Android Floating Action Button not being recognized

Question

When I look at my code in the editor, nothing seems to be a problem. However, when I run the code on my phone and try to go from one activity to another which features a floating action button, the floating action button cannot find the view by Id despite the ID being exactly the same in both java and XML.

My Java:

package com.test.app.app2_test1;

import android.support.design.widget.FloatingActionButton;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;

public class TermsOfUse extends AppCompatActivity {
    FloatingActionButton mFloatingActionButton;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.terms_of_use);

        mFloatingActionButton = (FloatingActionButton) mFloatingActionButton.findViewById(R.id.terms_back_fab);

        mFloatingActionButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                onBackPressed();
            }
        });
    }
}

My XML:

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.test.app.app2_test1.TermsOfUse"
    android:background="@color/backdrop">

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginBottom="44dp"
        android:orientation="vertical">

    </ScrollView>

    <View
        android:layout_gravity="bottom"
        android:layout_width="match_parent"
        android:layout_height="44dp"
        android:background="@color/colorPrimary"
        android:elevation="4dp"/>

    <android.support.design.widget.FloatingActionButton
        android:id="@+id/terms_back_fab"
        android:layout_gravity="bottom"
        android:layout_width="56dp"
        android:layout_height="56dp"
        android:layout_margin="16dp"
        android:src="@drawable/ic_arrow_back"
        app:pressedTranslationZ="12dp"/>

</android.support.design.widget.CoordinatorLayout>

The message that I get in my console is the following:

Attempt to invoke virtual method 'android.view.View android.support.design.widget.FloatingActionButton.findViewById(int)' on a null object reference

Any help would be appreciated.

Answer 1

You are treating a view as a child of its own!

Replace:

mFloatingActionButton = (FloatingActionButton) mFloatingActionButton.findViewById(R.id.terms_back_fab);

With:

mFloatingActionButton = (FloatingActionButton)findViewById(R.id.terms_back_fab);