自定义Dialog后如何 设置setTitle啊

public class MainActivity extends Activity {    /** Called when the activity is first created. */    Dialog dialog;            public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);                    //new一个Dialog对象，在实例化的时候传入主题        dialog = new MyDialog(MainActivity.this, R.style.MyDialog);        //设置它的ContentView        dialog.setContentView(R.layout.dialog);         // 设置对话框关闭之前对话框之外的区域不可点击          dialog.setCanceledOnTouchOutside(false);          dialog.setTitle("你在哪？");                        dialog.show();          }

public class MyDialog extends AlertDialog {    Context context;    public MyDialog(Context context) {        super(context);        // TODO Auto-generated constructor stub        this.context = context;    }    public MyDialog(Context context, int theme){        super(context, theme);        this.context = context;    }    @Override    protected void onCreate(Bundle savedInstanceState) {        // TODO Auto-generated method stub        super.onCreate(savedInstanceState);        this.setContentView(R.layout.dialog);        ImageView imageview = (ImageView)findViewById(R.id.imageviewClose);        imageview.setOnClickListener(new View.OnClickListener() {                        public void onClick(View v) {                            cancel();            }        });    }

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent"    android:orientation="vertical"    android:background="#FFFFFF" >    <RelativeLayout        android:layout_width="fill_parent"        android:layout_height="fill_parent"        android:orientation="horizontal" >        <TextView            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:paddingLeft="12dip"            android:paddingTop="6dip"            android:textColor="#050505"            android:textSize="15dp"            android:text="用户"            />        <ImageView            android:id="@+id/imageviewClose"            android:layout_width="wrap_content"            android:layout_height="wrap_content"            android:layout_alignParentRight="true"            android:layout_alignParentTop="true"            android:layout_marginRight="15dp"            android:src="@drawable/close" />    </RelativeLayout>    <View        android:layout_width="fill_parent"        android:layout_height="2px"         android:layout_marginTop="5dp"                  android:background="@drawable/mypic"    />    </LinearLayout>