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Base class for managing drag operations and user feedback.
Source position: controls.pp line 513
type TDragObject = class |
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protected |
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procedure EndDrag(); virtual; |
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Called when a dragging operation ends. |
function GetDragImages; virtual; |
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Returns a list of images for dragging. |
function GetDragCursor(); virtual; |
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Returns the dragging cursor type (shape). |
public |
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constructor Create(); virtual; |
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Constructor for the class instance. |
constructor AutoCreate(); |
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Special constructor which enforces destruction of the object at the end of the dragging operation. |
procedure HideDragImage; virtual; |
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Asks the image list to hide the drag image. |
procedure ShowDragImage; virtual; |
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Asks the image list to show the drag image. |
property AlwaysShowDragImages: Boolean; [rw] |
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Should the image of dragged objects always be shown? |
property AutoCreated: Boolean; [r] |
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Was the drag object created automatically? |
property AutoFree: Boolean; [r] |
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Indicates whether the object shall be destroyed at the end of the dragging operation. |
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The control that is dragged (source). |
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Current mouse position in screen coordinates. |
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property DragTarget: TControl; [rw] |
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The control over which the object currently is dragged (target). |
property DragTargetPos: TPoint; [rw] |
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Mouse position in client coordinates of the DragTarget. |
property Dropped: Boolean; [r] |
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Indicates whether the drag object has been dropped yet. |
end; |
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Base class for managing drag operations and user feedback. |
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TObject |
Every dragging operation has an associated DragObject, holding references to the source and target controls, and other parameters for the customization of the visual user feedback.
A default DragObject is created automatically when a dragging operation starts, and is destroyed when the operation has ended; you do not need to maintain it. But an application can provide a customized DragObject in the TControl.OnStartDrag or TControl.OnStartDock handlers for the source control (the one being dragged).
| Remark: | AutoCreated DragObjects imply different behavior in the DragOver and DragDrop events, where the Source becomes the dragged control, while the DragObject itself is passed as Source. |
TDragObject is the ancestor of a whole tree of dragging objects, with the main branches supporting either drag-drop or drag-dock operations. The type of the operation is determined using the TControl.DragKind property in the source control.
| Remark: | In contrast to the Delphi implementation, Lazarus has moved a couple of methods into the drag performers; these methods are no longer available for customization. |
A Lazarus DragObject mainly supplies the cursor and images, used in visual user feedback. Drag-drop operations typically signal acceptance of an possible drop by variations of the mouse cursor, and optionally can attach to it shapes of the dragged object(s). Drag-dock operations instead show a docking rectangle, that snaps to possible target locations when the mouse moves over docksites.
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A drag object for dragging a control. |
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A drag object for drag-dock. |
| Version 3.2 | Generated 2024-02-25 | Home |