在Delphi XE7中在Android上第2次打开表单时访问冲突

Question

When I open my form for the first time I get no violation, but when I first select a TEdit field and then close the form and then recreate the form and open it I get the Violation.

Code for creating the form:

procedure TfrmNocoreDKS.actConfigExecute(Sender: TObject);
var
  confForm: TConfiguratie;
begin
  confForm := TConfiguratie.Create(nil);
  confForm.ShowModal(
    procedure(ModalResult: TModalResult)
    begin
      confForm.DisposeOf;//Also tried confForm.Free;
    end);
end;

I've also tried this for creating the form:

procedure TfrmNocoreDKS.actConfigExecute(Sender: TObject);
var
  confForm: TConfiguratie;
begin
  confForm := TConfiguratie.Create(nil);
  try
    confForm.ShowModal(
      procedure(ModalResult: TModalResult)
      begin
      end);
  finally
    confForm.free;
  end;
end;

Code for Closing the form:

procedure TConfiguratie.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := TCloseAction.caFree;
end;

Because the violation only appears when you click on any TEdit and then close the form I think it has something to do with the virtual keyboard, but i'm not sure. I don't have any methods that use the virtual keyboard itself.

Answer 1

Update

While my suggestions here are as documented, there are still problems with Android and multiple forms. See later in this post.

---

Do not call DisposeOf() or Free at all. The FormClose() and the caFree call is the key to make it work.

The documentation how to dispose of a modal dialog has been changed: Using FireMonkey Modal Dialog Boxes .

The FireMonkey architects has struggled with this for several versions now, and finally it works .

Example from doc how to create a modal dialog:

procedure MyCurrentForm.MyButtonClick(Sender: TObject);
var
  dlg: TMyModalForm;
begin
  // Create an instance of a form.
  dlg := TMyModalForm.Create(nil);

  // Configure the form. For example, give it a display name.
  dlg.Caption := 'My Modal Dialog Box';

  // Show your dialog box and provide an anonymous method that handles the closing of your dialog box.
  dlg.ShowModal(
    procedure(ModalResult: TModalResult)
    begin
      // Do something.
    end
  );
end;

And to free your modal dialog:

procedure TMyModalForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  Action := TCloseAction.caFree;
end;

---

Update

The OP has tried this solution and it does not work as expected.

Looking into QC, there are reports claiming that this does not work as expected on mobile android platforms:

RSP-9692 Runtime creation of forms in Android and

RSP-9665 Access Violation in FMX.Platform.Android SendCMGestureMessage .

(You must login to access them).

The latter explains what is happening. When the modal form is destroyed, it is possible that FFocusedControl points to a destroyed control. When ARC is trying to release FFocusedControl this will cause a segmentation fault. FFocusedControl must be declared [weak]. See the RSP-9665 for more details.

There is also QC-126524 [Android] Open/Close/Free sub form multiple times may cause crash on Android Platform when removing Focus from TEdit reporting the same thing and closed as resolved in XE7. This apparently not true.

Answer 2

Embarcadero documentation regarding FMX ShowModal and mobile platforms says

Caution: Modal dialog boxes are not supported in Android apps. Instead of calling ShowModal, you should call Show, and have the form return and call your event. We recommend that you not use modal dialogs on either of the mobile platforms (iOS and Android) because unexpected behavior can result. Not using modal dialogs eliminates potential problems in debugging and supporting your mobile apps.

Answer 3

This issue seemed to be only accuring in Delphi XE7. I am now using Delphi XE8 and don't have this problem anymore.