expand/collapse TreeView only by node image click

I have on my form a TreeView with a lots of items/nodes. When I double click a item of a node I run a procedure (depending of the clicked item).My problem is that I want it to expand/collapse only when I cl开发者_如何转开发ick on the icon of the node ( the + or - sign), not if I double click an item

similar question

You may use the AllowCollapse and AllowExpand parameters of the OnCollapsing and OnExpanding events, to prevent the node from being collapsed or expanded.

Combine that with the appropiate logic to recognize the part of the node being clicked on. If the generating click was on the icon, let the action progress, if not, then ignore it (setting AllowXxxxx:=false)

But be careful not to break keyboard navigation. So you will need to check the origin of the event, and in case of a keyboard event (cursor left/right) leave the action progress.

To keep track of the originator event, capture the OnMouseDown and OnKeyDown events, and set an internal indicator of the type of the latest one received, so you may check for the later OnCollapsing and OnExpanding event process.

I know, it's not a good solution but it works :).

procedure TForm1.TWDblClick(Sender: TObject);
begin
TW.Items.BeginUpdate;
TW.Selected.Expanded:=not TW.Selected.Expanded;
TW.Items.EndUpdate;
end;

unit TreeViewNav;

interface

uses
  SysUtils, Classes, Controls, ComCtrls, Messages;

type
  TNavTreeView = class(TTreeView)
  private
    procedure WMLButtonDblClk(var Message: TWMLButtonDblClk);
      message WM_LBUTTONDBLCLK;

  protected
    FNoCollapse: Boolean;
    function CanCollapse(Node: TTreeNode): Boolean; override;
  end;

implementation

{ TNavTreeView }

function TNavTreeView.CanCollapse(Node: TTreeNode): Boolean;
begin
  Result := not FNoCollapse and inherited;
  FNoCollapse := False;
end;

procedure TNavTreeView.WMLButtonDblClk(var Message: TWMLButtonDblClk);
var
  PX, PY: Integer;
  HT: THitTests;
begin
  with Message do
    if (Width > 32768) or (Height > 32768) then
      with CalcCursorPos do
      begin
        PX := X;
        PY := Y;
      end
    else
    begin
      PX := XPos;
      PY := YPos;
    end;

  HT := GetHitTestInfoAt(PX, PY);
  if htOnItem in HT then
  begin
    FNoCollapse := True;
  end;

  inherited;
end;

end.

If you are using VirtalTreeView

There is a setting that controls the double click expand in TreeOptions.MiscOptions

toToggleOnDblClick Toggle node expansion state when it is double clicked.