Mouse and Keyboard Events

Overview

TeeTree provides a rich event system for responding to mouse clicks, keyboard input, and other user interactions. Events are available at both the tree level and individual node/connection level.

Events are defined in TeeTree.pas starting at line 1848. Both VCL and FMX versions share the same event signatures.

Mouse Events

Tree-Level Click Events

OnClickShape
OnClickConnection
OnClickBackground

Fired when any node is clicked:

procedure TForm1.Tree1ClickShape(
  Sender: TTreeNodeShape; 
  Button: TMouseButton;
  Shift: TShiftState; 
  X, Y: Integer);
begin
  ShowMessage('Clicked: ' + Sender.Text.Text);
  
  // Check which button was clicked
  case Button of
    mbLeft:   Caption := 'Left click';
    mbRight:  Caption := 'Right click';
    mbMiddle: Caption := 'Middle click';
  end;
  
  // Check modifier keys
  if ssCtrl in Shift then
    Caption := Caption + ' + Ctrl';
  if ssShift in Shift then
    Caption := Caption + ' + Shift';
end;

From TeeTree.pas line 2217: property OnClickShape: TClickShapeEvent

Fired when a connection line is clicked:

procedure TForm1.Tree1ClickConnection(
  Sender: TTreeConnection;
  Button: TMouseButton;
  Shift: TShiftState;
  X, Y: Integer);
begin
  ShowMessage(
    Format('Connection: %s -> %s',
      [Sender.FromShape.Text.Text,
       Sender.ToShape.Text.Text])
  );
  
  // Select the connection
  Tree1.Connections.Selected := Sender;
end;

From TeeTree.pas line 2215-2216: property OnClickConnection: TClickConnectionEvent

Fired when clicking empty tree area:

procedure TForm1.Tree1ClickBackground(
  Sender: TCustomTree;
  Button: TMouseButton;
  Shift: TShiftState;
  X, Y: Integer);
begin
  // Clear selection when clicking background
  Tree1.Selected.Clear;
  
  // Or add new node at click position
  if Button = mbLeft then
    with Tree1.Add('New Node') do
    begin
      X0 := X;
      Y0 := Y;
    end;
end;

From TeeTree.pas line 2214: property OnClickBackground: TTreeClick

Node-Level Events

Individual nodes can have their own event handlers:

var
  Node: TTreeNodeShape;
begin
  Node := Tree1.Add('Click Me');
  
  // Assign node-specific click handler
  Node.OnClick := NodeClickHandler;
end;

procedure TForm1.NodeClickHandler(
  Sender: TTreeNodeShape;
  Button: TMouseButton;
  Shift: TShiftState;
  X, Y: Integer);
begin
  // This only fires for this specific node
  Sender.Brush.Color := clYellow;
end;

Node-level OnClick fires after tree-level OnClickShape. Both will execute if both are assigned.

Double-Click Events

Handle double-click interactions:

// Tree level - any node double-clicked
procedure TForm1.Tree1DblClickShape(
  Sender: TTreeNodeShape;
  Button: TMouseButton;
  Shift: TShiftState;
  X, Y: Integer);
begin
  // Edit node text on double-click
  Sender.Edit;
end;

// Connection double-click
procedure TForm1.Tree1DblClickConnection(
  Sender: TTreeConnection;
  Button: TMouseButton;
  Shift: TShiftState;
  X, Y: Integer);
begin
  // Show connection properties dialog
  EditConnection(Sender);
end;

From TreeEd.pas (lines 4205-4208), the editor sets up these events:

OnClickConnection     := TheTreeClickConnection;
OnClickShape          := nil;  // Editor handles differently
OnDblClickConnection  := TheTreeDblClickConnection;
OnDblClickShape       := TheTreeDblClickShape;

Mouse Move Events

procedure TForm1.Tree1MouseMove(
  Sender: TObject;
  Shift: TShiftState;
  X, Y: Integer);
var
  Node: TTreeNodeShape;
begin
  // Find shape under mouse
  Node := Tree1.ClickedShape(X, Y);
  
  if Assigned(Node) then
  begin
    // Show hint or highlight
    StatusBar1.SimpleText := Node.Text.Text;
    Node.Border.Color := clHighlight;
  end
  else
    StatusBar1.SimpleText := '';
end;

From TeeTree.pas (lines 7990-7995):

// Call the OnMouseMove event if assigned
procedure TTreeNodeShape.DoMouseMove(...);
begin
  if Assigned(FOnMouseMove) then
     FOnMouseMove(Self, Shift, X, Y);
end;

Keyboard Events

OnKeyDown Event

Handle keyboard input:

procedure TForm1.Tree1KeyDown(
  Sender: TObject;
  var Key: Word;
  Shift: TShiftState);
begin
  case Key of
    VK_DELETE:
      begin
        // Delete selected nodes
        if MessageDlg('Delete selected nodes?', 
                      mtConfirmation, [mbYes, mbNo], 0) = mrYes then
          Tree1.Selected.Delete;
        Key := 0;  // Mark as handled
      end;
    
    VK_ESCAPE:
      begin
        // Clear selection
        Tree1.Selected.Clear;
        Key := 0;
      end;
    
    VK_F2:
      begin
        // Edit selected node
        if Tree1.Selected.Count > 0 then
          Tree1.Selected.First.Edit;
        Key := 0;
      end;
    
    VK_UP, VK_DOWN, VK_LEFT, VK_RIGHT:
      begin
        // Navigation handled automatically
        // But you can customize behavior here
      end;
  end;
  
  // Check modifier keys
  if ssCtrl in Shift then
  begin
    case Key of
      Ord('C'): Tree1.Selected.Copy;    // Ctrl+C
      Ord('V'): Tree1.Selected.Paste;   // Ctrl+V
      Ord('X'): Tree1.Selected.Cut;     // Ctrl+X
      Ord('A'): SelectAllNodes;          // Ctrl+A
    end;
  end;
end;

From TeeTree.pas line 2244:

property OnKeyDown;  // Inherited from TControl

Text Editing Events

OnStartEditing

Fired when node text editing begins:

procedure TForm1.Tree1StartEditing(
  Sender: TTreeNodeShape);
begin
  // Save original text for potential cancel
  FOldText := Sender.Text.Text;
  
  // Or prevent editing certain nodes
  if Sender.Tag = 1 then
  begin
    ShowMessage('This node cannot be edited');
    Sender.StopEditing;
  end;
end;

OnStopEditing

Fired when editing completes:

procedure TForm1.Tree1StopEditing(
  Sender: TTreeNodeShape);
begin
  // Validate new text
  if Trim(Sender.Text.Text) = '' then
  begin
    ShowMessage('Text cannot be empty');
    Sender.Text.Text := 'Unnamed';
  end;
  
  // Update database, etc.
  SaveNodeToDatabase(Sender);
end;

From TreeEd.pas (line 4207), the editor uses this:

OnStopEditing := TheTreeStopEditing;

Selection Events

OnSelectShape and OnUnSelectShape

procedure TForm1.Tree1SelectShape(
  Sender: TTreeNodeShape);
begin
  // Node was selected
  Panel1.Caption := 'Selected: ' + Sender.Text.Text;
  
  // Load details panel
  LoadNodeDetails(Sender);
  
  // Highlight related nodes
  HighlightChildren(Sender);
end;

Expand/Collapse Events

OnExpandingCollapsing

Critical for virtual mode and dynamic trees:

procedure TForm1.Tree1ExpandingCollapsing(
  Sender: TTreeNodeShape;
  var Expand: Boolean);
begin
  if Expand then
  begin
    // Before expanding
    if Sender.Children.Count = 0 then
    begin
      // Load children on-demand (virtual mode)
      LoadChildrenFromDatabase(Sender);
    end;
    
    // Or prevent expansion
    if not UserHasPermission(Sender) then
    begin
      ShowMessage('Access denied');
      Expand := False;  // Cancel expansion
      Exit;
    end;
  end
  else
  begin
    // Before collapsing
    // You can prevent collapse by setting Expand := True
    if Sender.Tag = 1 then  // Keep important nodes expanded
      Expand := True;
  end;
end;

From TeeTree.pas (lines 12654-12657):

if Assigned(FOnExpandingCollapsing) then
   FOnExpandingCollapsing(AShape, Value);

AShape.FExpanded := Value;  // After calling event

The Expand parameter is var - you can modify it to cancel the expand/collapse action.

Advanced Events

OnMovingShape

Fired continuously while dragging:

procedure TForm1.Tree1MovingShape(
  Sender: TTreeNodeShape;
  var DeltaX, DeltaY: Integer);
begin
  // Snap to grid while dragging
  DeltaX := (DeltaX div 10) * 10;
  DeltaY := (DeltaY div 10) * 10;
  
  // Or constrain movement
  if Sender.X0 + DeltaX < 0 then
    DeltaX := -Sender.X0;  // Don't move past left edge
end;

OnResizingShape

Fired while resizing with handles:

procedure TForm1.Tree1ResizingShape(
  Sender: TTreeNodeShape;
  ACorner: TTreeShapeHandle;
  var DeltaX, DeltaY: Integer);
begin
  // Maintain aspect ratio
  if ssShift in GetKeyState then
  begin
    if Abs(DeltaX) > Abs(DeltaY) then
      DeltaY := DeltaX
    else
      DeltaX := DeltaY;
  end;
  
  // Enforce minimum size
  if (Sender.Width + DeltaX < 50) then
    DeltaX := 50 - Sender.Width;
end;

OnAfterDraw

Custom drawing after tree renders:

procedure TForm1.Tree1AfterDraw(Sender: TObject);
var
  R: TRect;
begin
  // Draw watermark
  with Tree1.Canvas do
  begin
    Font.Size := 48;
    Font.Color := clSilver;
    TextOut(10, 10, 'DRAFT');
  end;
  
  // Draw selection count
  if Tree1.Selected.Count > 1 then
  begin
    R := Tree1.ClientRect;
    Tree1.Canvas.TextOut(
      R.Right - 100, R.Top + 10,
      Format('%d selected', [Tree1.Selected.Count])
    );
  end;
end;

Event Properties Summary

From TeeTree.pas (lines 2214-2244):

property OnAfterDraw: TNotifyEvent;
property OnClickBackground: TTreeClick;
property OnClickConnection: TClickConnectionEvent;
property OnClickShape: TClickShapeEvent;
property OnDblClickConnection: TClickConnectionEvent;
property OnDblClickShape: TClickShapeEvent;
property OnDeletedShapes: TNotifyEvent;
property OnDeletingShapes: TDeletingShapesEvent;
property OnExpandingCollapsing: TExpandingCollapsingEvent;
property OnMovingShape: TMovingShapeEvent;
property OnNewConnection: TNewConnectionEvent;
property OnNewPolygon: TNewPolygonEvent;
property OnResizingShape: TResizingShapeEvent;
property OnSelectConnection: TSelectConnectionEvent;
property OnSelectShape: TSelectShapeEvent;
property OnStartEditing: TStartEditingEvent;
property OnStopEditing: TStopEditingEvent;
property OnUnSelectConnection: TUnSelectConnectionEvent;
property OnUnSelectShape: TUnSelectShapeEvent;
property OnZoom: TNotifyEvent;
property OnZoomedArea: TZoomedAreaEvent;

Best Practices

Check for nil

Always check if Sender is assigned before accessing properties.

Use var Parameters

Events with var parameters let you modify behavior (like canceling expand).

BeginUpdate/EndUpdate

Wrap bulk changes in BeginUpdate/EndUpdate for better performance.

Event Order Matters

Node events fire after tree events. Plan your logic accordingly.

The TeeTree editor (TreeEd.pas) is an excellent reference for event handling patterns. See lines 4190-4210 for how events are wired up.

Get Started

Core Concepts

Guides

VCL & FMX

Mouse and Keyboard Events

Overview

Mouse Events

Tree-Level Click Events

Node-Level Events

Double-Click Events

Mouse Move Events

Keyboard Events

OnKeyDown Event

Text Editing Events

Selection Events

OnSelectShape and OnUnSelectShape

Expand/Collapse Events

OnExpandingCollapsing

Advanced Events

OnMovingShape

OnResizingShape

OnAfterDraw

Event Properties Summary

Best Practices

Check for nil

Use var Parameters

BeginUpdate/EndUpdate

Event Order Matters

Build docs developers (and LLMs) love

Get Started

Core Concepts

Guides

VCL & FMX

​Overview

​Mouse Events

​Tree-Level Click Events

​Node-Level Events

​Double-Click Events

​Mouse Move Events

​Keyboard Events

​OnKeyDown Event

​Text Editing Events

​Selection Events

​OnSelectShape and OnUnSelectShape

​Expand/Collapse Events

​OnExpandingCollapsing

​Advanced Events

​OnMovingShape

​OnResizingShape

​OnAfterDraw

​Event Properties Summary

​Best Practices

Check for nil

Use var Parameters

BeginUpdate/EndUpdate

Event Order Matters

Build docs developers (and LLMs) love

Overview

Mouse Events

Tree-Level Click Events

Node-Level Events

Double-Click Events

Mouse Move Events

Keyboard Events

OnKeyDown Event

Text Editing Events

Selection Events

OnSelectShape and OnUnSelectShape

Expand/Collapse Events

OnExpandingCollapsing

Advanced Events

OnMovingShape

OnResizingShape

OnAfterDraw

Event Properties Summary

Best Practices