DragEventArgs.AllowedEffect Property

 

Gets which drag-and-drop operations are allowed by the originator (or source) of the drag event.

Namespace:   System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)

member AllowedEffect : DragDropEffects with get

Property Value

Type: System.Windows.Forms.DragDropEffects

One of the DragDropEffects values.

When a control initiates a drag-and-drop operation by calling the Control.DoDragDrop method, it specifies the permissible effects of the operation. For example, when you drag a file from a source, if the file is read-only (or from a read-only storage medium such as a CD), the source will indicate that the file can be copied, but not transferred, to the target.

Before attempting to perform an operation on the dragged data, you should examine this property to ensure that the operation is allowed.

The following example demonstrates a drag-and-drop operation between two ListBox controls. The example calls the DoDragDrop method when the drag action starts. The drag action starts if the mouse has moved more than SystemInformation.DragSize from the mouse location during the MouseDown event. The IndexFromPoint method is used to determine the index of the item to drag during the MouseDown event.

The example also demonstrates using custom cursors for the drag-and-drop operation. The example assumes that two cursor files, 3dwarro.cur and 3dwno.cur, exist in the application directory, for the custom drag and no-drop cursors, respectively. The custom cursors will be used if the UseCustomCursorsCheckCheckBox is checked. The custom cursors are set in the GiveFeedback event handler.

The keyboard state is evaluated in the DragOver event handler for the right ListBox, to determine what the drag operation will be based upon state of the SHIFT, CTRL, ALT, or CTRL+ALT keys. The location in the ListBox where the drop would occur is also determined during the DragOver event. If the data to drop is not a String, then the DragEventArgs.Effect is set to DragDropEffects.None. Finally, the status of the drop is displayed in the DropLocationLabelLabel.

The data to drop for the right ListBox is determined in the DragDrop event handler and the String value is added at the appropriate place in the ListBox. If the drag operation moves outside the bounds of the form, then the drag-and-drop operation is canceled in the QueryContinueDrag event handler.

This code excerpt demonstrates using the DragEventArgs class. See the DoDragDrop method for the complete code example.

No code example is currently available or this language may not be supported.

.NET Framework
Available since 1.1
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