crc643f46942d9dd1fff9.FormsAppCompatActivity.n_onStart java.lang.IllegalStateException

need help.

I don't know why my app isn't working or force close.
I use Xamarin.Forms 5.0.0.2012

with the following error: crc643f46942d9dd1fff9.FormsAppCompatActivity.n_onStart java.lang.IllegalStateException

Stack trace: Type java.lang.IllegalStateException Exception java.lang.IllegalStateException: at androidx.fragment.app.Fragment$5.onFindViewById (Fragment.java:3042) at androidx.frag ment.app.FragmentStateManager.createView (FragmentStateManager.java:504) at androidx.fragment.app.FragmentStateManager.moveToExpectedState (FragmentStateManager.java:261) at androidx.fragment.app.FragmentStore.moveToExpectedState (FragmentStore.java:113) at androidx.fragment.app.FragmentManager.moveToState (FragmentManager.java:1433) at androidx.fragment.app.FragmentManager.dispatchStateChange (FragmentManager.java:2977) at androidx.fragment.app.FragmentManager.dispatchActivityCreated (FragmentManager.java:2895) at androidx.fragment.app.F ragment.performActivityCreated (Fragment.java:3143) at androidx.fragment.app.FragmentStateManager.activityCreated (FragmentStateManager.java:579) at androidx.fragment.app.FragmentStateManager.moveToExpectedState (FragmentStateManager.java:264) at androidx.fragment.app.FragmentStore.moveToExpectedState (FragmentStore.java:113) at androidx.fragment.app.FragmentManager.moveToState (FragmentManager.java:1433) at androidx.fragment.app.FragmentManager.dispatchStateChange (FragmentManager.java:2977) at androidx.fragment.app.Frag mentManager.dispatchActivityCreated (FragmentManager.java:2895) at androidx.fragment.app.FragmentController.dispatchActivityCreated (FragmentController.java:263) at androidx.fragment.app.FragmentActivity.onStart (FragmentActivity.java:351) at androidx.appcompat.app.AppCompatActivity.onStart (AppCompatActivity.java:248) at crc643f46942d9dd1fff9.FormsAppCompatActivity.n_onStart at crc643f46942d9dd1fff9.FormsAppCompatActivity.onStart (FormsAppCompatActivity.java:130) at android.app.Instrumentation.callActivityOnStart (Instrumentation.java:147 0) at android.app.Activity.performStart (Activity.java:8154) at android.app.ActivityThread.handleStartActivity (ActivityThread.java:3805) at android.app.servertransaction.TransactionExecutor.performLifecycleSequence (TransactionExecutor.java:221) at android.app.servertransaction.TransactionExecutor.cycleToPath (TransactionExecutor.java:201) at android.app.servertransaction.TransactionExecutor.executeLifecycleState (TransactionExecutor.java:173) at android.app.servertransaction.TransactionExecutor.execute (TransactionExecutor.java:97) at android.app.ActivityThread$H.handleMessage (ActivityThread.java:2345) at android.os.Handler .dispatchMessage (Handler.java:106) at android.os.Looper.loopOnce (Looper.java:233) at android.os.Looper.loop (Looper.java:344) at android.app.ActivityThread.main (ActivityThread.java:8212) at java.lang.reflect.Method.invoke at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run (RuntimeInit.java:584) at com.android.internal.os.ZygoteInit.main (ZygoteInit.java:1034)