Delphi自定义TTreeNode

Question

我试图制作我的自定义TTreeNode类

例如

TCustomTreeNode = class(TTreeNode)
  private
  public
    Comment:string;
  end;

我在树视图中创建并添加节点,如下所示:

var
  NewCustomTreeNode:TCustomTreeNode;
begin
  NewCustomTreeNode:= TCustomTreeNode.Create(TreeView.Items);
  NewCustomTreeNode.Comment:='blqblq';
  TreeView.Items.AddChild(NewCustomTreeNode,'NodeText');

当我尝试访问自定义创建的树节点时会弹出错误.例如,我喜欢这样:

TCustomTreeNode(TreeNode).Comment:='asdadssadas';

请帮助

Answer 1

代码的问题在于AddChild树视图中的结果调用会创建一个新节点.由于您没有告诉树视图创建子类的节点,因此它创建了一个普通的节点TTreeNode.然后当你试图将它投射到一个TCustomTreeNode世界时,世界就会结束.

您需要使用该OnCreateNodeClass方法来确保树视图能够创建新节点.像这样:

type
  TCustomTreeNode = class(TTreeNode)
  protected
    procedure Assign(Source: TPersistent); override;
  public
    Comment: string;
  end;

procedure TCustomTreeNode.Assign(Source: TPersistent);
begin
  if Source is TCustomTreeNode then
    Comment := TCustomTreeNode(Source).Comment;
  inherited;
end;


procedure TForm1.FormCreate(Sender: TObject);
var
  NewNode: TCustomTreeNode;
begin
  NewNode := TreeView1.Items.Add(nil, 'Node1') as TCustomTreeNode;
  NewNode.Comment := 'A comment';
  NewNode := TreeView1.Items.Add(nil, 'Node2') as TCustomTreeNode;
  NewNode.Comment := 'Another comment';
end;

procedure TForm1.TreeView1Click(Sender: TObject);
var
  Node: TCustomTreeNode;
begin
  Node := TreeView1.Selected as TCustomTreeNode;
  if Assigned(Node) then
    ShowMessage(Node.Comment);
end;

procedure TForm1.TreeView1CreateNodeClass(Sender: TCustomTreeView; var NodeClass: TTreeNodeClass);
begin
  NodeClass := TCustomTreeNode;
end;

我不能声称自己是世界上最伟大的Delphi树视图专家,但根据我的经验,你自己从不创建树节点.您应始终调用其中一个AddXXX方法TTreeView.Items来创建新节点.