关于WindowManager$BadTokenException: Unable to add window异常

我在自定义View里面添加了一个动画，监听动画结束时弹出一个dialog对话框，但是遇到一个问题，就是当动画开始播放尚未结束时，我直接关掉App，会出现一个异常，这个异常大概意思是Activity已经销毁，或者没有创建，不能在上面加一个窗口

11-24 14:31:24.641 29357-29357/com.yaodan.shaketerrace E/AndroidRuntime: FATAL EXCEPTION: main
                                                                         Process: com.yaodan.shaketerrace, PID: 29357
                                                                         android.view.WindowManager$BadTokenException: Unable to add window -- token android.os.BinderProxy@625e191 is not valid; is your activity running?
                                                                             at android.view.ViewRootImpl.setView(ViewRootImpl.java:575)
                                                                             at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:313)
                                                                             at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:86)
                                                                             at android.app.Dialog.show(Dialog.java:322)
                                                                             at android.support.v7.app.AlertDialog$Builder.show(AlertDialog.java:949)
                                                                             at com.yaodan.shaketerrace.animator.FllowerAnimation.showDialog(FllowerAnimation.java:337)
                                                                             at com.yaodan.shaketerrace.animator.FllowerAnimation$1.onAnimationEnd(FllowerAnimation.java:300)
                                                                             at android.animation.ValueAnimator.endAnimation(ValueAnimator.java:1239)
                                                                             at android.animation.ValueAnimator$AnimationHandler.doAnimationFrame(ValueAnimator.java:766)
                                                                             at android.animation.ValueAnimator$AnimationHandler$1.run(ValueAnimator.java:801)
                                                                             at android.view.Choreographer$CallbackRecord.run(Choreographer.java:860)
                                                                             at android.view.Choreographer.doCallbacks(Choreographer.java:672)
                                                                             at android.view.Choreographer.doFrame(Choreographer.java:605)
                                                                             at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:846)
                                                                             at android.os.Handler.handleCallback(Handler.java:739)
                                                                             at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                             at android.os.Looper.loop(Looper.java:148)
                                                                             at android.app.ActivityThread.main(ActivityThread.java:5441)
                                                                             at java.lang.reflect.Method.invoke(Native Method)
                                                                             at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738)
                                                                             at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628)

我是这样解决的，当我弹出dialog弹出时，我会判断当前Activity是否销毁，但是由于在自定义View里我没能找到判断Activity是否销毁的办法，所以我就判断是否有当前窗口的焦点，如果有，我才显示dialog

if(hasWindowFocus()) {
     builder.show();
}