Android: Service中创建窗口显示

WindowManager.LayoutParams：

int TYPE_SYSTEM_ALERT  Window type: system window, such as low power alert.（系统窗体，例如低电量警告提示框）
int TYPE_SYSTEM_OVERLAY  Window type: system overlay windows, which need to be displayed on top of everything else.（系统覆盖窗体，哪个需要显示在最前的）

TYPE_SYSTEM_ALERT跟TYPE_SYSTEM_OVERLAY的区别

system_alert窗口可以获得焦点，响应操作

system_overlay窗口显示的时候焦点在后面的Activity上，仍旧可以操作后面的Activity

清单文件manifest中需要相应的permission

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />  
    <uses-permission android:name="android.permission.SYSTEM_OVERLAY_WINDOW" />

以下两种方式显示出来的窗口都不会激发当前Activity的onPause()事件。

1. Seivece 创建窗体

 private void showSystemDialog() {
     /* create ui dialog */
     View v = View.inflate(mContext, R.layout.serveice_dialog, null);
     AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
     alertDialog.setView(v);
     dialog = alertDialog.create();
     dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_ALERT);
     //dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_SYSTEM_OVERLAY);
     dialog.show();
     **** 注意dialog 在执行show方法之后，才能调整dialog的大小以及更新数据 ****
     /* set size & pos */
     WindowManager.LayoutParams lp = dialog.getWindow().getAttributes();
     WindowManager wm = (WindowManager) getSystemService(WINDOW_SERVICE);
     Display display = wm.getDefaultDisplay();
     if (display.getHeight() > display.getWidth()) {
         //lp.height = (int) (display.getHeight() * 0.5);
         lp.width = (int) (display.getWidth() * 1.0);
     } else {
         //lp.height = (int) (display.getHeight() * 0.75);
         lp.width = (int) (display.getWidth() * 0.5);
     }
     d.getWindow().setAttributes(lp);  

     /* update ui data */
     lv = (ListView) d.getWindow().findViewById(R.id.listview);
     SimpleAdapter adapter = new SimpleAdapter(mContext, getListData(), R.layout.list_item,
                             new String[]{"item_text", "item_img"},
                             new int[]{R.id.item_text, R.id.item_img});
     lv.setAdapter(adapter);           

     /* set listener */
     lv.setOnItemClickListener(new OnItemClickListener() {
         public void onItemClick(AdapterView<?> parent, View view, int pos,
                 long id) {
             d.dismiss();
         }
     });       

 }  

2. 直接使用WindowManager.addView()在后台直接显示窗口

  LayoutInflater inflater = (LayoutInflater)getSystemService(Context.LAYOUT_INFLATER_SERVICE);
  mDesktopLayout = inflater.inflate(R.layout.volume_panel, null);
  // 取得系统窗体
  mWindowManager = (WindowManager) getApplicationContext().getSystemService(WINDOW_SERVICE);
  // 窗体的布局样式
  mLayoutParams = new WindowManager.LayoutParams();
  // 设置窗体显示类型――TYPE_SYSTEM_ALERT(系统提示)
  mLayoutParams.type = WindowManager.LayoutParams.TYPE_SYSTEM_ALERT;
  // 设置窗体焦点及触摸：
  // FLAG_NOT_FOCUSABLE(不能获得按键输入焦点)
  mLayoutParams.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
  // 设置显示的模式
  mLayoutParams.format = PixelFormat.RGBA_8888;
  // 设置对齐的方法
  mLayoutParams.gravity = Gravity.TOP | Gravity.LEFT;
  // 设置窗体宽度和高度
  mLayoutParams.width = WindowManager.LayoutParams.WRAP_CONTENT;
  mLayoutParams.height = WindowManager.LayoutParams.WRAP_CONTENT;
  // 设置窗体显示的位置，否则在屏幕中心显示
  mLayoutParams.x = 50;
  mLayoutParams.y = 50;
  mWindowManager.addView(mDesktopLayout, mLayoutParams);