我使用AsyncTask with Progress Dialog从服务器下载数据库。我想为用户提供取消下载任务的选项。
我的目的是在用户点击进度对话框上的Cancel button时解除进度对话框并取消AsyncTask。
我已应用了大量代码示例，但它们仅帮助解除进度对话框，无法停止或取消下载任务。
关于我在下面的代码行， ，您能给一点帮助吗？非常感谢。
已编辑版本
public class Download_gram extends Activity {
// File url to download
private static String url = "https://dl.dropbox.com/u/15034088/Anhroid_Dict/grammar.nvk.zip";
private static DownloadFile newTask;
// Progress Dialog
private ProgressDialog progressDialog;
// Progress dialog type (0 - for Horizontal progress bar)
public static final int progress_bar = 0;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.download_gram);
newTask = new DownloadFile();
startDownload_gram = (Button) findViewById(R.id.btnProgressBar_gram);
//start download event and show progress bar
startDownload_gram.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
//Checi if file exists
File fgram = new File(Environment.getExternalStorageDirectory()+"/my_Folder/db/my_file/my_file.nvk");
if(fgram.exists())
{
Toast.makeText(getApplicationContext(), "File installed.", Toast.LENGTH_LONG).show();
}
else
{
//checking if the user has an internet connection
ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo info = cm.getActiveNetworkInfo();
if (info != null) {
if (!info.isConnected()) {
Toast.makeText(getApplicationContext(), "No Internet connection!", Toast.LENGTH_SHORT).show();
}
// execute async task
else
//new DownloadFile().execute(url);
newTask.execute(url);
}
else {
Toast.makeText(getApplicationContext(), "No Internet connection!", Toast.LENGTH_SHORT).show();
}
}
}});
}
//show progress dialog
@Override
protected Dialog onCreateDialog(int id) {
switch (id) {
case progress_bar:
progressDialog = new ProgressDialog(this);
progressDialog.setMessage("Downloading… Please wait.");
progressDialog.setIndeterminate(false);
progressDialog.setMax(100);
progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
progressDialog.setCancelable(false);
progressDialog.setButton(DialogInterface.BUTTON_NEGATIVE, "Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog, int which) {
dismissDialog(progress_bar);
newTask.cancel(true);
}
});
progressDialog.show();
return progressDialog;
default:
return null;
}
}
//backgroound downloading
class DownloadFile extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
showDialog(progress_bar);
}
@Override
protected String doInBackground(String... args) {
while (url != null) {
int count;
try {
URL url = new URL(args[0]);
URLConnection conection = url.openConnection();
conection.connect();
// getting file length
int fileLength = conection.getContentLength();
InputStream is = new BufferedInputStream(url.openStream(), 8192);
OutputStream os = new FileOutputStream(Environment.getExternalStorageDirectory().getPath() + "/_nvk_gram.zip");
byte data[] = new byte[1024];
long total = 0;
while ((count = is.read(data)) != -1) {
total += count;
publishProgress(""+(int)((total*100)/fileLength));
// writing data to file
os.write(data, 0, count);
}
// flush output
os.flush();
os.close();
is.close();
} catch (Exception e) {
Log.e("Error: ", e.getMessage());
}
//Unzip the downloaded zip file
{
String destinationDirectory = Environment.getExternalStorageDirectory().getPath() + "/my_Folder/db/my_file/";
int BUFFER = 2048;
List<String> zipFiles = new ArrayList<String>();
File sourceZipFile = new File(Environment.getExternalStorageDirectory().getPath() + "/_nvk_gram.zip");
File unzipDestinationDirectory = new File(destinationDirectory);
unzipDestinationDirectory.mkdir();
ZipFile zipFile = null;
// Open Zip file for reading
try {
zipFile = new ZipFile(sourceZipFile, ZipFile.OPEN_READ);
} catch (IOException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
// Create an enumeration of the entries in the zip file
Enumeration<? extends ZipEntry> zipFileEntries = zipFile.entries();
// Process each entry
while (zipFileEntries.hasMoreElements()) {
// grab a zip file entry
ZipEntry entry = (ZipEntry) zipFileEntries.nextElement();
String currentEntry = entry.getName();
File destFile = new File(unzipDestinationDirectory, currentEntry);
//destFile = new File(unzipDestinationDirectory, destFile.getName());
if (currentEntry.endsWith(".zip")) {
zipFiles.add(destFile.getAbsolutePath());
}
// grab file's parent directory structure
File destinationParent = destFile.getParentFile();
// create the parent directory structure if needed
destinationParent.mkdirs();
try {
// extract file if not a directory
if (!entry.isDirectory()) {
BufferedInputStream is =
new BufferedInputStream(zipFile.getInputStream(entry));
int currentByte;
// establish buffer for writing file
byte data[] = new byte[BUFFER];
// write the current file to disk
FileOutputStream fos = new FileOutputStream(destFile);
BufferedOutputStream dest =
new BufferedOutputStream(fos, BUFFER);
// read and write until last byte is encountered
while ((currentByte = is.read(data, 0, BUFFER)) != -1) {
dest.write(data, 0, currentByte);
}
dest.flush();
dest.close();
is.close();
}
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
try {
zipFile.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
for (Iterator<String> iter = zipFiles.iterator(); iter.hasNext();) {
String zipName = (String)iter.next();
doUnzip(
zipName,
destinationDirectory +
File.separatorChar +
zipName.substring(0,zipName.lastIndexOf(".zip"))
);
if(isCancelled())return (null);
}
}
}
File fav_ifo = new File(Environment.getExternalStorageDirectory()+"/my_Folder/db/my_file/my_file.nvk");
if(fav_ifo.exists())
{
try {
AssetManager am = getAssets();
String fileName = "my_file.ifo";
File destinationFile = new File(Environment.getExternalStorageDirectory()+"/my_Folder/db/my_file/" + fileName);
InputStream in = am.open("my_file.ifo");
FileOutputStream f = new FileOutputStream(destinationFile);
byte[] buffer = new byte[1024];
int len1 = 0;
while ((len1 = in.read(buffer)) > 0) {
f.write(buffer, 0, len1);
}
f.close();
} catch (Exception e) {
Log.d("CopyFileFromAssetsToSD", e.getMessage());
}
}
else
{
}
//Delete the downloaded zip
File folder = Environment.getExternalStorageDirectory();
String fileName = folder.getPath() + "/_nvk_gram.zip";
File myFile = new File(fileName);
if(myFile.exists())
myFile.delete();
return null;
}
private void doUnzip(String zipName, String string) {
// TODO Auto-generated method stub
}
//updating progress bar
protected void onProgressUpdate(String... progress) {
//progress percentage
progressDialog.setProgress(Integer.parseInt(progress[0]));
}
@Override
protected void onPostExecute(String file_url) {
dismissDialog(progress_bar);
//toast to notify user of download completion
Toast.makeText(getApplicationContext(), "Database successfully downloaded.", Toast.LENGTH_LONG).show();
Intent mainIntent = new Intent(Download_gram.this, my_Main_class.class);
Download_gram.this.startActivity(mainIntent);
}
}
}
答案 0 :(得分：1)
看你应该跟踪你的DownloadFile（aSyncTask）类对象。
在
中创建一个新变量public class Download_gram extends Activity {
// File url to download
private static String url = "http://www.abc.123.zip";
private static DownloadFile newTask; // ADDED BY ME
// ... ...
调用
时应保存对象引用new DownloadFile().execute("Url String"); //you must be doing this
//instead you should do
newTask = new DownloadFile();
newTask.execute("Url String"); // YOUR OBJECT IS IN newTask
...
// keep track of this newTask variable
// when ever you want to cancel just call
newTask.cancel(true); // ADDED BY ME
dialog.dismiss();//In fact, I want to apply the code to stop both Progress Dialog and AsynTask here.
设置newTask取消后，你应该在doInBackground中及时检查你的任务被取消了吗？如果是，则退出doInBackground
// YOU CAN USE THIS IN WHILE LOOP OF doInBakcground
if(isCancelled())return (null);
//This will exit doInBackground function and hence cancel task.
// you can perform other operations too in this "if" statement as per your need.
供参考这些功能
http://developer.android.com/reference/android/os/AsyncTask.html#cancel(boolean）
＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃ 新版本 ＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃＃。您尚未检查任务是否已取消。如果iscancelled为true，则必须检查asynctask中发生的下载正在进行中返回（null）;停止asynctask并停止下载。 你应该替换以下代码：
while ((count = is.read(data)) != -1) { // inside doInBackground
total += count;
publishProgress(""+(int)((total*100)/fileLength));
// writing data to file
os.write(data, 0, count);
if(isCancelled())return (null); // ADDED BY ME
}
上面添加的行必须检查任务是否被取消，这个doInBackground函数应该结束。
答案 1 :(得分：0)
你可以这样做，
progressDialog.setOnCancelListener(new DialogInterface.OnCancelListener(){
public void onCancel(DialogInterface dialog) {
yourAysncTask.cancel(true);
}
});
答案 2 :(得分：0)
你应该
yourAsyncTask.cancel(true);
并且，在你的类DownloadFile中，你应该检查 isCanceled（）并在if为真时返回。