getting context in AsyncTask

问题

I am trying to get the context in my AsyncTask of the class called Opciones(this class is the only one that call that task) but I don\'t know how to do it, I saw some code like this:

      protected void onPostExecute(Long result) {

    Toast.makeText(Opciones.this,\"Subiendo la foto. ¡Tras ser moderada empezara a ser votada!: \", Toast.LENGTH_LONG).show(); 
}

But it doesn\'t work for me it says: \"No enclosing instance of the type Opciones in scope\"

回答1:

You need to do following things.

when you want to use AsyncTask, extend that in other class say MyCustomTask.
in constructor of new class, pass Context

Example

public class MyCustomTask extends AsyncTask<Void, Void, Long> {

    private Context mContext;

    public MyCustomTask (Context context){
         mContext = context;
    }

    //other methods like onPreExecute etc.
    protected void onPostExecute(Long result) {
         Toast.makeText(mContext,"Subiendo la foto. ¡Tras ser moderada empezara a ser votada!: ", Toast.LENGTH_LONG).show(); 
    }
}

And instantiate class by following.

MyCustomTask task = new MyCustomTask(context);
task.execute(..);

回答2:

Holding a weak reference to the host Activity will prevent memory leaks.

static class MyTask extends AsyncTask<Void, Void, Void> {
    // Weak references will still allow the Activity to be garbage-collected
    private final WeakReference<Activity> weakActivity;

    MyTask(Activity myActivity) {
      this.weakActivity = new WeakReference<>(myActivity);
    }

    @Override
    public Void doInBackground(Void... params) {
      // do async stuff here
    }

    @Override
    public void onPostExecute(Void result) {
      // Re-acquire a strong reference to the activity, and verify
      // that it still exists and is active.
      Activity activity = weakActivity.get();
      if (activity == null
          || activity.isFinishing()
          || activity.isDestroyed()) {
        // activity is no longer valid, don't do anything!
        return;
      }

      // The activity is still valid, do main-thread stuff here
    }
  }

回答3:

Since only one Activity uses this task then just make it an inner class of that Activity

public class Opciones extends Activity
{
     public void onCreate()
     {
         ...
     }

    public class MyTask extends AsyncTask<>
    {
        ...

         protected void onPostExecute(Long result) {
        Toast.makeText(Opciones.this,"Subiendo la foto. ¡Tras ser moderada empezara a ser votada!: ", Toast.LENGTH_LONG).show(); 
     }
}

Then you have access to member variables of the Activity and its Context

回答4:

You can write getApplicationContex(). Or Define global variable.

Activity activity;

And at the onCreate() function

activity = this;

then,

 protected void onPostExecute(Long result) {

    Toast.makeText(activity,"Subiendo la foto. ¡Tras ser moderada empezara a ser votada!: ", Toast.LENGTH_LONG).show(); 
}

来源：https://stackoverflow.com/questions/16920942/getting-context-in-asynctask

标签

android

android-asynctask

toast

android-context