Android覆盖onDraw（）问题

public class MainActivity extends Activity {
    /** Called when the activity is first created. */

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);      
        setContentView(new GraphicView(this));

        TextView mainLabel = (TextView)findViewById(R.id.title);
            mainLabel.setText(\"Android Circle Path\");
    }

    static class GraphicView extends View{
        public GraphicView(Context context){
            super(context);
        }

        @Override
        public void onDraw(Canvas canvas){


        }
    }  
}

<LinearLayout xmlns:android=\"http://schemas.android.com/apk/res/android\"
android:orientation=\"vertical\"
android:layout_width=\"fill_parent\"
android:layout_height=\"fill_parent\"
android:padding=\"30dip\"
>
<LinearLayout
    android:orientation=\"vertical\"
    android:layout_width=\"fill_parent\"
    android:layout_height=\"wrap_content\"
    android:layout_gravity=\"center\"
    android:layout_marginLeft=\"20dip\"
    android:layout_marginRight=\"20dip\">

        <TextView
            android:orientation=\"vertical\"
            android:layout_width=\"fill_parent\"
            android:layout_height=\"wrap_content\"
            android:layout_gravity=\"center\"
            android:layout_marginBottom=\"20dip\"
            android:textSize=\"24.5sp\"
            android:id=\"@+id/title\">
        </TextView>

    </LinearLayout>
</LinearLayout>