VirtualTreeView embedding button in the cells

delphi, virtualtreeview

Solution

I wrote a small program to create any control for a node. I found out that the best place to set the nodes control visibility it in `OnAfterPaint` event. The scrolling works as intended and there is almost zero flickering.

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, VirtualTrees, StdCtrls, Buttons, ExtCtrls;

type
  TForm1 = class(TForm)
    VirtualStringTree1: TVirtualStringTree;
    procedure FormCreate(Sender: TObject);            
    procedure VirtualStringTree1GetText(Sender: TBaseVirtualTree;
      Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
      var CellText: WideString);
    procedure VirtualStringTree1AfterPaint(Sender: TBaseVirtualTree;
      TargetCanvas: TCanvas);
    procedure VirtualStringTree1MeasureItem(Sender: TBaseVirtualTree;
      TargetCanvas: TCanvas; Node: PVirtualNode; var NodeHeight: Integer);  
  private
    procedure SetNodesControlVisibleProc(Sender: TBaseVirtualTree; Node: PVirtualNode; Data: Pointer; var Abort: Boolean);
    procedure SetNodeControlVisible(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex = NoColumn);
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

type
  TNodeData = record
    Text: WideString;
    Control: TControl;
  end;
  PNodeData = ^TNodeData;

{ Utility }
function IsNodeVisibleInClientRect(Tree: TBaseVirtualTree; Node: PVirtualNode;
  Column: TColumnIndex = NoColumn): Boolean;
var
  OutRect: TRect;
begin
  Result := Tree.IsVisible[Node] and
    Windows.IntersectRect(OutRect, Tree.GetDisplayRect(Node, Column, False), Tree.ClientRect);
end;

type
  TControlClass = class of TControl;

  TMyPanel = class(TPanel)
  public
    CheckBox: TCheckBox;
  end;

{ TForm1 }
procedure TForm1.FormCreate(Sender: TObject);

  function CreateNodeControl(Tree: TVirtualStringTree; Node: PVirtualNode; ControlClass: TControlClass): TControl;
  var
    NodeData: PNodeData;
  begin
    NodeData := Tree.GetNodeData(Node);
    NodeData.Control := ControlClass.Create(nil);
    with NodeData.Control do
    begin
      Parent := Tree; // Parent will destroy the control
      Height := Tree.DefaultNodeHeight;
      Visible := False;
    end;
    Tree.IsDisabled[Node] := True;
    Result := NodeData.Control;
  end;

  procedure InitializeNodeData(Node: PVirtualNode; const Text: WideString);
  var
    NodeData: PNodeData;
  begin
    NodeData := VirtualStringTree1.GetNodeData(Node);
    Initialize(NodeData^);
    NodeData.Text := Text;
  end;

var
  Node: PVirtualNode;
  MyPanel: TMyPanel;
  I: integer;
begin
  VirtualStringTree1.NodeDataSize := SizeOf(TNodeData);
  // trigger MeasureItem
  VirtualStringTree1.TreeOptions.MiscOptions := VirtualStringTree1.TreeOptions.MiscOptions + [toVariableNodeHeight]; 

  // Populate some nodes    
  for I := 1 to 5 do begin
    Node := VirtualStringTree1.AddChild(nil);
    InitializeNodeData(Node, Format('%d', [I]));
    Node := VirtualStringTree1.AddChild(Node);
    InitializeNodeData(Node, Format('%d.1', [I]));
  end;

  Node := VirtualStringTree1.AddChild(nil);
  InitializeNodeData(Node, '[TSpeedButton Parent]');
  Node := VirtualStringTree1.AddChild(Node);
  InitializeNodeData(Node, 'TSpeedButton');
  TSpeedButton(CreateNodeControl(VirtualStringTree1, Node, TSpeedButton)).Caption := '+';

  Node := VirtualStringTree1.AddChild(nil);
  InitializeNodeData(Node, '[TEdit Parent]');
  Node := VirtualStringTree1.AddChild(Node);
  InitializeNodeData(Node, 'TEdit');
  TEdit(CreateNodeControl(VirtualStringTree1, Node, TEdit)).Text := 'Hello';

  Node := VirtualStringTree1.AddChild(nil);
  InitializeNodeData(Node, '[TMyPanel Parent]');
  Node := VirtualStringTree1.AddChild(Node);
  InitializeNodeData(Node, 'TMyPanel');
  MyPanel := TMyPanel(CreateNodeControl(VirtualStringTree1, Node, TMyPanel));
  with MyPanel do
  begin
    Caption := 'TMyPanel';
    ParentBackground := False;
    CheckBox := TCheckBox.Create(nil);
    CheckBox.Caption := 'CheckBox';
    CheckBox.Left := 10;
    CheckBox.Top := 10;
    CheckBox.Parent := MyPanel;
  end;

  for I := 6 to 10 do begin
    Node := VirtualStringTree1.AddChild(nil);
    InitializeNodeData(Node, Format('%d', [I]));
    Node := VirtualStringTree1.AddChild(Node);
    InitializeNodeData(Node, Format('%d.1', [I]));
  end;
end;

procedure TForm1.VirtualStringTree1GetText(Sender: TBaseVirtualTree;
  Node: PVirtualNode; Column: TColumnIndex; TextType: TVSTTextType;
  var CellText: WideString);
var
  NodeData: PNodeData;
begin
  NodeData := Sender.GetNodeData(Node);
  if Assigned(NodeData) then
    CellText := NodeData.Text;
end;

procedure TForm1.SetNodeControlVisible(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex = NoColumn);
var
  NodeData: PNodeData;
  R: TRect;
begin
  NodeData := Tree.GetNodeData(Node);
  if Assigned(NodeData) and Assigned(NodeData.Control) then
  begin
    with NodeData.Control do
    begin
      Visible := IsNodeVisibleInClientRect(Tree, Node, Column)
                 and ((Node.Parent = Tree.RootNode) or (vsExpanded in Node.Parent.States));
      R := Tree.GetDisplayRect(Node, Column, False);
      BoundsRect := R;
    end;
  end;
end;

procedure TForm1.SetNodesControlVisibleProc(Sender: TBaseVirtualTree; Node: PVirtualNode; Data: Pointer; var Abort: Boolean);
begin
  SetNodeControlVisible(Sender, Node);
end;

procedure TForm1.VirtualStringTree1AfterPaint(Sender: TBaseVirtualTree;
  TargetCanvas: TCanvas);
begin
  // Iterate all Tree nodes and set visibility
  Sender.IterateSubtree(nil, SetNodesControlVisibleProc, nil);
end;

procedure TForm1.VirtualStringTree1MeasureItem(Sender: TBaseVirtualTree;
  TargetCanvas: TCanvas; Node: PVirtualNode; var NodeHeight: Integer);
var
  NodeData: PNodeData;
begin
  NodeData := Sender.GetNodeData(Node);
  if Assigned(NodeData) and Assigned(NodeData.Control) then
  // set node special height if control is TMyPanel
    if NodeData.Control is TMyPanel then
      NodeHeight := 50;
end;

end.

DFM:

object Form1: TForm1
  Left = 192
  Top = 124
  Width = 782
  Height = 365
  Caption = 'Form1'
  Color = clBtnFace
  Font.Charset = DEFAULT_CHARSET
  Font.Color = clWindowText
  Font.Height = -11
  Font.Style = []
  OldCreateOrder = False
  OnCreate = FormCreate
  DesignSize = (
    766
    327)
  PixelsPerInch = 96
  TextHeight = 13
  object VirtualStringTree1: TVirtualStringTree
    Left = 8
    Top = 8
    Width = 450
    Height = 277
    Anchors = [akLeft, akTop, akRight, akBottom]
    Header.AutoSizeIndex = 0
    Header.Font.Charset = DEFAULT_CHARSET
    Header.Font.Color = clWindowText
    Header.Font.Height = -11
    Header.Font.Name = 'MS Sans Serif'
    Header.Font.Style = []
    Header.MainColumn = -1
    TabOrder = 0
    OnAfterPaint = VirtualStringTree1AfterPaint
    OnGetText = VirtualStringTree1GetText
    OnMeasureItem = VirtualStringTree1MeasureItem
    Columns = <>
  end
end

Output:

Tested with Delphi 7, VT version 5.3.0, Windows 7

Problem

Original source