java - MainActivity 不是封闭类

Question

如何解决这个问题？

MainActivity.this is not an enclosing class.

谢谢

public class uploadToServer extends AsyncTask<Void, Void, String> {

protected void onPreExecute() {
    super.onPreExecute();
    ProgressDialog pd= new ProgressDialog(MainActivity.this); //error is here
    pd.setMessage("Wait image uploading!");
    pd.show();
}
}

Answer 1

在AsyncTask的构造函数中，传递Context并在需要时使用它

public class uploadToServer extends AsyncTask<Void, Void, String> {
   private Context mContext;
   public uploadToServer (Context context){
        mContext = context;
   }

   protected void  onPreExecute() {
      super.onPreExecute();
      ProgressDialog pd= new ProgressDialog(mContext); //change is here
      pd.setMessage("Wait image uploading!");
      pd.show();
   }
}

像这样从MainActivity调用，

uploadToServer task = new uploadToServer(getApplicationContext());
task.execute();