Android CarouselViewRenderer.OnElementChanged NullReferenceException

[shnaz]

Hey @alexrainman , thanks again for useful plugin.

I am experiencing the following exception when using CarouselView 2.3.0. (didnt help updating to 2.3.2)

PS. I tried to create a sample project, downloading this repo and using the Demo project. But Demo.Droid is broken. Wasn't able to build.

Xamarin caused by: android.runtime.JavaProxyThrowable: System.AggregateException: A Task's exception(s) were not observed either by Waiting on the Task or accessing its Exception property. As a result, the unobserved exception was rethrown by the finalizer thread. ---> System.NullReferenceException: Object reference not set to an instance of an object. at CarouselView.FormsPlugin.Android.CarouselViewRenderer.OnElementChanged (Xamarin.Forms.Platform.Android.ElementChangedEventArgs1[TElement] e) [0x00110] in <78f2e2234165408294ce634a82101454>:0 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (TElement element) [0x000f4] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:190 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:289 at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:74 at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:207 at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:58 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:334 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:193 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:289 at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:74 at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:207 at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:58 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:334 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:193 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:289 at Xamarin.Forms.Platform.Android.AppCompat.Platform+ModalContainer..ctor (Android.Content.Context context, Xamarin.Forms.Page modal) [0x00038] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:335 at Xamarin.Forms.Platform.Android.AppCompat.Platform.PresentModal (Xamarin.Forms.Page modal, System.Boolean animated) [0x0000d] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:285 at Xamarin.Forms.Platform.Android.AppCompat.Platform+<Xamarin-Forms-INavigation-PushModalAsync>d__30.MoveNext () [0x0004a] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:150 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156 at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128 at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:113 at Xamarin.Forms.Application+NavigationImpl+<OnPushModal>d__3.MoveNext () [0x0008d] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Application.cs:323 --- End of inner exception stack trace --- ---> (Inner Exception #0) System.NullReferenceException: Object reference not set to an instance of an object. at CarouselView.FormsPlugin.Android.CarouselViewRenderer.OnElementChanged (Xamarin.Forms.Platform.Android.ElementChangedEventArgs1[TElement] e) [0x00110] in <78f2e2234165408294ce634a82101454>:0 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (TElement element) [0x000f4] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:190 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:289 at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:74 at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:207 at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:58 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:334 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:193 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:289 at Xamarin.Forms.Platform.Android.VisualElementPackager.AddChild (Xamarin.Forms.VisualElement view, Xamarin.Forms.Platform.Android.IVisualElementRenderer oldRenderer, Xamarin.Forms.Platform.Android.RendererPool pool, System.Boolean sameChildren) [0x00023] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:74 at Xamarin.Forms.Platform.Android.VisualElementPackager.SetElement (Xamarin.Forms.VisualElement oldElement, Xamarin.Forms.VisualElement newElement) [0x00104] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:207 at Xamarin.Forms.Platform.Android.VisualElementPackager.Load () [0x00000] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementPackager.cs:58 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetPackager (Xamarin.Forms.Platform.Android.VisualElementPackager packager) [0x00007] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:334 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].SetElement (TElement element) [0x00111] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:193 at Xamarin.Forms.Platform.Android.VisualElementRenderer1[TElement].Xamarin.Forms.Platform.Android.IVisualElementRenderer.SetElement (Xamarin.Forms.VisualElement element) [0x00027] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\VisualElementRenderer.cs:126 at Xamarin.Forms.Platform.Android.Platform.CreateRenderer (Xamarin.Forms.VisualElement element) [0x0001f] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\Platform.cs:289 at Xamarin.Forms.Platform.Android.AppCompat.Platform+ModalContainer..ctor (Android.Content.Context context, Xamarin.Forms.Page modal) [0x00038] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:335 at Xamarin.Forms.Platform.Android.AppCompat.Platform.PresentModal (Xamarin.Forms.Page modal, System.Boolean animated) [0x0000d] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:285 at Xamarin.Forms.Platform.Android.AppCompat.Platform+d30.MoveNext () [0x0004a] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Platform.Android\AppCompat\Platform.cs:150 --- End of stack trace from previous location where exception was thrown --- at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw () [0x0000c] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/exceptionservices/exceptionservicescommon.cs:143 at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Threading.Tasks.Task task) [0x00047] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:187 at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Threading.Tasks.Task task) [0x0002e] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:156 at System.Runtime.CompilerServices.TaskAwaiter.ValidateEnd (System.Threading.Tasks.Task task) [0x0000b] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:128 at System.Runtime.CompilerServices.TaskAwaiter.GetResult () [0x00000] in /Users/builder/data/lanes/3819/96c7ba6c/source/mono/mcs/class/referencesource/mscorlib/system/runtime/compilerservices/TaskAwaiter.cs:113 at Xamarin.Forms.Application+NavigationImpl+d3.MoveNext () [0x0008d] in C:\BuildAgent2\work\aad494dc9bc9783\Xamarin.Forms.Core\Application.cs:323 <---

[shnaz]

@alexrainman have you had time to look into this?

[shnaz]

I get a null reference exception here... viewpager is null.

https://github.com/alexrainman/CarouselView/blob/master/CarouselView/CarouselView.FormsPlugin.Android/CarouselViewImplementation.cs/#L75

[alexrainman]

ViewPager shouldnt view null at that point. Cannot reproduce. Let me download and test repo.

[shnaz]

@alexrainman i figured it out. It was my solution setup that was causing this.

[alexrainman]

Awesome.

[alexrainman]

If my work is helping you, please help me back: https://xamarinhq.wufoo.com/forms/nominate-a-xamarin-mvp/

[alexrainman]

This is what i have done that is community visible:

• Alex has been pretty active sharing his knowledge and answering questions in StackOverflow, GitHub and Xamarin Forums.
• Alex has been open sourcing Xamarin components and plugin with the community, with more of 10 repositories being maintained on GitHub.
• One of Alex's Xamarin.Forms plugin, the CarouselView, is currently being pulled into the Xamarin.Forms core (xamarin/Xamarin.Forms#853). As an stable widget, this control has become the standard for Xamarin.Forms carousel screens with more that 16K downloads in NuGet and more than 100 solved and not open issues.
• Another Alex's plugin, the SegmentedControl (https://github.com/alexrainman/SegmentedControl), is a big candidate to be also pulled into Xamarin.Forms core.
• Plus Xamarin.Forms UI related plugins, Alex shares plugins to set app icon Badge, Google Analytics and KeyChain access.
• Alex shares his knowledge about cutting edge technologies like Couchbase NoSQL and MobileIron integration with Xamarin Apps.