Namespace 'app' not bound, in Android Studio with external lib from Maven

Question

I get Namespace 'app' not bound whenever I try to specify the properties for the external libs UI elements.

        <LinearLayout             android:id="@+id/card_database"             android:layout_width="match_parent"             android:layout_height="match_parent"             android:clickable="true"             android:onClick="dbclicked"             android:orientation="horizontal"             android:background="#ffff7f31"             >              <ImageView                 android:id="@+id/img_database"                 android:layout_width="wrap_content"                 android:layout_height="wrap_content"                 android:src="@drawable/db"                 />              <TextView                 android:id="@+id/txt_database"                 android:layout_width="match_parent"                 android:layout_height="match_parent"                 android:gravity="center_vertical"                 android:paddingStart="15dp"                 android:text="@string/db"                 android:textColor="#ffffff"                 android:textSize="20sp"                 android:autoText="false" />         </LinearLayout>         </com.balysv.materialripple.MaterialRippleLayout> 

compile 'com.balysv:material-ripple:1.0.0' is used in build.gradle and I am running the latest version of the Android Studio with updates.

Answer 1

Add

xmlns:app="http://schemas.android.com/apk/res-auto" 

to your root element

Answer 2

Simply select the error (touch the error by mouse) and press. "ALT+ENTER" it will automatically solve the error.