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

错误产生：

Java代码

private Context mcontext;

@Override

protected void onCreate(Bundle savedInstanceState) {mcontext = getApplicationContext();

System.out.println("mcontext=" + mcontext);

}

private Context mcontext;

@Override
protected void onCreate(Bundle savedInstanceState) {mcontext = getApplicationContext();
System.out.println("mcontext=" + mcontext);

}

Java代码

new AlertDialog.Builder(mcontext)

.setIcon(android.R.drawable.ic_dialog_alert)

.setTitle("Warnning")

.setMessage(

"You forget to write the message. Do you want to fill out it ??")

.setPositiveButton("Yes", positiveListener).setNegativeButton(

"No", negativeListener).create().show();

new AlertDialog.Builder(mcontext)
.setIcon(android.R.drawable.ic_dialog_alert)
.setTitle("Warnning")
.setMessage(
"You forget to write the message. Do you want to fill out it ??")
.setPositiveButton("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)

.setTitle("Warnning")

.setMessage(

"You forget to write the message. Do you want to fill out it ??")

.setPositiveButton("Yes", positiveListener).setNegativeButton(

"No", negativeListener).create().show();

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

问题得以解决！