Delphi XE5 - Possibility of using Application(TApplication) variable in other units

Question

Using Delphi XE5 I'd like to use Application variable (TApplication type) in other unit's class. If I try to pass it with var or out parameter and then use it - I get Access Violation error. Is there a way to get data from Application in shared .pas library?

  for TempComponent in Application.MainForm do
      if (TempComponent is TTextControl) then
         ShowMessage('Text Assigned : ' + TempComponent.Name)
      else
         ShowMessage('No TTextControl Descendant : ' + TempComponent.Name);

I have included FMX.Forms in every unit. The above code works in main form class procedures, but when I use it in other unit I get AV in running application.

It is declared in the [`Forms`](http://docwiki.embarcadero.com/Libraries/en/Vcl.Forms.TApplication) unit. Just include `Forms` in your unit uses declaration. — LU RD, Feb 20 '14 at 10:47
@LURD, that doesn't explain *"if I try to pass it with var or out parameter and then use it..."*. OP must have the `Forms` unit included otherwise the `TApplication` type weren't recognized at compilation time. However, I don't get why accessing a passed instance of `Application` object would cause an AV. Xsawery, could you include a relevant code into your question ? — TLama, Feb 20 '14 at 10:55
Is this VCL or FMX. I believe this is FMX. You should tag the question accordingly so that you don't get VCL answers. — David Heffernan, Feb 20 '14 at 11:08

score 3 · Accepted Answer · answered Feb 20 '14 at 11:16

3

You state that this code:

for TempComponent in Application.MainForm do
  if (TempComponent is TTextControl) then
     ShowMessage('Text Assigned : ' + TempComponent.Name)
  else
     ShowMessage('No TTextControl Descendant : ' + TempComponent.Name);

results in an access violation. The only reasonable explanation for that is that either:

Application is nil, or
Application.MainForm is nil.

The former seems a little unlikely since you'd have to be running the code before the FMX.Forms unit intialized (or after it finalized). So the likely explanation is that you are running the code before the main form has been created, or you are running the code in a program that does not have a main form.

When you encounter access violation errors, you can debug them yourself to understand. What you need to do is to set a breakpoint on the line that causes the exception. When it triggers, inspect the variables used by that line of code. Usually you will find that one of the variables is nil.

answered Feb 20 '14 at 11:16

David Heffernan

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Looks like you right... when I call it OnCreate() of main TFrom there is AV... when OnButtonClick is OK... so how can I wait for the application to finish main TForm's creation? – Sebastian Xawery Wiśniowiecki Feb 20 '14 at 11:34
Well, I've no idea what you are really trying to do. But on `OnCreate` of the main form, you can refer to the main form using `Self`. – David Heffernan Feb 20 '14 at 11:39
I'm trying to swap all Text properties in TForm's children. – Sebastian Xawery Wiśniowiecki Feb 20 '14 at 12:02
OK. I think I answered the question that you asked. – David Heffernan Feb 20 '14 at 12:12
How can I use Self to get information if Self.Create() is finished? – Sebastian Xawery Wiśniowiecki Feb 20 '14 at 12:15
The `OnCreate` event handler is presumably a method of your main form class. And so has access to `Self`. Again, I answered the question that you asked as best as I can see possible. I cannot answer detailed questions on the specifics of code that I cannot see. – David Heffernan Feb 20 '14 at 12:39
I'd like to check in some place if TForm constructor Create finished the job and I can use TForm in my code... I have tried WHILE NOT Assigned(TForm) DO Sleep(100); ... but it didn't help. – Sebastian Xawery Wiśniowiecki Feb 20 '14 at 13:30

score 2 · Answer 2 · edited Feb 20 '14 at 11:15

2

Application is a global variable defined in FMX.Forms. So as long as you add FMX.Forms to your uses statement, you can use the Application.

edited Feb 20 '14 at 11:15

David Heffernan

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1,490

answered Feb 20 '14 at 10:47

Toon Krijthe

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I meant FMX.Forms Application variable – Sebastian Xawery Wiśniowiecki Feb 20 '14 at 11:09
It's added - no compiler errors, just AV in running application, when I comment Applcation callings there's no AV. – Sebastian Xawery Wiśniowiecki Feb 20 '14 at 11:27

Delphi XE5 - Possibility of using Application(TApplication) variable in other units

2 Answers2