android.view.WindowManager$BadTokenException: Unable to add window -- token null is not for an appli

 错误产生： 

Java代码 

private

@Override
protected void
"mcontext="

}

Java代码 

new
.setIcon(android.R.drawable.ic_dialog_alert)
"Warnning")
.setMessage(
"You forget to write the message. Do you want to fill out it ??")
"Yes", positiveListener).setNegativeButton(
"No", negativeListener).create().show();

导致报这个错是在于new AlertDialog.Builder(mcontext)，虽然这里的参数是AlertDialog.Builder(Context context)但我们不能使用getApplicationContext()获得的Context,而必须使用Activity,因为只有一个Activity才能添加一个窗体。 

解决方法：将new AlertDialog.Builder(Context context)中的参数用Activity.this（Activity是你的Activity的名称）来填充就可以正确的创建一个Dialog了。 

Java代码 

new AlertDialog.Builder(MyActivity.this)
.setIcon(android.R.drawable.ic_dialog_alert)
"Warnning")
.setMessage(
"You forget to write the message. Do you want to fill out it ??")
"Yes", positiveListener).setNegativeButton(
"No", negativeListener).create().show();