WindowManager  ：懸浮層   它的View顯示在整個系統的最頂層，在設定屬性後，此View則可以存在手機主視窗上

給windowManager新增overlay這個檢視

LayoutInflater inflater = LayoutInflater.from(this);
overlay = (TextView) inflater.inflate(R.layout.overlay, null);
overlay.setVisibility(View.INVISIBLE);
WindowManager.LayoutParams lp = new WindowManager.LayoutParams(
        LayoutParams.WRAP_CONTENT
 
, LayoutParams.WRAP_CONTENT,
WindowManager.LayoutParams.TYPE_APPLICATION,
WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE
| WindowManager.LayoutParams.FLAG_NOT_TOUCHABLE,
PixelFormat.TRANSLUCENT);
windowManager = (WindowManager)this.getSystemService(Context.WINDOW_SERVICE);
windowManager.addView(overlay
 
, lp);

但是當我關閉此activity時會報如下錯誤：

   12801-12801/com.wjf.fw.mybus E/WindowManager﹕ Activity com.wjf.fw.mybus.ChangeCityActivity has leaked window android.support.v7.widget.AppCompatTextView{4279d760 I.ED.... ......I. 0,0-130,186} that was originally added here
    android.view.WindowLeaked: Activity com.wjf.fw.mybus.ChangeCityActivity has leaked window android.support.v7.widget.AppCompatTextView{4279d760 I.ED....

雖然此錯誤不影響應用使用，但畢竟是錯誤，應該去解決：當銷燬activity時應去掉WindowManager的檢視

@Override
protected void onDestroy() {
    super.onDestroy();
windowManager.removeView(overlay);
}