Closing a secondary delphi form causes the main fo

问题:

When showing a secondary form from the main form and from the second form showing a third form and then closing both forms will cause the main form to lose focus.

Using Delphi 2009 with XP SP3

Here are my steps for reproducing the problem:

1. Create a new VCL forms applications
2. Drag a button onto the created form
3. In the click handler create a new TForm1 and show it

Run the program. Click the button to show a second form. Click the button on the second form to create a third form. When closing both new forms the main form will lose its focus.

This is my code in the button click event handler:

// Using Self does not change the results
with TForm1.Create(nil) do
    show;

Is there any way to stop my main form from losing focus?

回答1:

After upgrading my Delphi installation from version 12.0.3170.16989 (no updates) to version 12.0.3420.21218 (update 3 & 4) I could not reproduce the problem anymore.

Seems like it was a bug that was fixed in the update.

回答2:

I don't see how what you describe creates a "child" Form.

But anyway, I just tried with exactly what you described in your steps and could not reproduce it in D2009 (updates 3 & 4), whether I create the 2nd "child" from the main Form or from the 1st "child", and whatever the order in which I close them.

So, there must be something else you did not tell...

回答3:

From a pure Win32 perspective Applications tend to loose focus when popup windows are closed because the underlying framework has an order of operations issue. Windows will not activate a disabled window, so, when destroying a modal popup window it is very important that the parent window is (reenabled) BEFORE DestroyWindow is called on the popup.

I have no idea how this might apply to development in delphi or vcl. The code sample does not imply you have a lot - or any - control over how modal popup windows are destroyed.

回答4:

Try the following (and avoid the with):

with TForm1.Create(nil) do begin
  show;
  activate;
  bringtofront;
end;

回答5:

Like François I cannot reproduce this behaviour with Delphi 2009 on Windows XP SP3. The form that was opened first gets the focus back as soon as the other forms are closed.

To be sure, is your project code:

program Project1;

uses
  Forms,
  Unit1 in 'Unit1.pas' {Form1};

{$R *.res}

begin
  Application.Initialize;
  Application.MainFormOnTaskbar := True;
  Application.CreateForm(TForm1, Form1);
  Application.Run;
end.

And your Unit code:

unit Unit1;

interface

uses
  Forms, Classes, Controls, StdCtrls;

type
  TForm1 = class(TForm)
    Button1: TButton;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}


procedure TForm1.Button1Click(Sender: TObject);
begin
  with TForm1.Create(nil) do
    Show;
end;

end.

Corrected the name of François, sorry