无法执行任务:任务已执行 下载项目时出错

Question

1. 我已经在我的代码中添加了AssyncTask，但是一旦我从服务器下载数据，我就遇到了这个问题......任何人都给我建议。
2. assyncTask 执行多次。它说任务已经执行了。
3. 请为此提供任何解决方案。
4. 在代码下面，我发布了整个代码。

5. 扩展 AssyncTask 的代码出现错误

   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

你需要将你的DownloadManager与AsyncTask分开，创建不同的类来扩展AsyncTask，例如MyDownloaderAsyncTask，这个类将执行实际的后台工作，你的DownloadManager每次都会创建MyDownloaderAsyncTask的新实例并执行它。 您的类应如下所示：

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

根据 AsyncTask 的线程规则部分：

该任务只能执行一次(如果 尝试第二次执行。

您只能执行一次AsyncTask，因此在执行任务时应始终创建一个新：

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

而不是：

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

您可能需要重构DownloadManager类，或创建一个新的AsyncTask子类。