c# - Catch TargetInvocationException inside a Task.Factory.StartNew(() => -

i'm developing windows forms application c#, .net framework 4.0 , visual studio 2012 premium.

i have method:

private void firstphasebtn_click(object sender, eventargs e) {     var task = task.factory.startnew(() =>     {         if (_viewmodel == null)             _viewmodel = new mainviewmodel();          this.begininvoke((action)delegate()         {             labelloading.text = "creando orden...";             labelloading.visible = true;              models.firstphasemodel model = new models.firstphasemodel()             {                 // set data.             };              ordernumberlabel.text = _viewmodel.firstphase(model);              firstphasebtn.enabled = true;             labelloading.text = string.empty;             labelloading.visible = false;         });     });      try     {         task.wait();     }     catch (exception)     {         messagebox.show(this, _viewmodel.clientcustomerror, "error");     } } 

on _viewmodel.firstphase(model); http request web service.

my problem here try catch block doesn't work. unhandled exception.

i have tried run project in debug, release, , running executable file on release folder, unhandled exception.

i have tried put try catch block inside task, same result.

how can handled exception in task?

i have tried add this:

.continuewith(t =>             {                 labelloading.visible = false;                 labelloading.text = string.empty;                 messagebox.show(this, _viewmodel.clientcustomerror, "error");             },  taskcontinuationoptions.onlyonfaulted); 

but i'm still getting system.reflection.targetinvocationexception.

problem here:

this.begininvoke((action)delegate()     {         labelloading.text = "creando orden...";         labelloading.visible = true;          models.firstphasemodel model = new models.firstphasemodel()         {             // set data.         };          ordernumberlabel.text = _viewmodel.firstphase(model);          firstphasebtn.enabled = true;         labelloading.text = string.empty;         labelloading.visible = false;     }); 

once call begininvoke, you're running things on ui thread , out of task in turn, means tpl no longer able track , trace exceptions , combining them on aggregateexception.

this easier way demonstrate problem:

public partial class form1 : form {     public form1()     {         initializecomponent();     }      protected override void onshown(eventargs e)     {         base.onshown(e);         var task = task.factory.startnew(() =>         {             thread.sleep(1000);             begininvoke((action)delegate { throw new notimplementedexception(); });         });          try         {             task.wait();         }         catch (exception ex)         {             console.writeline(ex.message);         }     } } 

if run code, crash application (unless you've subscribed relevant catch exception handler can't remember anymore).

what need either move begininvoke code out (using task continuation on correct scheduler) or try/catching entirety of code inside begininvoke().

update:

this how rewrite code:

var task = task.factory.startnew(() =>         {             if (_viewmodel == null)             {                 _viewmodel = new mainviewmodel();             }         }).             continuewith(x =>             {                  labelloading.text = "creando orden...";                 labelloading.visible = true;                  models.firstphasemodel model = new models.firstphasemodel()                 {                     // set data.                 };                  ordernumberlabel.text = _viewmodel.firstphase(model);                  firstphasebtn.enabled = true;                 labelloading.text = string.empty;                 labelloading.visible = false;             }, taskscheduler.current).continuewith(result =>             {                 if (result.isfaulted)                 {                     // result , "consume" it.                     _log.error(result.exception);                 }             });