How to use databasehelper class in an asynctask class working on a different class

问题

Hi everybody I was stuck at a point, the problem is that I have three classes shown below and I want to instantiate my DatabaseHelper class in AsyncTask class. Could you please help, how can I get context in AsyncTask class?

Problem Solved

1. MainActivity class

   public class MainActivity extends Activity {
   ...
   FetchData fetchData = new FetchData();
   fetchData.execute();
   ...
   }
   

2. DatabaseHelper

   public class DatabaseHelper extends SQLiteOpenHelper {
   ....
   public DatabaseHelper(Context context) {
   super(context, DATABASE_NAME, null, DATABASE_VERSION);
   ....
   }
   

3. FetchData class

   public class FetchData extends AsyncTask<String, String, String> {
   ....
   DatabaseHelper db = new DatabaseHelper(); //need context here!!!
   ....
   }
   

#

Thanks to Kasra, I create a fourh class and use it in MainActivity before calling AsyncTask

4. ContextStatic class

   public class ContextStatic {
   private static Context mContext;
   
   public static Context getmContext() {
       return mContext;
   }
   public static void setmContext(Context mContext) {
       ContextStatic.mContext = mContext;
   }
   }
   

Updated MainActivity class

    public class MainActivity extends Activity {
    ...
    ContextStatic.setmContext(this);
    FetchData fetchData = new FetchData();
    fetchData.execute();
    ...
    }

回答1:

Try this:

 private class FetchData extends AsyncTask<Context, Void, Void> {
     protected Long doInBackground(Context... c) {
         Context myContext = c[0];
// Do your things here....
     }


     protected void onPostExecute() {
// Insert your post execute code here
     }
 }

You can call this AsyncTask by the following line - assuming you are in an activity:

 new FetchData().execute(this);

---

if You cannot change your AsyncTask deceleration, then you can try using a static variable - although it is not as efficient and pretty as AsyncTask deceleration. Try this:

Class myStatic{
private  static Context mContext;


static public void setContext(Context c);
mContext = c;
}

static public Context getContext(){
return mContext;
}

}

and in your main code, before you call AsyncTask, call this:

myStatic.setContext(this);

in your doInBackground method of your AsyncTask, add this:

Context myContext = myStatic.getContext();

来源：https://stackoverflow.com/questions/28267764/how-to-use-databasehelper-class-in-an-asynctask-class-working-on-a-different-cla