered with this `DragSourceContext` and with the associated `DragSource`, and passes them the specified `DragSourceDropEvent`.
      Specified by:
        `dragDropEnd` in interface `DragSourceListener`
      Parameters:
        `dsde` - the `DragSourceDropEvent`

    - #### dragMouseMoved

          public void dragMouseMoved(DragSourceDragEvent dsde)

      Calls `dragMouseMoved` on the `DragSourceMotionListener`s registered with the `DragSource` associated with this `DragSourceContext`, and them passes the specified `DragSourceDragEvent`.
      Specified by:
        `dragMouseMoved` in interface `DragSourceMotionListener`
      Parameters:
        `dsde` - the `DragSourceDragEvent`
      Since:
        1.4

    - #### getTransferable

          public Transferable getTransferable()

      Returns the `Transferable` associated with this `DragSourceContext`.
      Returns:
        the `Transferable`

    - #### updateCurrentCursor

          protected void updateCurrentCursor(int sourceAct,
                                             int targetAct,
                                             int status)

      If the default drag cursor behavior is active, this method sets the default drag cursor for the specified actions supported by the drag source, the drop target action, and status, otherwise this method does nothing.
      Parameters:
        `sourceAct` - the actions supported by the drag source
        `targetAct` - the drop target action
        `status` - one of the fields `DEFAULT`, `ENTER`, `OVER`, `CHANGED`

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