multithreading - Determining that form is alive -


im have method of form loads data, data may take long time load. part of data optional , form can closed before data loaded:

procedure tform1.loaddata(sender: tobject); begin   // load , add data form   ...   tthread.createanonymousthread(procedure   begin     // long data loading     ...     tthread.synchronize(nil, procedure     begin       // add data form       ...     end);   end).start; end;

and question: best method determine form alive (not closed) fmx avoid exception when data thread should added? long loading mean not hours or ten's minutes, can 1 minute.

update: after closing form don't need additional data anymore , thread can terminated. terminated in way, neet without exception. have 

    tthread.synchronize(nil, procedure     begin       // add data form       try         ...       except       end;     end);

and works, search decision without exception

you can check visible property of form find form showing or closed, :

begin   form.show;   // load data   tthread.createanonymousthread(procedure   var    i, n : integer;   begin     // long data loading     n := 0;     := 0 1000000000      n := n + 1;      tthread.synchronize(nil, procedure     begin      if form.visible       form.label1.text := inttostr(n);        // add data form     end);   end).start; end;

but not idea, can't stop loading data when form closed. should create tthread class , use it's terminated flag cancel loading of data when form closed, example :

tmythread = class(tthread)   public    constructor create;   protected    procedure execute; override;  end;  ...  { tmythread }  constructor tmythread.create; begin  inherited create(true);  freeonterminate := true;  end;  procedure tmythread.execute; var  i, n : integer;  stop : boolean; begin  n := 0;  stop := false;   := 1 1000000000   begin    if terminated     begin      stop := true;      break;     end;     n := n + 1;   end;   if not stop   begin    synchronize(procedure                begin                 form.label1.text := inttostr(n);                end);   end; end;

show form , start thread :

var  mythread : tmythread; { global variable } ...  begin  form.show;   mythread := tmythread.create;  mythread.start; end;

and terminate thread when form closed :

procedure tform.formclose(sender: tobject; var action: tcloseaction); begin  if assigned(mythread)   begin    mythread.terminate;    mythread := nil;   end; end;

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