findViewById中NullPointerException的错误

* There are two methods almost all subclasses of Activity will implement:
*
* <ul>
*     <li> {@link #onCreate} is where you initialize your activity.  Most
*     importantly, here you will usually call {@link #setContentView(int)}
*     with a layout resource defining your UI, and using {@link #findViewById}
*     to retrieve the widgets in that UI that you need to interact with
*     programmatically.
*
*     <li> {@link #onPause} is where you deal with the user leaving your
*     activity.  Most importantly, any changes made by the user should at this
*     point be committed (usually to the
*     {@link android.content.ContentProvider} holding the data).
* </ul>

2.

private CharSequence mTitle;
private int mTitleColor = 0;
final FragmentManagerImpl mFragments = new FragmentManagerImpl();
final FragmentContainer mContainer = new FragmentContainer() {
@Override
public View findViewById(int id) {
return Activity.this.findViewById(id);
}
};

3.

/**
* Called when the activity is starting.  This is where most initialization
* should go: calling {@link #setContentView(int)} to inflate the
* activity's UI, using {@link #findViewById} to programmatically interact
* with widgets in the UI, calling
* {@link #managedQuery(android.net.Uri , String[], String, String[], String)} to retrieve
* cursors for data being displayed, etc.

4.

/**
* Finds a view that was identified by the id attribute from the XML that
* was processed in {@link #onCreate}.
*
* @return The view if found or null otherwise.
*/
public View findViewById(int id) {
return getWindow().findViewById(id);
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/LinearLayout"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
</LinearLayout>
[xml]
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
</LinearLayout>