Now the memo editor has its own unit to live in the editor link should also live there. Moves relevant code from main and rename the object to TMemoEditorLink to be more clear.

source/memoeditor.pas

@@ -4,7 +4,7 @@ interface
 
 uses
   Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
-  Dialogs, StdCtrls, TntStdCtrls, Registry;
+  Dialogs, StdCtrls, TntStdCtrls, Registry, VirtualTrees;
 
 {$I const.inc}
 
@@ -21,6 +21,31 @@ type
   end;
 
 
+  // The editor link, instanciated by VirtualTree.CreateEditor
+  TMemoEditorLink = class(TInterfacedObject, IVTEditLink)
+  private
+    FForm: TfrmMemoEditor;
+    FTree: TCustomVirtualStringTree; // A back reference to the tree calling.
+    FNode: PVirtualNode;             // The node to be edited.
+    FColumn: TColumnIndex;           // The column of the node.
+    FTextBounds: TRect;              // Smallest rectangle around the text.
+    FStopping: Boolean;              // Set to True when the edit link requests stopping the edit action.
+  public
+    FieldType: Integer;
+    MaxInputLength: Integer;
+    constructor Create;
+    destructor Destroy; override;
+    function BeginEdit: Boolean; virtual; stdcall;
+    function CancelEdit: Boolean; virtual; stdcall;
+    function EndEdit: Boolean; virtual; stdcall;
+    function GetBounds: TRect; virtual; stdcall;
+    function PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; virtual; stdcall;
+    procedure ProcessMessage(var Message: TMessage); virtual; stdcall;
+    procedure SetBounds(R: TRect); virtual; stdcall;
+  end;
+
+
+
 implementation
 
 uses main, helpers;
@@ -58,4 +83,96 @@ begin
   memoText.SetFocus;
 end;
 
+
+constructor TMemoEditorLink.Create;
+begin
+  inherited;
+end;
+
+destructor TMemoEditorLink.Destroy;
+begin
+  inherited;
+  FForm.Free;
+end;
+
+
+function TMemoEditorLink.PrepareEdit(Tree: TBaseVirtualTree; Node: PVirtualNode; Column: TColumnIndex): Boolean; stdcall;
+// Retrieves the true text bounds from the owner tree.
+var
+  Text: WideString;
+  F: TFont;
+begin
+  Result := Tree is TCustomVirtualStringTree;
+  if not Result then
+    exit;
+
+  FTree := Tree as TVirtualStringTree;
+  FNode := Node;
+  FColumn := Column;
+
+  // Initial size, font and text of the node.
+  F := TFont.Create;
+  FTree.GetTextInfo(Node, Column, F, FTextBounds, Text);
+
+  // Create the editor form
+  FForm := TfrmMemoEditor.Create(Ftree);
+  FForm.Parent := Tree;
+  FForm.memoText.Font := F;
+  FForm.memoText.Text := Text;
+end;
+
+
+function TMemoEditorLink.BeginEdit: Boolean; stdcall;
+begin
+  Result := not FStopping;
+  if Result then
+    FForm.Show;
+end;
+
+
+function TMemoEditorLink.CancelEdit: Boolean; stdcall;
+begin
+  Result := not FStopping;
+  if Result then begin
+    FStopping := True;
+    FForm.Hide;
+    FTree.CancelEditNode;
+  end;
+end;
+
+
+function TMemoEditorLink.EndEdit: Boolean; stdcall;
+begin
+  Result := not FStopping;
+  if Result then try
+    FStopping := True;
+    if FForm.memoText.Text <> FTree.Text[FNode, FColumn] then
+      FTree.Text[FNode, FColumn] := FForm.memoText.Text;
+    FForm.Hide;
+  except
+    FStopping := False;
+    raise;
+  end;
+end;
+
+
+function TMemoEditorLink.GetBounds: TRect; stdcall;
+begin
+  Result := FForm.BoundsRect;
+end;
+
+
+procedure TMemoEditorLink.ProcessMessage(var Message: TMessage); stdcall;
+begin
+end;
+
+
+procedure TMemoEditorLink.SetBounds(R: TRect); stdcall;
+begin
+  // Sets the top left corner of the edit control
+  if not FStopping then
+    FForm.TopLeft := R.TopLeft;
+end;
+
+
 end.