Why doesn't my run-time-created component appear on the form?

Question

I am testing the example that came from this Q&A Component Creation - Joining Components Together? to learn how to create a custom/composite component.

While the installed component from the example works dragging on to the form, I can't seem to create it at run time.

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;

I tried both self and Form1 as the owner. Played with properties of both the panel and the image.

Just not sure what I am doing wrong. No errors except when I forgot to add pngimage to my uses. Steps through the code just fine, nothing visually occurs for the run time creation.

Answer 1

You need to set Parent in the runtime code.

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;

The code in your question won't result in the control showing for a plain vanilla TPanel, or indeed any control.

From the documentation, with my emphasis:

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.