Android中如何获取手机屏幕大小

public     class    TestActivity extends Activity {

     private    TextView tv;
     private    Button btn;

     //获取手机 屏幕分辨率的类
      private    DisplayMetrics dm;

     public     void    onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        tv = (TextView)findViewById(R.id.tv);
        btn = (Button)findViewById(R.id.btnOK);
        btn.setOnClickListener( new    View.OnClickListener() {

           public     void    onClick(View v) {
              dm =  new    DisplayMetrics();
          getWindowManager().getDefaultDisplay().getMetrics(dm);
                   //获得手机 的宽度和高度像素单位为px
          String strPM =  "手机 屏幕分辨率为:"   + dm.widthPixels+ "* "  +dm.heightPixels;
          tv.setText(strPM);
            }
        });
    }

}