java.lang.ClassCastException：android.widget.LinearLayout无法强制转换为android.support.v7.widget.Toolbar

Question

I was trying to add a shadow to the toolbar following this example over here https://stackoverflow.com/a/26904102/4273056

My toolbar in activity

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

   Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);
}

This is the xml file where I added the toolbar

<LinearLayout
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="top"
android:orientation="vertical"
xmlns:android="http://schemas.android.com/apk/res/android">

<android.support.v7.widget.Toolbar            
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/primaryColor"
android:paddingTop="@dimen/app_bar_top_padding"
app:popupTheme="@style/ThemeOverlay.AppCompat.Dark"
app:theme="@style/MyCustomToolBarTheme">

</android.support.v7.widget.Toolbar>
<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <!-- **** Place Your Content Here **** -->

    <View
        android:layout_width="match_parent"
        android:layout_height="5dp"
        android:background="@drawable/shadow" />
</FrameLayout>
</LinearLayout>

I get this in the logcat java.lang.ClassCastException: android.widget.LinearLayout cannot be cast to android.support.v7.widget.Toolbar

How can I get rid of this error?

Answer 1

Add the id attribute in your Toolbar and check if you have another element with the same id.

<android.support.v7.widget.Toolbar 
   android:id="@+id/toolbar"
   .....
/>

Also it is better:

 Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    if (toolbar != null)
        setSupportActionBar(toolbar);