无法执行任务：下载项目时任务已执行错误

Question

1. I have added AssyncTask in my code but once i download data from server i got this issue.. any one give me suggestion.
2. The assyncTask perform multiple times. and it says the task has already been executed.
3. please give any solutions for this.
4. below code i have posted entire code.

5. the code which extends AssyncTask. is getting error

   java.lang.IllegalStateException: Cannot execute task: the task has already been executed (a task can be executed only once) at android.os.AsyncTask.executeOnExecutor(AsyncTask.java:596) at android.os.AsyncTask.execute(AsyncTask.java:551) at com.monnfamily.libraryapp.Utility.DownloadManager.downloadBookData(DownloadManager.java:80) at 

 package com.monnfamily.libraryapp.Utility; import android.content.Context; import android.os.AsyncTask; import android.util.Log; public class DownloadManager extends AsyncTask<String, Void, Boolean> { private static final String TAG = "Download Manager"; public interface DownloadCompletedListner { // you can define any parameter as per your requirement public void downloadCompleted(); } private BookProperties mBookDetails; private DownloadCompletedListner mListner; private static final DownloadManager mInstance = new DownloadManager(); public static DownloadManager getInstance() { return mInstance; } private DownloadManager() { } @Override protected Boolean doInBackground(String... strings) { String tMainFolder = String.valueOf(BaseApplication.getInstance().getAppContext().getDir("MonnFamily", Context.MODE_PRIVATE)); tMainFolder += "/Book" + mBookDetails.getBookId(); downloadBookDetails(tMainFolder, ContentfulConstants.BOOK_MAIN_IMAGE + ".png", mBookDetails.getBookMainImage()); downloadBookDetails(tMainFolder, ContentfulConstants.BOOK_MAIN_AUDIO + ".mp3", mBookDetails.getBookSound()); for (PageDetailProperties pageDetails : mBookDetails.getPageDetail()) { String tPageNumber = pageDetails.getPageNumber().toString(); downloadBookDetails(tMainFolder, ContentfulConstants.PAGE_IMAGE + tPageNumber + ".png", pageDetails.getPageImage()); downloadBookDetails(tMainFolder, ContentfulConstants.PAGE_AUDIO + tPageNumber + ".mp3", pageDetails.getPageAudio()); downloadBookDetails(tMainFolder, ContentfulConstants.PAGE_TEXT + tPageNumber + ".txt", pageDetails.getPageText()); } return true; } protected void onPostExecute(Boolean result) { //This is run on the UI thread so you can do as you wish here if(result){ ((LibraryView)BaseApplication.getInstance().getCurrentActivity()).hideActivityView(); mListner.downloadCompleted(); } } public void downloadBookData(BookProperties pBook){ mBookDetails = pBook; String tMainFolder = String.valueOf(BaseApplication.getInstance().getAppContext().getDir("MonnFamily", Context.MODE_PRIVATE)); tMainFolder += "/Book" + pBook.getBookId(); File directory = new File(tMainFolder); if (!directory.exists()) { directory.mkdir(); ((LibraryView)BaseApplication.getInstance().getCurrentActivity()).showActivityView(); new DownloadManager().execute(); /// error ocuures here } } private void downloadBookDetails(String pMainFolder, String pFileName, String pDownloadURL){ try { URL url = new URL(pDownloadURL); URLConnection ucon = url.openConnection(); ucon.setReadTimeout(5000); ucon.setConnectTimeout(10000); InputStream is = ucon.getInputStream(); BufferedInputStream inStream = new BufferedInputStream(is, 1024 * 5); File directory = new File(pMainFolder, pFileName); FileOutputStream outStream = new FileOutputStream(directory); byte[] buff = new byte[5 * 1024]; int len; while ((len = inStream.read(buff)) != -1) { outStream.write(buff, 0, len); } outStream.flush(); outStream.close(); inStream.close(); } catch (Exception e) { //Add Network Error. Log.e(TAG, "Download Error Exception " + e.getMessage()); e.printStackTrace(); } } public void setListner(DownloadCompletedListner pListner) { this.mListner = pListner; } }

Answer 1

You need to separate your DownloadManager from AsyncTask, Create different class that will extend AsyncTask, for example, MyDownloaderAsyncTask, this class will execute the actual background work, and your DownloadManager will create each time new instance of MyDownloaderAsyncTask and execute it. Your classes should look something like this:

public class MyDownloaderAsyncTask extends AsyncTask<String, Void, Boolean> {

private DownloadManager.DownloadCompletedListner mListner;

private BookProperties mBookDetails;

public MyDownloaderAsyncTask(DownloadManager.DownloadCompletedListner listener, BookProperties bookdetails) {
    mListner=listener;
    mBookDetails=bookdetails;

}

@Override
protected Boolean doInBackground(String... strings) {
    String  tMainFolder = String.valueOf(BaseApplication.getInstance().getAppContext().getDir("MonnFamily", Context.MODE_PRIVATE));
    tMainFolder += "/Book" + mBookDetails.getBookId();
    downloadBookDetails(tMainFolder,  ContentfulConstants.BOOK_MAIN_IMAGE + ".png", mBookDetails.getBookMainImage());
    downloadBookDetails(tMainFolder,  ContentfulConstants.BOOK_MAIN_AUDIO + ".mp3", mBookDetails.getBookSound());

    for (PageDetailProperties pageDetails : mBookDetails.getPageDetail()) {
        String tPageNumber = pageDetails.getPageNumber().toString();
        downloadBookDetails(tMainFolder, ContentfulConstants.PAGE_IMAGE + tPageNumber + ".png", pageDetails.getPageImage());
        downloadBookDetails(tMainFolder,  ContentfulConstants.PAGE_AUDIO + tPageNumber + ".mp3", pageDetails.getPageAudio());
        downloadBookDetails(tMainFolder,  ContentfulConstants.PAGE_TEXT + tPageNumber + ".txt", pageDetails.getPageText());
    }

    return true;
}

protected void onPostExecute(Boolean result) {
    //This is run on the UI thread so you can do as you wish here
    if(result){
        ((LibraryView)BaseApplication.getInstance().getCurrentActivity()).hideActivityView();
        mListner.downloadCompleted();

    }
}

private void downloadBookDetails(String pMainFolder, String pFileName, String pDownloadURL){
    try
    {
        URL url = new URL(pDownloadURL);
        URLConnection ucon = url.openConnection();
        ucon.setReadTimeout(5000);
        ucon.setConnectTimeout(10000);

        InputStream is = ucon.getInputStream();
        BufferedInputStream inStream = new BufferedInputStream(is, 1024 * 5);

        File directory = new File(pMainFolder, pFileName);
        FileOutputStream outStream = new FileOutputStream(directory);
        byte[] buff = new byte[5 * 1024];

        int len;
        while ((len = inStream.read(buff)) != -1)
        {
            outStream.write(buff, 0, len);
        }

        outStream.flush();
        outStream.close();
        inStream.close();
    }
    catch (Exception e)
    {
        //Add Network Error.
        Log.e(TAG, "Download Error Exception " + e.getMessage());
        e.printStackTrace();
    }
}

}

public class DownloadManager {

private static final String TAG = "Download Manager";

public interface DownloadCompletedListner {
    // you can define any parameter as per your requirement
    public void downloadCompleted();
}

private BookProperties mBookDetails;
private DownloadCompletedListner mListner;

private static final DownloadManager mInstance = new DownloadManager();
public static DownloadManager getInstance() {
    return mInstance;
}


private DownloadManager() {
}






public void downloadBookData(BookProperties pBook){
    mBookDetails = pBook;
    String  tMainFolder = String.valueOf(BaseApplication.getInstance().getAppContext().getDir("MonnFamily", Context.MODE_PRIVATE));
    tMainFolder += "/Book" + pBook.getBookId();

    File directory = new File(tMainFolder);
    if (!directory.exists()) {
        directory.mkdir();
        ((LibraryView)BaseApplication.getInstance().getCurrentActivity()).showActivityView();
        new MyDownloaderAsyncTask(mListner, mBookDetails).execute(new String[]);  

    }
}


public void setListner(DownloadCompletedListner pListner) {
    this.mListner = pListner;
}

}

Answer 2

According to the threading rules section of AsyncTask :

The task can be executed only once (an exception will be thrown if a second execution is attempted.)

You can only execute an AsyncTask once, so you should always create a new one whenever you want perform the task:

new DownloadManager().execute(...);

Instead of:

DownloadManager dm = new DownloadManager();
dm.execute(...);
dm.execute(...); // throws IllegalStateException

You may need to refactor your DownloadManager class, or create a new sub-class of AsyncTask .