以下代码不起作用,并引发由NullPointerException引起的RuntimeException

public class ListFilteredActivity extends Activity {
    LinearLayout typeSelector = new LinearLayout(this) ;

    @Override
    public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         ScrollView sv = new ScrollView(this);
         this.setContentView(sv);
         //this.typeSelector = new LinearLayout(this);
         this.typeSelector.setOrientation(LinearLayout.VERTICAL);
         sv.addView(this.typeSelector);
     }

当我在onCreate()中移动this.typeSelection的初始化时,它的效果很好.

    @Override
    public void onCreate(Bundle savedInstanceState) {
       ...
       this.typeSelector = new LinearLayout(this);
       ...
    }

为什么会出现空指针错误？第一段代码中的内联声明在调用构造函数后立即发生,然后onCreate()可以访问该对象,不是吗？