How to refer to a result of AsyncTask in another class?

Question

I have 2 classes: FeedItem and imgDownloader. In the second one I'm scraping url to an image and in the first one I'm making a method setLink, to assign it and display via Picasso in my app.

Fragment of feedItem.class:

public class feedItem {
    String link;

public void setLink(String link) {

    imgDownload task = new imgDownload();
    String urlx = task...;  //Here should be a result of that AsyncTask's doInBackground
    this.link = urlx;
}
}

imgDownload.class:

public class imgDownload extends AsyncTask<String, String, String> {

    feedItem item = new feedItem();
    String url = item.getLink();
    String imglink;

    @Override
    protected String doInBackground(String... params) {
        Document doc = null;
        try {
            doc = Jsoup.connect(url).get();
        }
        catch (IOException e) {
            e.printStackTrace();
        }
        Element masthead = doc.select("div.post-image").select("img[src~=(?i)\\.(png|jpe?g)]").first();
        url = masthead.absUrl("src");
        return url;
    }
    @Override
    protected void onPostExecute(String result) {
        imglink = result; //Result of doInBackground
    }
}

I read almost all similar question to this, but after 2 days od studying I still don't know how to do it properly so I need a concrete answer how to make it.

//////////EDIT

So I used that Callbacks, and I get various errors, like that:

                                                                 --------- beginning of crash
06-27 23:57:14.446 3274-3321/pl.dariusz.app E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #2
                                                            Process: pl.dariusz.app, PID: 3274
                                                            java.lang.RuntimeException: An error occurred while executing doInBackground()
                                                                at android.os.AsyncTask$3.done(AsyncTask.java:309)
                                                                at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354)
                                                                at java.util.concurrent.FutureTask.setException(FutureTask.java:223)
                                                                at java.util.concurrent.FutureTask.run(FutureTask.java:242)
                                                                at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234)
                                                                at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113)
                                                                at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588)
                                                                at java.lang.Thread.run(Thread.java:818)
                                                             Caused by: java.lang.IllegalArgumentException: Must supply a valid URL
                                                                at org.jsoup.helper.Validate.notEmpty(Validate.java:102)
                                                                at org.jsoup.helper.HttpConnection.url(HttpConnection.java:72)
                                                                at org.jsoup.helper.HttpConnection.connect(HttpConnection.java:36)
                                                                at org.jsoup.Jsoup.connect(Jsoup.java:73)
                                                                at pl.dariusz.app.imgDownloader.doInBackground(imgDownloader.java:30)
                                                                at pl.dariusz.app.imgDownloader.doInBackground(imgDownloader.java:12)
                                                                at android.os.AsyncTask$2.call(AsyncTask.java:295)
                                                                at java.util.concurrent.FutureTask.run(FutureTask.java:237)
                                                                at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 
                                                                at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 
                                                                at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 
                                                                at java.lang.Thread.run(Thread.java:818)

06-27 23:57:14.533 3274-3302/pl.dariusz.app I/Process: Sending signal. PID: 3274 SIG: 9

you can implement an interface and set it in constructor of task — adnbsr, Jun 27 '16 at 20:19

score 0 · Answer 1 · answered Jun 27 '16 at 20:16

You need to create a callback which your AsyncTask can use to send data to its calling Activity.

A simple interface that can take the Strings from the AsyncTask should suffice.

You can find a very simple example of this method passing images in my Learn Android repository.

score 0 · Answer 2 · edited May 23 '17 at 10:28

Add constructor for the Async task with parameter your desired property. Something like that:

public class ImgDownload extends AsyncTask<String, String, String> {

    feedItem item = new feedItem();
    String url = item.getLink();
    String imglink;

    public ImgDownload(String link){
         imglink = link;
    } 

    @Override
    protected String doInBackground(String... params) {
        Document doc = null;
        try {
            doc = Jsoup.connect(params[0]).get();
        }
        catch (IOException e) {
            e.printStackTrace();
        }
        Element masthead = doc.select("div.post-image").select("img[src~=(?i)\\.(png|jpe?g)]").first();
        url = masthead.absUrl("src");
        return url;
    }
    @Override
    protected void onPostExecute(String result) {
        imglink = result; //Result of doInBackground
    }
}

and call this async task like:

public class feedItem {
    String mLink;

    public void setLink(String rawLink) {
        imgDownload task = new imgDownload(mLink);
        task.execute(rawLink);
    }
}

More: Тhis solutions is ugly. Its works, but its not flexible. You can create an interface that you can use for callback. Take a look here. Its exactly the right way.

I used that method from your link, but it does not work (look edit of my post). — bioreset, Jun 28 '16 at 00:02

score 0 · Answer 3 · answered Jun 27 '16 at 20:35

0

 imgDownload task = new imgDownload();
 String result = task.execute().get; // result is the output from onPostExecute.

answered Jun 27 '16 at 20:35

ugur

3,604
3
26
57

score 0 · Answer 4 · edited May 23 '17 at 12:18

0

I wrote up a complete guide of how to do it here: https://stackoverflow.com/a/36166643/3962091

The general process is to put your AsyncTask in its own class file, and declare a callback interface within the AsyncTask to which you will send results. Then any other class (including an Activity) can simply implement the callback interface to get any results the AsyncTask has to offer.

edited May 23 '17 at 12:18

Community

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1

answered Jun 27 '16 at 20:37

NoChinDeluxe

3,446
1
16
29

How to refer to a result of AsyncTask in another class?

4 Answers4