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Overview

TeeTree provides built-in drag and drop functionality that allows users to reorganize nodes by dragging them to new positions within the same tree or between different trees.

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Basic Drag and Drop

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Enable Automatic Drag and Drop

The simplest way to enable drag and drop: 
procedure TForm1.FormCreate(Sender: TObject);
begin
  // Add some sample nodes
  Tree1.Add('abc').Add('123');
  Tree1.Add('Hello').Add('World');
  Tree1.Add('2002').Add('January').Add('14th');

  // Enable drag and drop of nodes
  Tree1.DragAndDrop.Automatic := True;
end;

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Toggle Drag and Drop

procedure TForm1.CheckBoxDragDropClick(Sender: TObject);
begin
  Tree1.DragAndDrop.Automatic := CheckBoxDragDrop.Checked;
end;

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Drag and Drop Between Trees

TeeTree supports dragging nodes between different tree controls: 
procedure TForm1.FormCreate(Sender: TObject);
begin
  // Enable drag and drop for both trees
  Tree1.DragAndDrop.Automatic := True;
  Tree2.DragAndDrop.Automatic := True;

  // Allow dragging TO other trees
  Tree1.DragAndDrop.ToOtherTree := True;
  Tree2.DragAndDrop.ToOtherTree := True;

  // Allow dragging FROM other trees
  Tree1.DragAndDrop.FromOtherTree := True;
  Tree2.DragAndDrop.FromOtherTree := True;
end;

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Drag and Drop Properties

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ToOtherTree

Allows dragging nodes from this tree to another tree: 
// Enable dragging nodes out of this tree
Tree1.DragAndDrop.ToOtherTree := True;

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FromOtherTree

Allows accepting nodes dragged from another tree: 
// Enable accepting nodes from other trees
Tree1.DragAndDrop.FromOtherTree := True;

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DragRoots

Allows dragging root nodes (nodes without parents): 
// Enable dragging root nodes
Tree1.DragAndDrop.DragRoots := True;

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DragToRoot

Allows dropping nodes at the root level: 
// Enable dropping nodes as root nodes
Tree1.DragAndDrop.DragToRoot := True;

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Complete Multi-Tree Example

Here’s a complete example with two trees and checkboxes to control drag and drop options: 
type
  TDragDropMultiForm = class(TForm)
    Tree1: TTree;
    Tree2: TTree;
    CheckBoxToOther: TCheckBox;
    CheckBoxFromOther: TCheckBox;
    CheckBoxDragRoots: TCheckBox;
    CheckBoxDragToRoot: TCheckBox;
    procedure FormCreate(Sender: TObject);
    procedure CheckBoxToOtherClick(Sender: TObject);
    procedure CheckBoxFromOtherClick(Sender: TObject);
    procedure CheckBoxDragRootsClick(Sender: TObject);
    procedure CheckBoxDragToRootClick(Sender: TObject);
  end;

procedure TDragDropMultiForm.FormCreate(Sender: TObject);
begin
  // Create sample hierarchy in Tree1
  with Tree1.Add('Project') do
  begin
    AddChild('Documentation');
    AddChild('Source Code').AddChild('Main.pas');
    AddChild('Tests');
  end;

  // Create sample hierarchy in Tree2
  with Tree2.Add('Archive') do
  begin
    AddChild('2023');
    AddChild('2024');
  end;

  // Enable basic drag and drop
  Tree1.DragAndDrop.Automatic := True;
  Tree2.DragAndDrop.Automatic := True;

  // Enable all drag and drop options
  Tree1.DragAndDrop.ToOtherTree := True;
  Tree1.DragAndDrop.FromOtherTree := True;
  Tree1.DragAndDrop.DragRoots := True;
  Tree1.DragAndDrop.DragToRoot := True;

  Tree2.DragAndDrop.ToOtherTree := True;
  Tree2.DragAndDrop.FromOtherTree := True;
  Tree2.DragAndDrop.DragRoots := True;
  Tree2.DragAndDrop.DragToRoot := True;
  
  // Set checkbox states
  CheckBoxToOther.Checked := True;
  CheckBoxFromOther.Checked := True;
  CheckBoxDragRoots.Checked := True;
  CheckBoxDragToRoot.Checked := True;
end;

procedure TDragDropMultiForm.CheckBoxToOtherClick(Sender: TObject);
begin
  Tree1.DragAndDrop.ToOtherTree := CheckBoxToOther.Checked;
  Tree2.DragAndDrop.ToOtherTree := CheckBoxToOther.Checked;
end;

procedure TDragDropMultiForm.CheckBoxFromOtherClick(Sender: TObject);
begin
  Tree1.DragAndDrop.FromOtherTree := CheckBoxFromOther.Checked;
  Tree2.DragAndDrop.FromOtherTree := CheckBoxFromOther.Checked;
end;

procedure TDragDropMultiForm.CheckBoxDragRootsClick(Sender: TObject);
begin
  Tree1.DragAndDrop.DragRoots := CheckBoxDragRoots.Checked;
  Tree2.DragAndDrop.DragRoots := CheckBoxDragRoots.Checked;
end;

procedure TDragDropMultiForm.CheckBoxDragToRootClick(Sender: TObject);
begin
  Tree1.DragAndDrop.DragToRoot := CheckBoxDragToRoot.Checked;
  Tree2.DragAndDrop.DragToRoot := CheckBoxDragToRoot.Checked;
end;

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User Experience

When drag and drop is enabled, users can:
  1. Click and hold on a node to start dragging
  2. Move the mouse to see a preview of where the node will be dropped
  3. Release the mouse to drop the node at the new location
  4. Drop on a node to make it a child of that node
  5. Drop between nodes to reorder siblings
  6. Drop on empty space to create a root node (if DragToRoot is enabled)

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Visual Feedback

TeeTree provides visual feedback during drag and drop:
  • The dragged node is highlighted
  • The target drop location is indicated
  • Invalid drop locations are shown differently
  • A preview of the node follows the cursor

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Restrictions

By default, drag and drop has these restrictions:
  • Root nodes cannot be dragged (unless DragRoots is enabled)
  • Nodes cannot be dropped as root nodes (unless DragToRoot is enabled)
  • Nodes cannot be dragged to other trees (unless ToOtherTree is enabled)
  • Nodes cannot be received from other trees (unless FromOtherTree is enabled)
  • A node cannot be dragged onto itself or its descendants

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Key Points

  • Set DragAndDrop.Automatic := True to enable basic drag and drop
  • Use ToOtherTree and FromOtherTree for multi-tree scenarios
  • Use DragRoots to allow dragging root nodes
  • Use DragToRoot to allow creating new root nodes via drag and drop
  • TeeTree automatically prevents invalid operations (like dropping a node onto itself)
  • Visual feedback guides users during drag and drop operations
  • All drag and drop properties can be changed at runtime

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