When I run my app on Adnroid Simulator I not have a problem. When I try to run the app on Android Phone I receive error message:

System.InvalidCastException 

Unable to convert instance of type 'Android.Widget.ScrollView' to type 'AndroidX.AppCompat.Widget.Toolbar'.

The debugger stop here:

  base.OnCreate(savedInstanceState);

This is my MainActivity.cs file in Android Project:

using System;
using Android.App;
using Android.Content.PM;
using Android.Runtime;
using Android.OS;

namespace SmartCryptoWorld.Droid
{
    [Activity(Label = "SmartCryptoWorld", Icon = "@mipmap/icon", Theme = "@style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation | ConfigChanges.UiMode | ConfigChanges.ScreenLayout | ConfigChanges.SmallestScreenSize)]
    public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
    {
        protected override void OnCreate(Bundle savedInstanceState)
        {
            TabLayoutResource = Resource.Layout.Tabbar;
            ToolbarResource = Resource.Layout.Toolbar;

            base.OnCreate(savedInstanceState);

            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
            LoadApplication(new App());
        }
        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
        {
            Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

            base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
        }
    }
}

I copy this part of code:

TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;

From another project and I don't know if I really need it. I also copied the folder layout under resources with this files.

Toolbar.axml:

<android.support.v7.widget.Toolbar
xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@ id/toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="?attr/colorPrimary"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

Tabbar.axml:

    <?xml version="1.0" encoding="utf-8"?>
    <android.support.design.widget.TabLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@ id/sliding_tabs"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="?attr/colorPrimary"
    android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    app:tabIndicatorColor="@android:color/white"
    app:tabGravity="fill"
    app:tabMode="fixed" />

Main.axml:

   <?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:orientation="vertical" android:layout_width="match_parent" android:layout_height="match_parent">
    
</LinearLayout>

What Can I do tho fix this error ?

CodePudding user response：

Since you are using the latest Xamarin Forms Activity which uses AndroidX, you need to convert your legacy libraries into AndroidX ones.

For example, replace <android.support.v7.widget.Toolbar/> with <androidx.appcompat.widget.Toolbar/> in the XML layout.

And convert android.support.design.widget.TabLayout to com.google.android.material.tabs.TabLayout