Android報錯：WindowManager$BadTokenException: Unable to add window -- window has already been added

很久之前測試通過的代碼，現在手機升級了Android7.0后一運行就崩潰，報出這樣的錯誤，具體錯誤如下：

Process: com.example.sho.android_anti_theft, PID: 26807            
android.view.WindowManager$BadTokenException: Unable to add window -- window android.view.ViewRootImpl$W@363f7b1 has already been added
 at android.view.ViewRootImpl.setView(ViewRootImpl.java:691)
 at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:342)
 at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:94)
 at android.widget.Toast$TN.handleShow(Toast.java:434)
 at android.widget.Toast$TN$2.handleMessage(Toast.java:345)
 at android.os.Handler.dispatchMessage(Handler.java:102)
 at android.os.Looper.loop(Looper.java:154)
 at android.app.ActivityThread.main(ActivityThread.java:6119)
 at java.lang.reflect.Method.invoke(Native Method)
 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

從報錯信息中，我得出這樣一個結論：

在Android6.0以前，使用windowManager添加一個懸浮窗時，我使用的懸浮窗類型是TYPE_TOAST，即
params.type = WindowManager.LayoutParams.TYPE_TOAST;
windowManager.addView(contentView, params);
但是系統升級Android7.0后，就會報ndroid.view.WindowManager$BadTokenException: Unable to add window -- window android.view.ViewRootImpl$W@363f7b1 has already been added
的錯，具體意思是Toast已經被添加到窗口中，所以這時候我們可以把TYPE_TOAST換成TYPE_PHONE，這樣就可以顯示懸浮窗了，程序也不會crash。

這里附上添加懸浮窗的代碼，僅供參考：

WindowManager windowManager = (WindowManager) getSystemService(WINDOW_SERVICE);		
WindowManager.LayoutParams params = new     
WindowManager.LayoutParams();
params.type = WindowManager.LayoutParams.TYPE_PHONE;
params.format = PixelFormat.RGBA_8888;
params.gravity = Gravity.LEFT | Gravity.TOP;
params.flags = WindowManager.LayoutParams.FLAG_NOT_FOCUSABLE;
params.width = windowManager.getDefaultDisplay().getWidth();
params.height = windowManager.getDefaultDisplay().getHeight();
params.x = 0;
params.y = 0;
windowManager.addView(contentView, params);      

//這里要的contentview需要自己定義，而且添加懸浮窗需要動態申請懸浮窗權限。