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delphiinheritancedelphi-7

Form object's event can't see inherited method

Problem summary: The OnClick event of a TForm object says that it can't find the method I specify; this method is defined in the Form's superclass, which I expected it to be inherited.

Here I define the base type (i.e. superclass) for the "RAM Editor" window, including a button and what its OnClick event should do.

// File: RAM_Editor_Common.pas
type
  TfrmBaseRamEditor = class(TForm)
    btnMapfileLaden: TToolButton;
    procedure MapfileLaden1Click(Sender: TObject);
    // ....

procedure TfrmBaseRamEditor.Mapfileladen1Click(Sender: TObject);
begin
  if not OpenDialog2.Execute then Exit;
  StatusBar1.Panels[2].Text := OpenDialog2.FileName;
end;

Here I define the sub-class:

// File: RAM_Editor_SXcp.pas
TfrmRAM_Editor_SXcp = class(RAM_Editor_Common.TfrmBaseRamEditor)

Here the sub-class's Form makes use of the button and sets the OnClick event to the method that was defined in the super-class:

// File: RAM_Editor_SXcp.dfm
object frmRAM_Editor_SXcp: TfrmRAM_Editor_SXcp
// ....
// ....
    object btnMapfileLaden: TToolButton
      Left = 75
      Top = 0
      Hint = 'Mapfile laden'
      Caption = 'btnMapfileLaden'
      OnClick = MapfileLaden1Click
      ImageIndex = 5
      ParentShowHint = False
      ShowHint = False
    end

But when I attempt to compile I get the error:

"The MapfileLaden1Click method referenced by btnMapfileLaden.OnClick does not exist. Remove this reference?"

Why can it not see the inherited method?

Solution

  • Your .dfm file is incorrect instead of:

    object frmRAM_Editor_SXcp: TfrmRAM_Editor_SXcp

    you need

    inherited frmRAM_Editor_SXcp: TfrmRAM_Editor_SXcp

    Similarly instead of:

    object btnMapfileLaden: TToolButton

    you need

    inherited btnMapfileLaden: TToolButton

    I guess you are trying to inject a common base class into an existing hierarchy. You've made the changes needed in the .pas file, but failed to make the corresponding changes needed in the .dfm file. The inherited keyword in the .dfm file is required by visual form inheritance.