android - "android.view.WindowManager$BadTokenException: Unable to add window"上 buider.show()

Question

从我的主 activity 中，我需要调用一个内部类，并且在该类中的一个方法中，我需要显示 AlertDialog。关闭后，按下 OK 按钮后，转到 Google Play 购买。

大多数情况下一切正常，但对于少数用户来说，它在 builder.show() 上崩溃，我可以看到 "android.view.WindowManager$BadTokenException:无法从崩溃日志中添加窗口。请提出建议。

我的代码差不多是这样的:

public class classname1 extends Activity{

  public void onCreate(Bundle savedInstanceState) {
    this.requestWindowFeature(Window.FEATURE_NO_TITLE);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.<view>); 

    //call the <className1> class to execute
  }

  private class classNamename2 extends AsyncTask<String, Void, String>{

    protected String doInBackground(String... params) {}

    protected void onPostExecute(String result){
      if(page.contains("error")) 
      {
        AlertDialog.Builder builder = new AlertDialog.Builder(classname1.this);
        builder.setCancelable(true);
        builder.setMessage("");
        builder.setInverseBackgroundForced(true);
        builder.setNeutralButton("Ok",new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton){
            dialog.dismiss();
            if(!<condition>)
            {
              try
              {
                String pl = ""; 

                mHelper.<flow>(<class>.this, SKU, RC_REQUEST, 
                  <listener>, pl);
              }

              catch(Exception e)
              {
                e.printStackTrace();
              }
            }  
          }
        });

        builder.show();
      }
    }
  }
}

我还在另一个警报中看到了错误，我没有转发到任何其他 activity。很简单:

AlertDialog.Builder builder = new AlertDialog.Builder(classname1.this);
    builder.setCancelable(true);

    //if successful
    builder.setMessage(" ");
    builder.setInverseBackgroundForced(true);
    builder.setNeutralButton("Ok",new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int whichButton){
            // dialog.dismiss();
                   }
    });
    builder.show();
}

Answer 1

android.view.WindowManager$BadTokenException: Unable to add window"

问题:

This exception occurs when the app is trying to notify the user from the background thread (AsyncTask) by opening a Dialog.

If you are trying to modify the UI from background thread (usually from onPostExecute() of AsyncTask) and if the activity enters finishing stage i.e.) explicitly calling finish(), user pressing home or back button or activity clean up made by Android then you get this error.

原因:

The reason for this exception is that, as the exception message says, the activity has finished but you are trying to display a dialog with a context of the finished activity. Since there is no window for the dialog to display the android runtime throws this exception.

解决方案:

Use isFinishing() method which is called by Android to check whether this activity is in the process of finishing: be it explicit finish() call or activity clean up made by Android. By using this method it is very easy to avoid opening dialog from background thread when activity is finishing.

Also maintain a weak reference for the activity (and not a strong reference so that activity can be destroyed once not needed) and check if the activity is not finishing before performing any UI using this activity reference (i.e. showing a dialog).

例如。

private class chkSubscription extends AsyncTask<String, Void, String>{

  private final WeakReference<login> loginActivityWeakRef;

  public chkSubscription (login loginActivity) {
    super();
    this.loginActivityWeakRef= new WeakReference<login >(loginActivity)
  }

  protected String doInBackground(String... params) {
    //web service call
  }

  protected void onPostExecute(String result) {
    if(page.contains("error")) //when not subscribed
    {
      if (loginActivityWeakRef.get() != null && !loginActivityWeakRef.get().isFinishing()) {
        AlertDialog.Builder builder = new AlertDialog.Builder(login.this);
        builder.setCancelable(true);
        builder.setMessage(sucObject);
        builder.setInverseBackgroundForced(true);

        builder.setNeutralButton("Ok",new DialogInterface.OnClickListener() {
          public void onClick(DialogInterface dialog, int whichButton){
            dialog.dismiss();
          }
        });

        builder.show();
      }
    }
  }
}

更新:

窗口标记:

As its name implies, a window token is a special type of Binder token that the window manager uses to uniquely identify a window in the system. Window tokens are important for security because they make it impossible for malicious applications to draw on top of the windows of other applications. The window manager protects against this by requiring applications to pass their application's window token as part of each request to add or remove a window. If the tokens don't match, the window manager rejects the request and throws a BadTokenException. Without window tokens, this necessary identification step wouldn't be possible and the window manager wouldn't be able to protect itself from malicious applications.

 真实场景:

When an application starts up for the first time, the ActivityManagerService creates a special kind of window token called an application window token, which uniquely identifies the application's top-level container window. The activity manager gives this token to both the application and the window manager, and the application sends the token to the window manager each time it wants to add a new window to the screen. This ensures secure interaction between the application and the window manager (by making it impossible to add windows on top of other applications), and also makes it easy for the activity manager to make direct requests to the window manager.