Package org.eclipse.swt.dnd

# Interface DropTargetListener

All Superinterfaces:
  `EventListener`, `SWTEventListener`

All Known Subinterfaces:
  `ITextEditorDropTargetListener`, `TransferDropTargetListener`

All Known Implementing Classes:
  `CommonDropAdapter`, `DelegatingDropAdapter`, `DropTargetAdapter`, `DropTargetEffect`, `NavigatorDropAdapter`, `PluginDropAdapter`, `StyledTextDropTargetEffect`, `TableDropTargetEffect`, `TreeDropTargetEffect`, `ViewerDropAdapter`

public interface DropTargetListener extends SWTEventListener
The `DropTargetListener` class provides event notification to the application for DropTarget events.

As the user moves the cursor into, over and out of a Control that has been designated as a DropTarget, events indicate what operation can be performed and what data can be transferred if a drop where to occur at that point. The application can respond to these events and change the type of data that will be dropped by modifying event.currentDataType, or change the operation that will be performed by modifying the event.detail field or stop any drop from happening on the current target by setting the event.detail field to DND_DROP_NONE.

When the user causes a drop to happen by releasing the mouse over a valid drop target, the application has one last chance to change the data type of the drop through the DropAccept event. If the drop is still allowed, the DropAccept event is immediately followed by the Drop event. In the Drop event, the application can still change the operation that is performed but the data type is fixed.

See Also:
  - `DropTargetEvent`

## Method Summary

Modifier and Type
Method
Description
`void`
`dragEnter(DropTargetEvent event)`
The cursor has entered the drop target boundaries.
`void`
`dragLeave(DropTargetEvent event)`
The cursor has left the drop target boundaries OR the drop has been cancelled OR the data is about to be dropped.
`void`
`dragOperationChanged(DropTargetEvent event)`
The operation being performed has changed (usually due to the user changing the selected modifier key(s) while dragging).
`void`
`dragOver(DropTargetEvent event)`
The cursor is moving over the drop target.
`void`
`drop(DropTargetEvent event)`
The data is being dropped.
`void`
`dropAccept(DropTargetEvent event)`
The drop is about to be performed.

## Method Details

### dragEnter

void dragEnter(DropTargetEvent event)
The cursor has entered the drop target boundaries.

The following fields in the DropTargetEvent apply:

- (in)widget
- (in)time
- (in)x
- (in)y
- (in)dataTypes
- (in,out)currentDataType
- (in)operations
- (in,out)detail
- (in,out)feedback

The `operations` value is determined by the modifier keys pressed by the user. If no keys are pressed the `event.detail` field is set to DND.DROP_DEFAULT. If the application does not set the `event.detail` to something other than `DND.DROP_DEFAULT` the operation will be set to the platform defined standard default.

The `currentDataType` is determined by the first transfer agent specified in setTransfer() that matches a data type provided by the drag source.

It is possible to get a DragEnter event when the drag source does not provide any matching data. In this case, the default operation is DND.DROP_NONE and the currentDataType is null.

The application can change the operation that will be performed by modifying the `detail` field but the choice must be one of the values in the `operations` field or DND.DROP_NONE.

The application can also change the type of data being requested by modifying the `currentDataTypes` field but the value must be one of the values in the `dataTypes` list.

Parameters:
  `event` - the information associated with the drag enter event
See Also:
  - `DropTargetEvent`

### dragLeave

void dragLeave(DropTargetEvent event)
The cursor has left the drop target boundaries OR the drop has been cancelled OR the data is about to be dropped.

The following fields in the DropTargetEvent apply:

- (in)widget
- (in)time
- (in)x
- (in)y
- (in)dataTypes
- (in)currentDataType
- (in)operations
- (in)detail

Parameters:
  `event` - the information associated with the drag leave event
See Also:
  - `DropTargetEvent`

### dragOperationChanged

void dragOperationChanged(DropTargetEvent event)
The operation being performed has changed (usually due to the user changing the selected modifier key(s) while dragging).

The following fields in the DropTargetEvent apply:

- (in)widget
- (in)time
- (in)x
- (in)y
- (in)dataTypes
- (in,out)currentDataType
- (in)operations
- (in,out)detail
- (in,out)feedback

The `operations` value is determined by the modifier keys pressed by the user. If no keys are pressed the `event.detail` field is set to DND.DROP_DEFAULT. If the application does not set the `event.detail` to something other than `DND.DROP_DEFAULT` the operation will be set to the platform defined standard default.

The `currentDataType` value is determined by the value assigned to `currentDataType` in previous dragEnter and dragOver calls.

The application can change the operation that will be performed by modifying the `detail` field but the choice must be one of the values in the `operations` field.

The application can also change the type of data being requested by modifying the `currentDataTypes` field but the value must be one of the values in the `dataTypes` list.

Parameters:
  `event` - the information associated with the drag operation changed event
See Also:
  - `DropTargetEvent`

### dragOver

void dragOver(DropTargetEvent event)
The cursor is moving over the drop target.

The following fields in the DropTargetEvent apply:

- (in)widget
- (in)time
- (in)x
- (in)y
- (in)dataTypes
- (in,out)currentDataType
- (in)operations
- (in,out)detail
- (in,out)feedback

The `operations` value is determined by the value assigned to `currentDataType` in previous dragEnter and dragOver calls.

The `currentDataType` value is determined by the value assigned to `currentDataType` in previous dragEnter and dragOver calls.

The application can change the operation that will be performed by modifying the `detail` field but the choice must be one of the values in the `operations` field.

The application can also change the type of data being requested by modifying the `currentDataTypes` field but the value must be one of the values in the `dataTypes` list.

NOTE: At this point the `data` field is null. On some platforms, it is possible to obtain the data being transferred before the transfer occurs but in most platforms this is not possible. On those platforms where the data is available, the application can access the data as follows:

     public void dragOver(DropTargetEvent event) {
           TextTransfer textTransfer = TextTransfer.getInstance();
           String data = (String)textTransfer.nativeToJava(event.currentDataType);
           if (data != null) {
               System.out.println("Data to be dropped is (Text)"+data);
           }
     };

Parameters:
  `event` - the information associated with the drag over event
See Also:
  - `DropTargetEvent`

### drop

void drop(DropTargetEvent event)
The data is being dropped. The data field contains java format of the data being dropped. To determine the type of the data object, refer to the documentation for the Transfer subclass specified in event.currentDataType.

The following fields in DropTargetEvent apply:

- (in)widget
- (in)time
- (in)x
- (in)y
- (in,out)detail
- (in)currentDataType
- (in)data

The application can refuse to perform the drop operation by setting the detail field to DND.DROP_NONE.

Parameters:
  `event` - the information associated with the drop event
See Also:
  - `DropTargetEvent`

### dropAccept

void dropAccept(DropTargetEvent event)
The drop is about to be performed. The drop target is given a last chance to change the nature of the drop.

The following fields in the DropTargetEvent apply:

- (in)widget
- (in)time
- (in)x
- (in)y
- (in)dataTypes
- (in,out)currentDataType
- (in)operations
- (in,out)detail

The application can veto the drop by setting the `event.detail` field to `DND.DROP_NONE`.

The application can change the operation that will be performed by modifying the `detail` field but the choice must be one of the values in the `operations` field.

The application can also change the type of data being requested by modifying the `currentDataTypes` field but the value must be one of the values in the `dataTypes` list.

Parameters:
  `event` - the information associated with the drop accept event
See Also:
  - `DropTargetEvent`