Unable to add window -- token null is not for an application

原文出处：http://blog.csdn.net/wsz1z154/article/details/7724912

在创建一个Dialog时，发生的错误：

Unable to add window -- token null is not for an application

 AlertDialog.Builder builder;
 AlertDialog alertDialog;
 Context mContext = getApplicationContext();
 LayoutInflater inflater = (LayoutInflater) mContext.getSystemService(LAYOUT_INFLATER_SERVICE);
 View layout = inflater.inflate(R.layout.custom_dialog, (ViewGroup)findViewById(R.id.layout_root));

 TextView text = (TextView) layout.findViewById(R.id.text);
 text.setText("Hello, this is a custom dialog!");
 ImageView image = (ImageView) layout.findViewById(R.id.image);
 image.setImageResource(R.drawable.icon);
 builder = new AlertDialog.Builder(mContext);
 builder.setView(layout);
 alertDialog = builder.create();
 alertDialog.show();

查询SDK帮助文档：

Return the context of the single, global Application object of the current process. This generally should only be used if you need a Context whose lifecycle is separate from the current context, that is tied to the lifetime of the process rather than the current component.

把这句Context mContext =  getApplicationContext(); 

改成Activity.this即可

详见新浪博文http://blog.sina.com.cn/s/blog_4b93170a0102e123.html

代码中出现如下错误：

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

分析：

问题在于new AlertDialog.Builder(Context)，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的Context对象，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的Context对象即可

该问题的具体原因可详见：http://blog.csdn.net/lmj623565791/article/details/40481055