Android: ImageSwitcherについて

AndroidでImageSwitcherを使った開発を行っているのですが、
imageSwitcher.setFactory(this)を実行したところ、
以下のエラーが発生してしてしまいました。

解決方法がわからず困っています。
よろしくお願いします。

Java
1public class How_to_use_tour extends Activity implements ViewSwitcher.ViewFactory {
2    TranslateAnimation translateAnimation;
3    AlphaAnimation alphaAnimation;
4    TextView textView_title;
5    TextView textView_content;
6    Button button_next;
7    Button button_back;
8    ImageSwitcher imageSwitcher;
9    int position;
10    @Override
11    protected void onCreate(Bundle savedInstanceState) {
12        super.onCreate(savedInstanceState);
13        setContentView(R.layout.how_to_use_tour);
14        textView_title=(TextView)findViewById(R.id.tour_title);
15        button_next =(Button)findViewById(R.id.tour_next_button);
16        button_back=(Button)findViewById(R.id.tour_back_button);
17        textView_content=(TextView)findViewById(R.id.text_tour_content);
18        imageSwitcher=(ImageSwitcher)findViewById(R.id.image_switcher_tour);
19        imageSwitcher.setFactory(this);
20    }
21    @Override
22    public View makeView() {
23        return null;
24    }
25}

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6540)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at android.widget.ViewSwitcher.obtainView(ViewSwitcher.java:86)
at android.widget.ViewSwitcher.setFactory(ViewSwitcher.java:104)
at com.example.shion.bunnkasai.How_to_use_tour.onCreate(How_to_use_tour.java:36)
at android.app.Activity.performCreate(Activity.java:6980)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6540)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
07-18 08:08:48.127 9802-9802/com.example.shion.bunnkasai E/UncaughtException: java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.shion.bunnkasai/com.example.shion.bunnkasai.How_to_use_tour}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6540)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.view.View.getLayoutParams()' on a null object reference
at android.widget.ViewSwitcher.obtainView(ViewSwitcher.java:86)
at android.widget.ViewSwitcher.setFactory(ViewSwitcher.java:104)
at com.example.shion.bunnkasai.How_to_use_tour.onCreate(How_to_use_tour.java:36)
at android.app.Activity.performCreate(Activity.java:6980)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6540)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)