Title: TreeView control DragDrop Operation helper functions
Question: make Treeview control dragdrop operation programming easily.
1. expand/collaps automatically
2. move with children nodes
3. disable drop to child and self
4. auto scroll the control while the cursor near the top or bottom of the control
Answer:
unit TreeDragHelp;
interface
// TreeView control DragDrop Operation helper functions
// Author : bwsunv@163.com
// Date : 2003-05-04
// Features:
// 1. expand/collaps automatically
// 2. move with children nodes
// 3. disable drop to child and self
// 4. auto scroll the control while the cursor near the top
// or bottom of the control
// usage :
// In the 4 event functions call the bwXXXX
// event : StartDrag/EndDrag/DragOver/DragDrop
uses windows, classes, Controls, Forms, ComCtrls, ExtCtrls;
var
lastitem, dragitem : TTreeNode;
DragTimer : TTimer;
procedure bwTreeViewStartDrag(Sender: TObject;
var DragObject: TDragObject; timer1 : TTimer = nil);
procedure bwTreeViewEndDrag(Sender, Target: TObject; X, Y: Integer);
procedure bwTreeViewDragDrop(Sender, Source: TObject; X, Y: Integer);
procedure bwTreeViewDragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
// Timer used to expand / collasp automatically
procedure bwtimer(Sender : TObject);
implementation
procedure bwTreeViewStartDrag(Sender: TObject;
var DragObject: TDragObject; timer1 : TTimer);
begin
DragItem := (Sender as TTreeView).selected;
lastitem := nil;
DragTimer := Timer1;
if Assigned(DragTimer) then
begin
DragTimer.Enabled := False;
end;
end;
procedure bwTreeViewEndDrag(Sender, Target: TObject; X, Y: Integer);
begin
if Assigned(DragTimer) then
DragTimer.Enabled := false;
end;
procedure bwTreeViewDragDrop(Sender, Source: TObject; X, Y: Integer);
var
DropItem : TTreeNode;
begin
if Source = Sender then
begin
DropItem := (Sender as TTreeView).GetNodeAt (x, y);
dragitem.MoveTo(DropItem, naAddChild);
end;
end;
procedure bwTreeViewDragOver(Sender, Source: TObject; X, Y: Integer;
State: TDragState; var Accept: Boolean);
var
DropItem, TopItem : TTreeNode;
rt : TRect;
begin
Accept := False;
if Source = Sender then
begin
DropItem := (Sender as TTreeView).GetNodeAt (x, y);
if DropItem = nil then
begin
if Assigned(DragTimer) then
DragTimer.Enabled := False;
Exit;
end;
if DropItem lastitem then
begin
if Assigned(DragTimer) then
begin
DragTimer.Enabled := False;
DragTimer.Enabled := True;
end;
Lastitem := DropItem;
end;
// if on the top , auto scroll
if DropItem = (Sender as TTreeView).topitem then
begin
if (Sender as TTreeView).topitem.GetPrevVisible nil then
(Sender as TTreeView).topitem :=
(Sender as TTreeView).topitem.GetPrevVisible;
if DropItem (Sender as TTreeView).topitem then
Exit;
end;
rt := dropItem.DisplayRect (False);
//// if on the bottom, auto scroll
if rt.Bottom (Sender as TTreeView).Height - 8 then
begin
TopItem := (Sender as TTreeView).topitem;
if (Sender as TTreeView).topitem.GetNextVisible nil then
(Sender as TTreeView).topitem :=
(Sender as TTreeView).topitem.GetNextVisible;
if Topitem (Sender as TTreeView).topitem then
Exit;
end;
if DropItem = DragItem then// nothing
else
if DropItem.HasAsParent ( DragItem) = False then// not children
Accept := True;
if DragItem.HasAsparent(DropItem) = True then// don't collasp parent node
if Assigned(DragTimer) then
DragTimer.Enabled := False;
end;
end;
procedure bwtimer(Sender : TObject);
begin
if lastitem nil then
lastItem.Expanded := not LastItem.expanded;// expand/collaps automatically
end;
end.