c# - Coded UI Control.Exists. System.NullReferenceException -

i want check window exists after actions. try:

 protected override boolean ispresent()     {         if (_mainwindow == null)         {             _mainwindow = new winwindow();             _mainwindow.searchproperties[winwindow.propertynames.controlname] = "mainwindow";         }         return _mainwindow.exists;     } 

but if control not exist mainwindow.exists throws system.nullreferenceexception. can't understand why happens because mainwindow reference in code can't null. how can verify _mainwindow founded or not?

i've did wait window loading timeout. i've tried use mainwindow.findmainwindow().waitforcontrolexist(100000) doesn’t wait needed timeout. code not set needed timout:

playback.playbacksettings.searchtimeout = 100000; playback.playbacksettings.waitforreadytimeout = 100000; 

i use vs2013.

upd:

this code nre check:

protected override boolean ispresent() {     if (_mainwindow == null)     {         _mainwindow = new winwindow();         _mainwindow.searchproperties[winwindow.propertynames.controlname] = "mainwindow";     }     try     {         return _mainwindow.tryfind(); //todo wtf?     }     catch (nullreferenceexception e)     {         console.writeline("we've got nullreferenceexception");         console.writeline("_mainwindow reference " + ((_mainwindow == null) ? "null" : "not null"));         throw e;  //line 41     } } 

and result:

we've got nullreferenceexception _mainwindow reference not null attachments:  file:///project/testresults/user_win-fp7fmm7pub1%202017-04-09%2015_57_34/in/4acd6ac8-92ce-4746-8787-3aecfd63bdd8/win-fp7fmm7pub1/successlogintest.png  test method uitest.autotests.logintests.successlogintest threw exception:   system.nullreferenceexception: object reference not set instance of object.    in uitest.locators.mainwindow.ispresent() in mainwindow.cs: line 41    in uitest.locators.basewindow.wait() in basewindow.cs: line 34    in uitest.locators.mainwindow..ctor() in mainwindow.cs: line 18    in uitest.locators.loginwindow.clickenterbutton() in loginwindow.cs: line 57    in uitest.autotests.logintests.successlogintest() in logintests.cs: line 32 

exists not want use. can use tryfind() instead.

 protected override boolean ispresent()  {      if (_mainwindow == null)      {          _mainwindow = new winwindow();          _mainwindow.searchproperties[winwindow.propertynames.controlname] = "mainwindow";      }      return _mainwindow.tryfind();  } 

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