How to capture the active control in Firemonkey?

Question

I am migrating a VCL application to FMX. I need to know the class of a control that has focus. The application works with various dynamically created frames with numerous input controls.
In VCL I use the VCL.Forms.TScreen.OnActiveControlChange as this is the one place to consistently capture the active control. This event is not available in FMX.Forms.TScreen. What would be an alternative approach in FMX?

iamjoosy · Accepted Answer · 2015-09-04 07:56:24Z

3

The most similar approach in FMX would be to listen to the TForm.OnFocusChanged event. From within the event handler you could then look up theTForm.Focused property.

answered Sep 4, 2015 at 7:56

iamjoosy

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2 Comments

Hans Over a year ago

This did the job. Thanks!

Tom Brunberg Over a year ago

@Hans To show your appreciation for the most helpful answer, you can click on the checkmark beside the answer (so it turns green). Read accepted-answer for more information about accepting answers.

Jon Souter · Accepted Answer · 2019-11-04 00:20:18Z

Sadly in Delphi 10.3, the approach outlined by @iamjoosy fails spectacularly with an 'Access Violation' under certain circumstances (especially when TabControls / TabItems are used as containers for other controls).

The code I am using:

procedure TForm1.FormFocusChanged(Sender: TObject); var Control : iControl; MyControl : TFMXObject; begin Control := form1.focused; try MyControl := TFmxObject(Control.GetObject); form1.Caption := MyControl.Name + ' of type ' + MyControl.ClassName; finally MyControl := nil; Control := nil; end; end;

Yet to add some intrigue, the above approach reverts to working fine if:

1) There's no TabControl/TabItem objects

2) If I add the following event handler to each child button (e.g. setting focus back to its parent TabItem):

procedure TForm1.Button2Click(Sender: TObject); begin TabItem1.SetFocus; end;

Hoping someone can offer advice as to whether I'm doing something stupid, or whether I've run into an FMX bug.

I'm using 10.3.3 with tabControls and as long as I don't enable my Form.FocusChanged event to access Form.Focused.GetObject.Name until everything has been rendered, it works fine. Then I put the dataset in Edit mode which moves focus to the first of many edit controls, and I accumulate a list of controls as I need, even as TAB moves focus to controls where I do not see indication of focus (which was my purpose). I have not determined how early in the FormCreate or FormShow one could enable this logging.

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