Android --- 刚刚进入 Activity 页面的时候无法打开对话框，报错 Unable to add window -- token null is not valid； is your

报错如下：

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.gxuwz.yixin, PID: 29723
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.gxuwz.yixin/com.gxuwz.yixin.activity.edit.EditAddressActivity}: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3315)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3464)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2051)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:239)
        at android.app.ActivityThread.main(ActivityThread.java:7604)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:953)
     Caused by: android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
        at android.view.ViewRootImpl.setView(ViewRootImpl.java:989)
        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:387)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:97)
        at android.widget.PopupWindow.originalInvokePopup(PopupWindow.java:1590)
        at android.widget.PopupWindow.invokePopup(PopupWindow.java:1575)
        at android.widget.PopupWindow.showAtLocation(PopupWindow.java:1345)
        at android.widget.PopupWindow.showAtLocation(PopupWindow.java:1311)
        at com.gxuwz.yixin.activity.edit.EditAddressActivity.onCreate(EditAddressActivity.java:46)
        at android.app.Activity.performCreate(Activity.java:7916)
        at android.app.Activity.performCreate(Activity.java:7903)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1306)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3290)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3464) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2051) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:239) 
        at android.app.ActivityThread.main(ActivityThread.java:7604) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:539) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:953) 

主要就这句：Unable to add window -- token null is not valid; is your activity running?

最终的意思就是，你的 Activity 视图还没有加载完，你就要在此 Activity 上添加对话框是不可以的 因为每一个对话框都要依附于一个 Activity，所以我们要用到一个判断 Activity 加载完的方法，在 Activity 加载完毕之后调用对话框即可

@Override
    public void onWindowFocusChanged(boolean hasFocus)
    {
        if (hasFocus) {
           // 调用对话框部分
        }
    }

但是有的小伙伴会发现，这个对话框会一直跳出，点了关闭又跳出，重复执行，所以我加了个计数器来判断。

int count = 0;
@Override
    public void onWindowFocusChanged(boolean hasFocus)
    {
        if (hasFocus && count == 0) {
        	count++;
           // 调用对话框部分
        }
    }

这样一来，只有第一次进入的时候会显示对话框，其余的时候都不会弹出了