How to handling uncaught exception easier in LAMW like in LCL?

[AFFRIZA 亜風実]

Currently, I've modified Laz_And_Controls jAsyncTask to become like bellow, because I'm too lazy to make try..except on every task. Not just that, I add "keepInBackground := False", because adding that into every task doesn't look makes sense to me.

Code: Pascal  [Select][+][-]

1.  procedure jAsyncTask.GenEvent_OnAsyncEventDoInBackground(Obj: TObject; progress: integer; out keepInBackground: boolean);
2. begin
3.   keepInBackground:= True;
4.   fExceptStr := '';
5.   try
6.     if Assigned(FOnDoInBackground) then
7.       FOnDoInBackground(Obj,progress,keepInBackground);
8.     keepInBackground := False;
9.   except
10.     on e: exception do
11.     begin
12.       keepInBackground := False;
13.       fExceptStr := e.Message;
14.     end;
15.   end;
16. end;
17.  
18. procedure jAsyncTask.GenEvent_OnAsyncEventPostExecute(Obj: TObject; progress: Integer);
19. begin
20.   if fExceptStr <> '' then
21.     gApp.ShowMessage('ASyncTask Exception Error', fExceptStr, 'OK');
22.   if Assigned(FOnPostExecute) then FOnPostExecute(Obj,progress);
23. end;
24.  

But still, the kinda unsatisfying result happens, it doesn't handle nil variable. It's okay for now because it handles most exceptions except the Access Violation.

I was trying to look to any LAMW sources because there's no loop in the jApp (everything handled by events) so jApp.OnException is impossible to use.

I've tried in this thread to modify the App.java template, but I have no idea because I don't speak Java. Maybe someone can tell me how to use this?

Does anyone have an idea?

Thank you. 

[Thaddy]

You can use this: https://www.freepascal.org/docs-html/rtl/system/errorproc.html
Be careful if you use sysutils, this needs to be declared *after* sysutils and you need to call the sysutils version for everything you do not handle yourself.(Need to save the sysutils version's address in that case.)

Note that on Android, you need the Java exception handling too, to Freepascal it is an external exception. That is easy to do, but not as easy as try/except.

[AFFRIZA 亜風実]

I do not really understand how to use that.

this needs to be declared *after* sysutils

What does that mean, is that can be used in library? Can I get the sample usage?

Like this one maybe?

Code: Pascal  [Select][+][-]

1. library controls;  //[by LAMW: Lazarus Android Module Wizard: 22/08/2019 13:12:35]
2.  
3. {$mode delphi}
4.  
5. uses
6.   {$IFDEF UNIX}
7.   cthreads,
8.   {$ENDIF}
9.   Classes, SysUtils, And_jni, And_jni_Bridge, AndroidWidget, Laz_And_Controls,
10.   Laz_And_Controls_Events, control_main;
11.  
12. {%region /fold 'LAMW generated code'}
13.  
14. procedure OnError(ErrNo: LongInt; Address: CodePointer; Frame: Pointer);
15. begin
16.   gApp.ShowMessage('An Error Occured!', 'Exception error at address: '+
17.     sysBackTraceStr(Address), 'OK');
18. end;
19.  
20. begin
21.   // I'm not quite sure about this
22.   ErrorProc := OnError;
23.   gApp := jApp.Create(nil);
24.   gApp.Title := 'LAMW JNI Android Bridges Library';
25.   gjAppName := 'id.estoh.tumbas.stockwriter';
26.   gjClassName := 'id/estoh/tumbas/stockwriter/Controls';
27.   gApp.AppName := gjAppName;
28.   gApp.ClassName := gjClassName;
29.   gApp.Initialize;
30.   gApp.CreateForm(TControlMain, ControlMain);
31. end.            
32.  

Btw, I'm just lost my mind maybe. So, I transformed all LAMW events like this 

Code: Pascal  [Select][+][-]

1. Procedure Java_Event_pOnClick(env: PJNIEnv; this: jobject; Obj: TObject; Value: integer);
2. begin
3.  
4.   //----update global "gApp": to whom it may concern------
5.   gApp.Jni.jEnv:= env;
6.   gApp.Jni.jThis:= this;
7.   //------------------------------------------------------
8.   // here we go
9.   try
10.     if not (Assigned(Obj)) then Exit;
11.     if Obj is jForm then
12.     begin
13.       jForm(Obj).UpdateJNI(gApp);
14.       jForm(Obj).GenEvent_OnClick(Obj);
15.       Exit;
16.     end;
17.     // and etc.
18.  
19.   except
20.     on e: exception do
21.     begin
22.       gApp.ShowMessage('Exception Error!', e.Message, 'OK');
23.     end;
24.   end;
25. end;
26.  

[commanderz]

Very useful information, helped me get rid of the errors that the "raise" method generated in the Indy library.
Thanks to author!

[jmpessoa]

So, I transformed all LAMW events like this..

Good!

I will try apply your solution to LAMW code!

Thank you!

SIDE NOTE:

Ref.
https://forum.lazarus.freepascal.org/index.php/topic,56590.0.html


By engkin

In general, exceptions inside Java code can be tested with ExceptionOccurred,
and should be cleared with ExceptionClear.


procedure TAndroidModule1.jButton1Click(Sender:TObject);
{$push}{$WriteableConst+}
const
  eIdx:integer=0;{$pop}
var
  e:array[0..2] of String=('3*(2+2)','2/0','2/4+');
  r:string;
begin
  jExpression1.SetFormula(e[eIdx],[]);
  r:=jExpression1.Evaluate.ToString;
  if gApp.Jni.jEnv^.ExceptionOccurred(gApp.Jni.jEnv)<>nil then
  begin
    gApp.Jni.jEnv^.ExceptionClear(gApp.Jni.jEnv);//<--- if you don't clear it, your app will be killed
    r:='ERROR';
  end;
 
  ShowMessage(e[eIdx]+' = '+r);
  inc(eIdx); if eIdx>High(e) then eIdx:=0;
end;