从AsyncTask调用不同的活动方法

Question

I have a MainActivity , SecondaryActivity and an AsyncTask class.
MainActivity has a method called doSomething()

I call the AsyncTask from MainActivity like this:

new asyncTask(MainActivity.this).execute();

Which means I can reference the MainActivity in my onPostExecute

@Override
protected void onPostExecute(Boolean result){
    super.onPostExecute(result);
    # activity is defined as this.activity
    activity.doSomething();       
}

How can I call the AsyncTask from my SecondaryActivity in a similar manner, because I'd need a reference to my MainActivity to access its methods?

EDIT: I would want the doSomething() to be called at all times. So even if it's from SecondActivity, once it finishes its background operation -> doSomething()

The method I'm calling refreshes the screen of MainActivity to show data changes. Secondary activity only calls the AsyncTask when it is being paused/stopped/destroyed but currently the Asynctask finishes after MainActivity has started and so the changes aren't visible.

Answer 1

I think your AsyncTask in nested in the MainActivity currently. Its better you put it in separate class. Whatever parameter is required by it pass it in its constructor. Let both your activity implement the same interface. Something like this

class MainActivity/SecondaryActivity implements DoSomethingListener {
     void doSomething() {
     }
}

Also pass your activity reference to AsyncTask in the constructor.

Finally onPostExecute since you have reference to either MainActivity or Secondary Activity. Call activity.doSomething.

Answer 2

I guess you want to update something in MainActivity based on the result of the AsyncTask called from SecondaryActivity . In that case, I'd suggest calling SecondaryActivity with startActivityForResult . Then in your onPostExecute , call setResult to set a flag or some data.

Finally, in MainActivity override onActivityResult to call doSomething when the request code corresponds to SecondaryActivity .

Answer 3

So your requirement is to have a single instance of MainActivity. Data in MainActivity may be updated from within MainActivity or from SecondaryActivity. In either case the data to be updated is obtained using an AsyncTask.

My Suggestion

Add the following to the MainActivity in manifest, (More about android:launchMode here.)

android:launchMode="singleInstance"

When you are done interacting with SecondaryActivity, do this,

Intent intent = new Intent(this, MainActivity.class);
    intent.putExtra("DATA1", "your_data1");
    intent.putExtra("DATA2", "your_data2");
    startActivity(intent);
    finish();

Then in your MainActivity,

@Override
protected void onNewIntent(Intent intent) {
    super.onNewIntent(intent);

    String data1 = intent.getStringExtra("DATA1");
    String data2 = intent.getStringExtra("DATA2");
}

Then call AsyncTask in MainActivity using data1 and data2.

NOTE: This is one way to approach your problem. There are other approaches such as startActivityForResult() depending on your requirement.

UPDATE If you want to cancel your AsyncTask, call asyncTask.cancel(true); However, this will not ensure your HttpRequest is aborted, as the cancel will take effect after the request has completed. The work-around for this is a bit hackish. After calling cancel(), contineously check if isCancelled() is true, then do httpRequest.abort() This will only be the fastest way to finish your async task. Need not necessarily mean the request gets aborted.

Answer 4

Try this in your UpsertTask class.

private Context mContext;

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

@Override
protected void onPostExecute(Object o) {
    super.onPostExecute(o);

    if(mContext instanceof MainActivity){
        ((MainActivity) mContext).doSomething();
    }
    else if(mContext instanceof SecondActivity){
        ((SecondActivity) mContext).doSomethingElse();
    }
}

Answer 5

@Override
protected void onPostExecute(Boolean result){
    super.onPostExecute(result);
    # activity is defined as this.activity
    if (activity != null) {
       if(activity instanceof MainActivity) {
         activity.doSomething();
       } else if(activity instanceof SecondaryActivity) {
         activity.doSomethingElse();
       }
    }
}

I think that would work. (if you understand your question correctly).

Answer 6

One way this could be done is by using an event bus. This is a way of passing messages/data between activities. You can post to the bus and then activities can listen for the message if they register.

EventBus class (seperate)

public class EventBus extends Bus {
    private static final EventBus bus  = new EventBus();   
    public static Bus getInstance() { return bus; }    
    private EventBus() {}
}

MainActivity class

...
@Override
protected void onResume() {
    super.onResume();
    EventBus.getInstance().register(this);
}

@Override
protected void onPause() {
    super.onPause();
    EventBus.getInstance().unregister(this);
}

@Subscribe
public void asyncDone(String message) {
    foo(message)       
}

AsyncTask class

...
@Override
protected void onPostExecute(Boolean result){
    super.onPostExecute(result);
    EventBus.getInstance().post("My data")

Thanks to @theheartbreakpug from Reddit for giving me this solution.