Nineth Chapter-delphi Drag-and-drop programming (3)

9.2.2 Receive drag items

Whether a control can receive a dragged item is determined by the control's OnDragOver event. In Tabset drag, the main point is to use the location of the mouse to judge.

Procedure Tform1.tabset1dragover (Sender, Source:tobject; X, Y:integer;

State:tdragstate; var accept:boolean);

Var

Droppos:integer;

Begin

If Source = TabSet1 Then

Begin

Droppos: = Tabset1.itematpos (Point (X, Y));

Accept: = (Droppos >-1) and (Droppos <> tabset1.tabindex) and

(Droppos < TabSet1.Tabs.Count);

End

Else

Accept: = False;

End

9.2.3 Drop Drag Item

When the OnDragOver event handler returns a accept of true and the project is dropped, the Ondragdrop event processing completes the drag drop response. In the Tabset drag-and-drop instance, the position of the label is changed.

Procedure Tform1.tabset1dragdrop (Sender, Source:tobject; X, Y:integer);

Var

Oldpos:integer;

Newpos:integer;

Begin

If Source = TabSet1 Then

Begin

Oldpos: = Tabset1.tabindex;

Newpos: = Tabset1.itematpos (Point (X, Y));

if (Newpos >-1) and (Newpos <> oldpos) Then

TabSet1.Tabs.Move (Oldpos, Newpos);

End

End

9.2.4 End Drag operation

There are two ways to end a drag operation: either the user releases the mouse button or the program uses the EndDrag method to forcibly abort the drag. There are two consequences of ending a drag operation: dropping is accepted or put down is ignored.

When the drag operation ends, the source control receives a message responding to the drag end event Onenddrag.