BadTokenException: Unable to add

 android.view.WindowManager$BadTokenException: Unable to add window -- token null is not valid; is your activity running?
        at android.view.ViewRootImpl.setView(ViewRootImpl.java:791)
        at android.view.WindowManagerGlobal.addView(WindowManagerGlobal.java:356)
        at android.view.WindowManagerImpl.addView(WindowManagerImpl.java:93)
        at android.app.Dialog.show(Dialog.java:330)
        at com.example.myapplication.ToastActivity.onCreate(ToastActivity.java:22)
        at android.app.Activity.performCreate(Activity.java:7003)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1230)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2899)

代码如下

final Dialog dialog = new Dialog(getApplicationContext());
        dialog.setContentView(R.layout.dialog_show);
        dialog.show();

原因分析：dialog的context必须是Acitvity的context；