CODEWITHSUNDEEP
androidandroid-asynctask
Andrew Matthews
Andrew Matthews

Reputation: 3

What is the purpose of adding parameters to an AsyncTask?

Sorry for being a newbie, I've looked everywhere and I just don't get it.

Asynctask needs 3 parameters; e.g.

but what is the point of these parameters?

I am trying to run a geocoder in a separate thread and I have this

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

but I literally made those parameters up. I have no idea what I'm supposed to put there. I don't need a progress bar or anything to be transferred to the other thread except for the line of code that is already in doInBackground() . Then I need a string to be returned from that, and I am using onPostExecute(String returnedAddress) for that.

I am confused. Help please!

Upvotes: 0

Views: 200

Answers (3)

user1676075
user1676075

Reputation: 3086

Rather than an API reference, here's a little more description. First, many people will use an AsyncTask inline as an anonymous class; keep that in mind. It looks like you've extended it with your own class (which is totally fine), but it likely means you're passing the necessary data in the constructor and referencing it as class variables. In that case, some of the arguments won't make as much sense.

So picture an anonymous inline class of AsyncTask. The first thing it's going to do is run some processing in the background. To do that, you need a way to pass data to the doInBackground method (because you don't have a constructor to call and pass it data). So the first argument is the type of data you're going to pass to it. If you don't have to pass anything, use Void, or use Object, or anything at all, really, because it has to be part of the method signature but you'd ignore it anyway.

For many situations, one will want to provide progress updates. For example, you might use the Float type to represent percent complete, or Long to represent bytes read from a file, or String for general messages to a user. You use the progress type to pass out interim progress information (think of uploading a file to facebook or downloading a file, where it updates the notification status with the progress - this is where/how you'd do that). You've said you don't care about it in your case, so use Void and don't bother implementing any progress methods.

Finally, when the task completes, you need to get to the result in the onPostExecute. So your doInBackground will return a value (of this type) and the AsyncTask framework will pass it to onPostExecute. Again, this makes more sense for an anonymous class with no further body. If you'd hold any results in a class member, that's fine also (but unnecessary). If you don't need to do anything on complete, or don't need to pass any data, use Void (and return null from doInBackground). I find it's useful at the least to return a Boolean for "completed successfully or failed," so you have that information (which might influence whether you post a success or failure notification, as notification of task complete is a common onPostExecute operation).

Hope some more explanation with examples helps.

Upvotes: 0

maclir
maclir

Reputation: 3309

Those are for when you want to pass something to it at time of execution or passing between runInBackground and onPostExecute. You can simply make all three Void in class declaration.

AsyncTask | Android Developers

The three types used by an asynchronous task are the following:

  1. Params, the type of the parameters sent to the task upon execution.
  2. Progress, the type of the progress units published during the background computation.
  3. Result, the type of the result of the background computation.

Not all types are always used by an asynchronous task. To mark a type as unused, simply use the type Void:

    private class MyTask extends AsyncTask<Void, Void, Void> { ... }

Upvotes: 0

stinepike
stinepike

Reputation: 54682

From the doc of AsyncTask

The three types used by an asynchronous task are the following:

  • Params, the type of the parameters sent to the task upon execution.
  • Progress, the type of the progress units published during the background computation.
  • Result, the type of the result of the background computation

Not all types are always used by an asynchronous task. To mark a type as unused, simply use the type Void:

 private class MyTask extends AsyncTask<Void, Void, Void> { ... }

Upvotes: 2

Related Questions