我正在使用像这样的AsyncTask：
public class DownloadTask extends AsyncTask<String, Integer, String> {
ProgressDialog mProgressDialog;
private Context context;
private PowerManager.WakeLock mWakeLock;
String fileName=null;
public DownloadTask(Context context,ProgressDialog Dialog) {
this.context = context;
this.mProgressDialog=Dialog;
}
@Override
protected String doInBackground(String... sUrl) {
InputStream input = null;
OutputStream output = null;
HttpURLConnection connection = null;
try {
URL url = new URL(sUrl[0]);
connection = (HttpURLConnection) url.openConnection();
connection.connect();
if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
return "Server returned HTTP " + connection.getResponseCode()
+ " " + connection.getResponseMessage();
}
String raw = connection.getHeaderField("Content-Disposition");
if(raw != null && raw.indexOf("=") != -1) {
fileName = raw.split("=")[1];
fileName=fileName.split(";")[0];
fileName=fileName.substring(1, fileName.length()-1);
} else {
}
File f=new File(context.getFilesDir()+"/"+fileName);
if(!f.exists())
{Log.d("TAG","DOES NOT EXIST , downloading");
int fileLength = connection.getContentLength();
input = connection.getInputStream();
Log.d("Tag", raw);
Log.d("Tag",fileName);
output = new FileOutputStream(context.getFilesDir()+"/"+fileName);
byte data[] = new byte[4096];
long total = 0;
int count;
while ((count = input.read(data)) != -1) {
if (isCancelled()) {
input.close();
File check =new File(context.getFilesDir()+"/"+fileName);
check.delete();
return null;
}
total += count;
if (fileLength > 0)
publishProgress((int) (total * 100 / fileLength));
output.write(data, 0, count);
}
} }catch (Exception e) {
return e.toString();
} finally {
try {
if (output != null)
output.close();
if (input != null)
input.close();
} catch (IOException ignored) {
}
if (connection != null)
connection.disconnect();
}
return null;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
getClass().getName());
mWakeLock.acquire();
mProgressDialog.show();
}
@Override
protected void onProgressUpdate(Integer... progress) {
super.onProgressUpdate(progress);
mProgressDialog.setIndeterminate(false);
mProgressDialog.setMax(100);
mProgressDialog.setProgress(progress[0]);
}
@Override
protected void onPostExecute(String result) {
mWakeLock.release();
mProgressDialog.dismiss();
if (result != null)
Toast.makeText(context,"Download error: "+"Please check your internet connection!", Toast.LENGTH_LONG).show();
else
{ Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show();
Intent i=new Intent(context,MuPDFActivity.class);
Uri uri=Uri.parse(context.getFilesDir()+"/"+fileName);
i.setAction(Intent.ACTION_VIEW);
i.setData(uri);
context.startActivity(i);
}
}}
当我从我的活动中调用它并且下载文件时，这有效。但是，如果下载中断（如果用户打开打开的应用程序列表并强制退出），则部分下载的文件仍然存在，并且已经损坏。 我不想恢复下载，如果下载中断，我想删除该文件。我怎么做？
答案 0 :(得分：1)
如果用户甚至按下主页按钮或旋转设备，则下载中断。因此，在onStop（）方法中，您必须检查不在onPostExecute（String result）中的文件，因为它可能不会调用，可能会继续下载。您只需检查文件末尾是否有EOF，而不需要SharedPreferences。
答案 1 :(得分：0)
jitain sharma关于取消asynctask的解决方案的想法不起作用（当强制退出应用程序时，它没有被调用）。
所以，最后，我使用sharedPreferences在我的AsyncTask的onPostExecute（）方法中“标记”文件下载结束。我只是检查结果，如果一切正常（那么字符串将为null），I我正在添加一个带有值为“DONE”的文件名的SharedPreference。
在执行AsyncTask之前，我正在检查文件是否存在以及是否存在sharedPreference。
public class DownloadTask extends AsyncTask<String, Integer, String> {
ProgressDialog mProgressDialog;
private Context context;
private PowerManager.WakeLock mWakeLock;
String fileName=null;
public DownloadTask(Context context,ProgressDialog Dialog) {
this.context = context;
this.mProgressDialog=Dialog;
}
@Override
protected String doInBackground(String... sUrl) {
InputStream input = null;
OutputStream output = null;
HttpURLConnection connection = null;
try {
URL url = new URL(sUrl[0]);
connection = (HttpURLConnection) url.openConnection();
connection.setReadTimeout(3000);
connection.setConnectTimeout(5000);
connection.connect();
if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
return "Server returned HTTP " + connection.getResponseCode()
+ " " + connection.getResponseMessage();
}
String raw = connection.getHeaderField("Content-Disposition");
if(raw != null && raw.indexOf("=") != -1) {
fileName = raw.split("=")[1];
fileName=fileName.split(";")[0];
fileName=fileName.substring(1, fileName.length()-1);
} else {
}
File f=new File(context.getFilesDir()+"/"+fileName);
if(!f.exists())
{Log.d("TAG","DOES NOT EXIST , downloading");
int fileLength = connection.getContentLength();
input = connection.getInputStream();
Log.d("Tag", raw);
Log.d("Tag",fileName);
output = new FileOutputStream(context.getFilesDir()+"/"+fileName);
byte data[] = new byte[4096];
long total = 0;
int count;
while ((count = input.read(data)) != -1) {
if (isCancelled()) {
input.close();
File check =new File(context.getFilesDir()+"/"+fileName);
check.delete();
return null;
}
total += count;
if (fileLength > 0)
publishProgress((int) (total * 100 / fileLength));
output.write(data, 0, count);
}
} }catch (Exception e) {
return e.toString();
} finally {
try {
if (output != null)
output.close();
if (input != null)
input.close();
} catch (IOException ignored) {
}
if (connection != null)
connection.disconnect();
}
return null;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
PowerManager pm = (PowerManager) context.getSystemService(Context.POWER_SERVICE);
mWakeLock = pm.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK,
getClass().getName());
mWakeLock.acquire();
mProgressDialog.show();
}
@Override
protected void onProgressUpdate(Integer... progress) {
super.onProgressUpdate(progress);
mProgressDialog.setIndeterminate(false);
mProgressDialog.setMax(100);
mProgressDialog.setProgress(progress[0]);
}
@Override
protected void onPostExecute(String result) {
mWakeLock.release();
mProgressDialog.dismiss();
if (result != null)
{File file=new File(context.getFilesDir()+File.separator+fileName);
file.delete();
Toast.makeText(context,"Download error: "+"Please check your internet connection!", Toast.LENGTH_LONG).show();
}
//**THIS IS THE CHANGE** else
{ SharedPreferences p=PreferenceManager.getDefaultSharedPreferences(context);
Editor editor=p.edit();
editor.putString(fileName, "DONE");
editor.commit();
Toast.makeText(context,"File downloaded", Toast.LENGTH_SHORT).show();
Intent i=new Intent(context,MuPDFActivity.class);
Uri uri=Uri.parse(context.getFilesDir()+"/"+fileName);
i.setAction(Intent.ACTION_VIEW);
i.setData(uri);
context.startActivity(i);
}
}}
以下是我的检查方式：
if(!file.exists()||!PreferenceManager.getDefaultSharedPreferences(getApplicationContext()).contains(fileName))
{ 新文件（getFilesDir（）+ File.separator +“phychap1.pdf”）。delete（）; }
我总是愿意接受更好的解决方案