在 Android 中取消异步任务
Cancelling an Async Task In Android
我正在尝试在一段时间后取消异步任务。我已经搜索并发现了很多关于此的问题，并且所有问题的答案都与我在下面所做的相同。
问题：调用取消后，web 服务似乎没有取消，因为它从未到达 onPostExecute。
请提供任何帮助。
我尝试过的：
一段时间后我打电话给
class TimeOut 将 asyncTask 作为其参数并执行以下操作：
if (task.getStatus() == AsyncTask.Status.RUNNING )
{task.cancel(true);}
if(task.isCancelled()==true)
{
Log.e(TAG,"TASK IS CANCELLED");
}
在我的异步中 class
@Override
protected void onCancelled() {
webServiceError=true; //when timeout change it to true.(default false)
Toast.makeText(context, R.string.webserviceDownloadUserDataError, Toast.LENGTH_LONG).show();
if (pd.isShowing()) {
pd.dismiss();
}
super.onCancelled();
}
@Override
protected String doInBackground(String... params) {
int paramsTracker = 0;
webServiceError = false;
while(webServiceError==false) {
HttpClient httpclient = new DefaultHttpClient();
String url = params[paramsTracker];
paramsTracker = paramsTracker + 1;
HttpPost httppost = new HttpPost(url);
int paramsCount = params.length;
try {
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(paramsCount);
for (int i = 0; i < (paramsCount - 1) / 2; i++) {
Log.d(TAG, "parameters: " + params[paramsTracker] + " - " + params[paramsTracker + 1]);
nameValuePairs.add(new BasicNameValuePair(params[paramsTracker], params[paramsTracker + 1]));
paramsTracker = paramsTracker + 2;
}
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
// execute http post request, call web service
response = httpclient.execute(httppost);
}
catch (Exception e) {
webServiceError = true;
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error in calling web service " + e.toString(), LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
if (webServiceError == false) {
int CNT = 0;
try {
String query = "SELECT COUNT(*) AS CNT FROM TASKS";
Cursor cursor = MainActivity.myDataBase.rawQuery(query, null);
if (cursor.moveToFirst()) {
do {
CNT = Integer.parseInt(cursor.getString(cursor.getColumnIndex("CNT")));
} while (cursor.moveToNext());
cursor.close();
}
} catch (Exception e) {
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error in Database error getting task count " + e.toString(), LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
if (CNT == 0) {
String webServiceResponse = "";
try {
Log.d(TAG, "Getting web service response");
// get web service response
HttpEntity entity = response.getEntity();
String content;
content = EntityUtils.toString(entity);
// Log.d(TAG, "content: "+ content);
// parse XML response
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
InputSource is = new InputSource();
is.setCharacterStream(new StringReader(content));
Document doc = db.parse(is);
NodeList nodes = doc.getElementsByTagName("string");
Element line = (Element) nodes.item(0);
webServiceResponse = getCharacterDataFromElement(line);
String patternForON = "SET IDENTITY_INSERT \[.*?\] O?((N)|(FF))\s*?;";
Pattern rForON = Pattern.compile(patternForON);
Matcher mForON = rForON.matcher(webServiceResponse);
String webServiceResponseWithOutIdentityInsert = mForON.replaceAll("");
String patternForInsert = "\bINSERT (?!INTO)";
Pattern rForInsert = Pattern.compile(patternForInsert);
Matcher mForInsert = rForInsert.matcher(webServiceResponseWithOutIdentityInsert);
String webServiceResponseWITHOUTINSERTALONE = mForInsert.replaceAll("INSERT INTO ");
String webServiceResponsePURIFIED = webServiceResponseWITHOUTINSERTALONE.replaceAll(";;", ";");
Log.d(TAG, "content: " + webServiceResponsePURIFIED);
///////////END OF for removing queries that are not applicable in SQLITE
//FOR SPLITTING THE QUERIES AND PLACING EACH AT AN INDEX IN contentArray ARRAY
//String contentArray [] = webServiceResponse.split(";");
String contentArray[] = webServiceResponsePURIFIED.split(";");
Log.d(TAG, "contentArray length" + contentArray.length + ""); //GETS THE NUMBER OF QUERIES
pd.setMax(contentArray.length); //SETTING THE PROGRESS DIALOG (MAX PROGRESS)
for (int i = 0; i < contentArray.length; i++) {
// add the downloaded data to the local database
String query = contentArray[i];
try {
AppLogging(TAG, "Queries Downloaded splitted and purified\n query " + i + " :" + contentArray[i], LogFileName.LogFilename);
} catch (Exception l) {
}
Log.d(TAG, "query: " + query);
// if query contains "getdate()" replace with DATETIME('now'), to render the query executable in sqlite
query = query.replace("GETDATE()", "DATETIME('now')");
try {
MainActivity.myDataBase.execSQL(query); //EXECUTE QUERY
} catch (Exception e) {
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error in performing query: " + query + "\nError: " + e, LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
//Log.d("Initialize database, HTTPRequestGetUserData ", query);
publishProgress();
}
} catch (Exception e) {
webServiceError = true;
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error: " + e.toString(), LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
}
}
if (isCancelled()) return "0";
}
return "1";
}
根据 Android AsyncTask 文档，在 AsyncTask 上调用 cancel() 后，它不会调用 onPostExecute()，而是调用 onCancelled()。所以想要流量
现在根据此处的文档，您的代码
@Override
protected String doInBackground(String... params) {
while(webServiceError=false) {
.....//calling webservice
if (isCancelled()) return "0";
}
return "1";
}
现在你的 onCancelled() 看起来像，带有字符串参数
@Override
protected void onCancelled(String object) { // Here object should be 0
webServiceError=true; //when timeout change it to true.(default false)
Toast.makeText(context, R.string.webserviceDownloadUserDataError, Toast.LENGTH_LONG).show();
if (pd.isShowing()) {
pd.dismiss();
}
super.onCancelled();
}
现在在此方法参数中 object will be 0。不用担心 onPostExecute() 和 onCancelled() 这两种方法都会 运行 在主 UI 线程上。
现在我建议您创建一个私有方法，您希望使用字符串参数从 onPostExecute() 和 onCancelled() 执行该方法。
当您取消 AsyncTask 时，它永远不会触发 OnPostExecute 过程。 API 文档中提到了它：
http://developer.android.com/reference/android/os/AsyncTask.html
A task can be cancelled at any time by invoking cancel(boolean). Invoking this method will cause subsequent calls to isCancelled() to return true. After invoking this method, onCancelled(Object), instead of onPostExecute(Object) will be invoked after doInBackground(Object[]) returns. To ensure that a task is cancelled as quickly as possible, you should always check the return value of isCancelled() periodically from doInBackground(Object[]), if possible (inside a loop for instance.)
我正在尝试在一段时间后取消异步任务。我已经搜索并发现了很多关于此的问题，并且所有问题的答案都与我在下面所做的相同。
问题：调用取消后，web 服务似乎没有取消，因为它从未到达 onPostExecute。 请提供任何帮助。
我尝试过的：
一段时间后我打电话给
class TimeOut 将 asyncTask 作为其参数并执行以下操作：
if (task.getStatus() == AsyncTask.Status.RUNNING )
{task.cancel(true);}
if(task.isCancelled()==true)
{
Log.e(TAG,"TASK IS CANCELLED");
}
在我的异步中 class
@Override
protected void onCancelled() {
webServiceError=true; //when timeout change it to true.(default false)
Toast.makeText(context, R.string.webserviceDownloadUserDataError, Toast.LENGTH_LONG).show();
if (pd.isShowing()) {
pd.dismiss();
}
super.onCancelled();
}
@Override
protected String doInBackground(String... params) {
int paramsTracker = 0;
webServiceError = false;
while(webServiceError==false) {
HttpClient httpclient = new DefaultHttpClient();
String url = params[paramsTracker];
paramsTracker = paramsTracker + 1;
HttpPost httppost = new HttpPost(url);
int paramsCount = params.length;
try {
List<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>(paramsCount);
for (int i = 0; i < (paramsCount - 1) / 2; i++) {
Log.d(TAG, "parameters: " + params[paramsTracker] + " - " + params[paramsTracker + 1]);
nameValuePairs.add(new BasicNameValuePair(params[paramsTracker], params[paramsTracker + 1]));
paramsTracker = paramsTracker + 2;
}
httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
// execute http post request, call web service
response = httpclient.execute(httppost);
}
catch (Exception e) {
webServiceError = true;
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error in calling web service " + e.toString(), LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
if (webServiceError == false) {
int CNT = 0;
try {
String query = "SELECT COUNT(*) AS CNT FROM TASKS";
Cursor cursor = MainActivity.myDataBase.rawQuery(query, null);
if (cursor.moveToFirst()) {
do {
CNT = Integer.parseInt(cursor.getString(cursor.getColumnIndex("CNT")));
} while (cursor.moveToNext());
cursor.close();
}
} catch (Exception e) {
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error in Database error getting task count " + e.toString(), LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
if (CNT == 0) {
String webServiceResponse = "";
try {
Log.d(TAG, "Getting web service response");
// get web service response
HttpEntity entity = response.getEntity();
String content;
content = EntityUtils.toString(entity);
// Log.d(TAG, "content: "+ content);
// parse XML response
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
InputSource is = new InputSource();
is.setCharacterStream(new StringReader(content));
Document doc = db.parse(is);
NodeList nodes = doc.getElementsByTagName("string");
Element line = (Element) nodes.item(0);
webServiceResponse = getCharacterDataFromElement(line);
String patternForON = "SET IDENTITY_INSERT \[.*?\] O?((N)|(FF))\s*?;";
Pattern rForON = Pattern.compile(patternForON);
Matcher mForON = rForON.matcher(webServiceResponse);
String webServiceResponseWithOutIdentityInsert = mForON.replaceAll("");
String patternForInsert = "\bINSERT (?!INTO)";
Pattern rForInsert = Pattern.compile(patternForInsert);
Matcher mForInsert = rForInsert.matcher(webServiceResponseWithOutIdentityInsert);
String webServiceResponseWITHOUTINSERTALONE = mForInsert.replaceAll("INSERT INTO ");
String webServiceResponsePURIFIED = webServiceResponseWITHOUTINSERTALONE.replaceAll(";;", ";");
Log.d(TAG, "content: " + webServiceResponsePURIFIED);
///////////END OF for removing queries that are not applicable in SQLITE
//FOR SPLITTING THE QUERIES AND PLACING EACH AT AN INDEX IN contentArray ARRAY
//String contentArray [] = webServiceResponse.split(";");
String contentArray[] = webServiceResponsePURIFIED.split(";");
Log.d(TAG, "contentArray length" + contentArray.length + ""); //GETS THE NUMBER OF QUERIES
pd.setMax(contentArray.length); //SETTING THE PROGRESS DIALOG (MAX PROGRESS)
for (int i = 0; i < contentArray.length; i++) {
// add the downloaded data to the local database
String query = contentArray[i];
try {
AppLogging(TAG, "Queries Downloaded splitted and purified\n query " + i + " :" + contentArray[i], LogFileName.LogFilename);
} catch (Exception l) {
}
Log.d(TAG, "query: " + query);
// if query contains "getdate()" replace with DATETIME('now'), to render the query executable in sqlite
query = query.replace("GETDATE()", "DATETIME('now')");
try {
MainActivity.myDataBase.execSQL(query); //EXECUTE QUERY
} catch (Exception e) {
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error in performing query: " + query + "\nError: " + e, LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
//Log.d("Initialize database, HTTPRequestGetUserData ", query);
publishProgress();
}
} catch (Exception e) {
webServiceError = true;
Log.e(TAG, e.toString());
try {
AppLogging(TAG, "Error: " + e.toString(), LogFileName.ErrorLogFilename);
} catch (Exception a) {
}
}
}
}
if (isCancelled()) return "0";
}
return "1";
}
根据 Android AsyncTask 文档，在 AsyncTask 上调用 cancel() 后，它不会调用 onPostExecute()，而是调用 onCancelled()。所以想要流量
现在根据此处的文档，您的代码
@Override
protected String doInBackground(String... params) {
while(webServiceError=false) {
.....//calling webservice
if (isCancelled()) return "0";
}
return "1";
}
现在你的 onCancelled() 看起来像，带有字符串参数
@Override
protected void onCancelled(String object) { // Here object should be 0
webServiceError=true; //when timeout change it to true.(default false)
Toast.makeText(context, R.string.webserviceDownloadUserDataError, Toast.LENGTH_LONG).show();
if (pd.isShowing()) {
pd.dismiss();
}
super.onCancelled();
}
现在在此方法参数中 object will be 0。不用担心 onPostExecute() 和 onCancelled() 这两种方法都会 运行 在主 UI 线程上。
现在我建议您创建一个私有方法，您希望使用字符串参数从 onPostExecute() 和 onCancelled() 执行该方法。
当您取消 AsyncTask 时，它永远不会触发 OnPostExecute 过程。 API 文档中提到了它：
http://developer.android.com/reference/android/os/AsyncTask.html
A task can be cancelled at any time by invoking cancel(boolean). Invoking this method will cause subsequent calls to isCancelled() to return true. After invoking this method, onCancelled(Object), instead of onPostExecute(Object) will be invoked after doInBackground(Object[]) returns. To ensure that a task is cancelled as quickly as possible, you should always check the return value of isCancelled() periodically from doInBackground(Object[]), if possible (inside a loop for instance.)