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

这个错误是我在看Android SDK文档时，在一个Button的监听器里写了一个自定义的处理条，

代码如下:
  

?

//自定义处理条

        dialog6.setOnClickListener(new OnClickListener() {

 

            @Override

            public void onClick(View v) {

                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();

            }

        });

 

问题出在这句Context mContext =  getApplicationContext(); 

应该写成Activity.this.  Activity所在的Activity.

这是解释http://tech.shantanugoel.com/2010/07/08/badtokenexception-android-dialog-getapplicationcontext.html。