delphi - 为什么我的运行时创建的组件没有出现在表单上？

Question

我正在测试来自此问答 Component Creation - Joining Components Together? 的示例了解如何创建自定义/复合组件。

虽然示例中安装的组件可以拖到表单上，但我似乎无法在运行时创建它。

procedure TForm1.Button1Click(Sender: TObject);
var
MyPanel2 : TMyPanel;
begin
MyPanel2 := TMyPanel.Create(Form1);
With MyPanel2 do
  begin
    Left := 10;
    Top := 10;
    Width := 400;
    Height := 400;
    Visible := True;
    Image.Picture.LoadFromFile('C:\test.png');
  end;
end;

我尝试了 self 和 Form1 作为所有者。使用面板和图像的属性。

只是不确定我做错了什么。没有错误，除非我忘记将 pngimage 添加到我的使用中。很好地单步执行代码，运行时创建在视觉上没有发生任何事情。

Answer 1

您需要设置Parent在运行时代码中。

MyPanel2 := TMyPanel.Create(Self);
with MyPanel2 do
begin
  Parent := Self;//oops, you forgot to set this
  SetBounds(10, 10, 400, 400);
  Image.Picture.LoadFromFile('C:\test.png');
end;

您问题中的代码不会导致控件显示为普通的 TPanel，或者实际上任何控件。

来自documentation ，我强调的是:

Specifies the parent of the control.

Use the Parent property to get or set the parent of the control. The parent of a control is the control that contains it. For example, if an application includes three radio buttons in a group box, the group box is the parent of the three radio buttons, and the radio buttons are the child controls of the group box.

To serve as a parent, a control must be an instance of a TWinControl descendant.

When creating a new control at run time, assign a Parent property value for the new control. Usually, this is a form, panel, group box, or a control that is designed to contain another. Changing the parent of a control moves the control onscreen so that it is displayed within the new parent. When the parent control moves, the child moves with the parent.