Android Custom Dialog錯誤Unable to add window — token null is not for an application

 

按照Android手冊上的自訂Dialog章節學習使用自訂Dialog是出現如下錯誤：

android.view.WindowManager$BadTokenException: Unableto add window--tokennullisnotforan application

手冊上代碼邏輯如下：

LayoutInflater inflater = (LayoutInflater)getApplicationContext().getSystemService(LAYOUT_INFLATER_SERVICE);

View layout = inflater.inflate(R.layout.custom_dialog,

(ViewGroup)findViewById(R.id.layout_root));

TextView  tv = (TextView)layout.findViewById(R.id.custom_text);

tv.setText("Hello, this is a custom dialfo");

ImageView iv = (ImageView)layout.findViewById(R.id.custom_image);

iv.setImageResource(R.drawable.icon);

builder = new AlertDialog.Builder(getApplicationCOntext());

builder.setView(layout);

dialog = builder.create();

將紅色標記語句改為builder = new AlertDialog.Builder(this);

錯誤原因：

You need to use your Activty as the Context for the Dialog not the Application.

Android is looking for a view to display the Dialog in and the Application does not have one but yourActivity will. The Application is an object which ties your app together and has a Context as it knows about which locale you're running in and so on, but
it relies on Activities to display things to the user.