Attempt to invoke virtual method 'void android.view.View.resolveLayoutParams()' on a null object reference - xamarin.android

Question

I have a ScrollView added to a FrameLayout. In a button click I remove the ScrollView from the FrameLayout and add an element derived from ViewGroup. If the button is clicked again the ViewGroup is removed and the ScrollView is added back. While adding the ScrollView back to the FrameLayout after removing the ViewGroup I get the following exception from the AddView method of the FrameLayout. Actually it is thrown from the AddView() method of ViewGroup class, since FrameLayout is derived from ViewGroup.
Unhandled Exception:
Java.Lang.NullPointerException: Attempt to invoke virtual method 'void
android.view.View.resolveLayoutParams()' on a null object reference
occurred
I have already tried to toggle the visibility of both Views instead of adding one and removing the other. But after toggling visibility, the application crashes every time when the FrameLayout's OnLayout is called such as when the Android keyboard appears or if the device orientation changes.
I am sorry that I am not able to provide the code. Because my code is very complex and I could not reproduce this problem in a simple sample. I just posted this question as a last resort.
I know it is not possible to get solution if code is not included. But any input related to this problem will be helpful.

Answer 1

Since you cannot provide the code here, I can only write part of the code to show your requirements:
in xaml,i add a ScrolView (with its children) and a LinearLayout(which as your ViewGroup) into a FrameLayout:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">
<FrameLayout
android:id="#+id/framelayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_above = "#+id/click"
>
<ScrollView
android:id="#+id/scroll"
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text ="text in scrollview"
/>
</LinearLayout>
</ScrollView>
<LinearLayout
android:id="#+id/linearlayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="gone"
>
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text ="text iFn LinearLayout"
/>
</LinearLayout>
</FrameLayout>
<Button
android:id = "#+id/click"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="click"
android:layout_alignParentBottom="true"
/>
</RelativeLayout>
in activity show and hide the Scrolview and LinearLayout by click Button:
private int num = 1;
protected override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
// Set our view from the "main" layout resource
SetContentView(Resource.Layout.activity_main);
Button button = FindViewById<Button>(Resource.Id.click);
FrameLayout frameLayout = FindViewById<FrameLayout>(Resource.Id.framelayout);
ScrollView scrollView = FindViewById<ScrollView>(Resource.Id.scroll);
LinearLayout linearLayout = FindViewById<LinearLayout>(Resource.Id.linearlayout);
button.Click += delegate
{
if (num % 2 ==0)
{
scrollView.Visibility = Android.Views.ViewStates.Gone;
linearLayout.Visibility = Android.Views.ViewStates.Visible;
}
else
{
linearLayout.Visibility = Android.Views.ViewStates.Gone;
scrollView.Visibility = Android.Views.ViewStates.Visible;
}
num++;
};
}