[Solved] android studio : findViewById return NULL Pointer [duplicate]

by 


<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="bd2c.bd2c_appdemo.MainActivity">

<TextView
    android:id="@+id/principal"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/app_text" />
</RelativeLayout>

This is your fixed layout select all copy that and go to your layout select all and paste this. Bingo 🙂

solved android studio : findViewById return NULL Pointer [duplicate]