findViewById возвращает null-почему?

Я создал пользовательский вид Game4, который расширяет LinearLayout. Когда я попытался найти их, это поле и вернуло null (а затем nullPointerException, а затем crash/!!)
Это activity_play_game.xml:

<ScrollView

android:id="@+id/scrollView1"

android:layout_width="match_parent"

android:layout_height="wrap_content"

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

xmlns:tools="http://schemas.android.com/tools"

tools:context="com.example.sortthegraph.PlayGameActivity"

tools:ignore="MergeRootFrame" >



<LinearLayout

    android:id="@+id/container"

    android:layout_width="match_parent"

    android:layout_height="wrap_content"

    android:orientation="vertical" >



    <com.example.sortthegraph.Game_4 // A custom View extends LinearLayout

        android:id="@+id/game4"

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:gravity="center" >

    </com.example.sortthegraph.Game_4>



    <View

        android:layout_width="match_parent"

        android:layout_height="1dip"

        android:background="#000000" />



    <Spinner

        android:id="@+id/spinner1"

        android:layout_width="match_parent"

        android:layout_height="wrap_content" />



</LinearLayout>

Это моя функция OnCreate:

@Override

protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);

    setContentView(R.layout.activity_play_game);        

    tempGame = (Game_4) findViewById(R.id.game4); // ?? Why null ??

Это конструкторы Game_4:

public class Game_4 extends LinearLayout {

public Game_4(Context context, AttributeSet attrs) {

    this(context);

}

public Game_4(Context context) {

    super(context);



    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);

    inflater.inflate(R.layout.game_4_layout, this, true);

    this.setWillNotDraw(false);

}

Game_4_layout.xml:

<?xml version="1.0" encoding="utf-8"?>

<TableLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="wrap_content"

    android:orientation="vertical"

    android:paddingTop="20dp"

    android:paddingBottom="25dp"

    android:layout_marginLeft="15dip"

    android:layout_marginRight="15dip"

    android:gravity="center" >



<TableRow

    android:id="@+id/tableRow1"

    android:layout_width="wrap_content"

    android:layout_height="wrap_content" >



    <View android:layout_width="0dip"

        android:layout_height="match_parent"

        android:layout_weight="1" />



    <com.example.sortthegraph.BackButton

        android:id="@+id/backButton1"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_marginBottom="20dp" >

    </com.example.sortthegraph.BackButton>



    <View android:layout_width="0dip"

        android:layout_height="match_parent"

        android:layout_weight="1" />



</TableRow>



    <TableRow

        android:id="@+id/tableRow2"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:layout_gravity="center"

        android:layout_marginBottom="20dip"

        android:layout_marginTop="20dip" >



        <com.example.sortthegraph.BackButton

            android:id="@+id/backButton2"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content" >

        </com.example.sortthegraph.BackButton>



        <View 

            android:layout_width="0dip"

            android:layout_height="match_parent"

            android:layout_weight="1" />



        <com.example.sortthegraph.BackButton

            android:id="@+id/backButton3"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content" >

        </com.example.sortthegraph.BackButton>



    </TableRow>



    <TableRow

        android:id="@+id/tableRow3"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content" >



        <View android:layout_width="0dip"

        android:layout_height="match_parent"

        android:layout_weight="1" />



        <com.example.sortthegraph.BackButton

            android:id="@+id/backButton4"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:layout_marginTop="20dp" >

        </com.example.sortthegraph.BackButton>



        <View android:layout_width="0dip"

        android:layout_height="match_parent"

        android:layout_weight="1" />



    </TableRow>