android UI(1)-PopupWindow

以弹出音量设置的界面为例，代码如下：

public class MainActivity extends Activity implements View.OnClickListener {    private LinearLayout volset_layout;    private PopupWindow VolsetMenu;    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);        findViewById(R.id.b1).setOnClickListener(this);        volset_layout = new LinearLayout(this);        volset_layout.setOrientation(LinearLayout.HORIZONTAL);        volset_layout.setPadding(5, 5, 5, 5);        volset_layout.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.WRAP_CONTENT,                ViewGroup.LayoutParams.WRAP_CONTENT));        volset_layout.setGravity(Gravity.CENTER);        volset_layout.setBackgroundColor(Color.LTGRAY);        TextView lbl = new TextView(this);        lbl.setText("音量");        lbl.setTextSize(30);        lbl.setGravity(Gravity.CENTER_VERTICAL);        volset_layout.addView(lbl);        final SeekBar seekBar = new SeekBar(this);        seekBar.setLayoutParams(new ViewGroup.LayoutParams(300, ViewGroup.LayoutParams.WRAP_CONTENT));        seekBar.setMax(100);        seekBar.setProgress(50);        volset_layout.addView(seekBar);        VolsetMenu = new PopupWindow(volset_layout, WindowManager.LayoutParams.WRAP_CONTENT,                                                    WindowManager.LayoutParams.WRAP_CONTENT);        VolsetMenu.setBackgroundDrawable(new BitmapDrawable());        VolsetMenu.setOutsideTouchable(true);    }