How to implement "downloader files" in a method?

Question

I have created a code to download multiple files showing a progressbar progress. This works perfectly, but now I want to deploy it to an external project (library itself) and I have problems.

My intention is to call "download" and when the download completes or returns 0 or 1. But being asynchronous the method returns the value before finishing., I tried to control it without success with "CountdownLatch" ... Any idea?

The following code works, the problem is that the method "download" returns the value without waiting for it to finish the rest of code.

Main.java

if(MyLib.download(Main.this, url, nameFiles, "internal", "folderExtra") == 1){
            System.out.println("SUCCESS DOWNLOAD!");
}else{
            System.out.println("error download");
}

MyLib.java

/** DOWNLOADER WITH PROCESSDIALOG **/
    ProgressDialog pDialog;
    Context context;
    String urlName; 
    String[] filesToDownload;
    int downloadOK = -1;
    int currentFile = -1;
    int totalFiles = 0;
    String typeStorage = "internal";
    String folder = "";
    CountDownLatch controlLatch;
    public int download(Context ctx, String urlName, String[] filesToDownload, String typeStorage, String extraFolder ){

            System.out.println("estoy en download");
            this.context = ctx;
            this.urlName = urlName;
            this.filesToDownload = filesToDownload;
            this.totalFiles = filesToDownload.length;
            this.typeStorage = typeStorage;

            /** Almacenamiento de la descarga - Interno o externo **/
            if (typeStorage.equalsIgnoreCase("internal")) {
                System.out.println("internal");
                this.folder = context.getFilesDir().toString() + "/";
            } else if (typeStorage.equalsIgnoreCase("external")) {
                System.out.println("external");
            }

            /** COMPLETEMENTO DIRECTORIO/S OPCIONAL **/
            if (extraFolder != null && extraFolder != "") {
                folder += extraFolder;
            }

            System.out.println("FOLDER: " + folder);
            File directoryFile = new File(folder);
            if (!directoryFile.isDirectory()) {
                if (!directoryFile.mkdir()) {
                    Toast.makeText(context, "No se puede crear el directorio o no existe", Toast.LENGTH_LONG).show();
                }
            }
            pDialog = new ProgressDialog(context);
            pDialog.setIndeterminate(false);
            pDialog.setCancelable(false);
            pDialog.setMax(100);
            pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            pDialog.setTitle("Descargando recursos...");

            // controlLatch = new CountDownLatch(1);

            startDownload();
            /* 
            try {
                System.out.println("STOP");
                controlLatch.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            */          
        return downloadOK;
    }
private void startDownload() {
    currentFile++;
    System.out.println("startDownload!");
    if (currentFile < totalFiles) {
        pDialog.setMessage("Descargando " + (currentFile + 1) + " de " + totalFiles + "\n\n(..." + filesToDownload[currentFile] + ")");
        System.out.println("startDownload currentFile +[" + currentFile + "] totalFiles [" + totalFiles + "]");
        System.out.println("file: " + filesToDownload[currentFile].toString());
        new DownloaderFile().execute(filesToDownload[currentFile]);
    }
}

private class DownloaderFile extends AsyncTask<String, Integer, String> {

    @Override
    protected String doInBackground(String... params) {
        try {
            File checkFile = new File(folder + params[0]);
            if(!checkFile.exists()){
                URL urlFinal = new URL(urlName+params[0]);
                URLConnection connection = urlFinal.openConnection();
                connection.connect();
                int fileLength = connection.getContentLength();

                InputStream input = new BufferedInputStream(urlFinal.openStream());
                OutputStream output = new FileOutputStream(folder + params[0]);

                byte data[] = new byte[1024];
                long total = 0;
                int count;
                while ((count = input.read(data)) != -1) {
                    total += count;
                    publishProgress((int) (total * 100 / fileLength));
                    output.write(data, 0, count);
                }
                output.flush();
                output.close();
                input.close();
            } else {
                System.out.println("The file " + filesToDownload[currentFile] + " is downloaded"  );
            }
        } catch (Exception e) {
            e.printStackTrace();
            return "error";
        }
        return "ok";

    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();
        System.out.println("-1");
        File checkFile = new File(folder + filesToDownload[currentFile]);
        if(!checkFile.exists()){
            System.out.println("pDialogShow");
            pDialog.show();
        }
    }

    @Override
    protected void onProgressUpdate(Integer... progress) {
        super.onProgressUpdate(progress);
        pDialog.setProgress(progress[0]);
    }

    @Override
    protected void onPostExecute(String res) {
        System.out.println("10");
        if (currentFile == (totalFiles - 1)) {
            System.out.println("FINISH!!!!!!!!!!!!!!");
            currentFile = 0;
            pDialog.dismiss();
            downloadOK = 1;
            //controlLatch.countDown();

        } else {
            if (res.equals("ok")) {
                startDownload();
            } else {
                System.out.println("error download");
                downloadOK = 0;
            }
        }
    }
}

Answer 1

It sounds like you want callback.

Your DownloaderFile class can take a listener interface which is implemented by whatever contains the DownloaderFile object. Call that listener inside onPostExecute().

It might look like this:

public class MyActivity extends Activity implements OnDownloadCompleteListener {
    private void startDownload() {
        //inside whatever method        
        Downloader downloader = new Downloader(this); //'this' implements OnDownloadCompleteListener
        downloader.go();
    }

    @Override 
    public void onDownloadFinished(boolean success) {
        //implementation 

    }
}

Inside Downloader:

//...
@Override
protected void onPostExecute(String res) {
    onDownloadCompleteListener.onDownloadComplete(true);
}

The OnDownloadCompleteListener interface:

public interface OnDownloadCompleteListener {
    public void onDownloadComplete(boolean success);
}