title: having problem with the method findViewById
body: <p>Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference
  at com.example.azerhi.My_List_View.onCreate(My_List_View.java:26)</p>
  <p>this is the xml</p>
  <pre><code>      android:id=&quot;@+id/walidlistee&quot;
        android:layout_width=&quot;409dp&quot;
        android:layout_height=&quot;729dp&quot;
        android:layout_alignParentTop=&quot;true&quot;
        android:layout_alignParentEnd=&quot;true&quot;
        android:layout_alignParentRight=&quot;true&quot;
        android:layout_marginTop=&quot;0dp&quot;
        android:layout_marginEnd=&quot;2dp&quot;
        android:layout_marginRight=&quot;2dp&quot;
        app:layout_constraintBottom_toBottomOf=&quot;parent&quot;
        app:layout_constraintEnd_toEndOf=&quot;parent&quot;
        app:layout_constraintStart_toStartOf=&quot;parent&quot;
        app:layout_constraintTop_toTopOf=&quot;parent&quot; /&gt;```
  
  and this is the code 
  walidList.findViewById(R.id.walidlistee);
  </code></pre>