我正在尝试使用onBackPressed因此用户可以取消asynctask操作。但是当你按下设备上的后退按钮时，它什么都不做。我的asynctask仍然运行，我的进度对话框仍然显示。有人可以帮助我并帮助我找出问题。
public class ListView extends ListActivity {
ArrayList<HashMap<String, String>> questionList;
final String TAG_RESULTS = "results";
final String TAG_QUESTION_SUBJECT = "Subject";
final String TAG_QUESTION_NUMANSWERS = "NumAnswers";
final String TAG_QUESTION = "question";
final String TAG_QUESTION_CONTENT = "Content";
final String TAG_QUESTION_CHOSENANSWER = "ChosenAnswer";
final String TAG_ANSWERS = "Answers";
final String TAG_ANSWER = "Answer";
final String TAG_ANSWERS_CONTENT = "content";
final String TAG_QUERY = "query";
ProgressDialog pDialog;
LoadAllData mTask;
JSONArray question = null;
android.widget.ListView lv;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.listview);
questionList = new ArrayList<HashMap<String, String>>();
mTask = new LoadAllData();
mTask.execute();
}
@Override
protected void onListItemClick(android.widget.ListView l, View v, int pos, long id) {
super.onListItemClick(l, v, pos, id);
HashMap<String, String> item = questionList.get(pos);
Intent i = new Intent(ListView.this, SingleListItem.class);
i.putExtra(TAG_QUESTION_SUBJECT, item.get(TAG_QUESTION_SUBJECT));
i.putExtra(TAG_QUESTION_CONTENT, item.get(TAG_QUESTION_CONTENT));
i.putExtra(TAG_QUESTION_CHOSENANSWER, item.get(TAG_QUESTION_CHOSENANSWER));
startActivity(i);
}
@Override
public void onBackPressed()
{
/** If user Pressed BackButton While Running Asynctask
this will close the ASynctask.
*/
if (mTask != null && mTask.getStatus() != AsyncTask.Status.FINISHED)
{
mTask.cancel(true);
}
super.onBackPressed();
}
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
/** If Activity is Destroyed While Running Asynctask
this will close the ASynctask. */
if (mTask != null && mTask.getStatus() != AsyncTask.Status.FINISHED)
{
mTask.cancel(true);
}
super.onDestroy();
}
@Override
protected void onPause() {
// TODO Auto-generated method stub
if (pDialog != null)
{
if(pDialog.isShowing())
{
pDialog.dismiss();
}
super.onPause();
}
}
class LoadAllData extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(ListView.this);
pDialog.setMessage("Loading Data. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
try {
Intent in = getIntent();
String searchTerm = in.getStringExtra("TAG_SEARCH");
String query = URLEncoder.encode(searchTerm, "utf-8");
String URL = "http://rxample.com";
JSONParsser jParser = new JSONParsser();
JSONObject json = jParser.readJSONFeed(URL);
try {
JSONArray questions = json.getJSONObject("all").getJSONArray("questions");
for(int i = 0; i < questions.length(); i++) {
JSONObject question = questions.getJSONObject(i);
String Subject = question.getString(TAG_QUESTION_SUBJECT);
String ChosenAnswer = question.getString(TAG_QUESTION_CHOSENANSWER);
String Content = question.getString(TAG_QUESTION_CONTENT);
//JSONArray Answers = question.getJSONObject(TAG_ANSWERS).getJSONArray(TAG_ANSWER);
//JSONObject Answer = Answers.getJSONObject(0);
//String Content = Answer.getString(TAG_ANSWERS_CONTENT);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_QUESTION_SUBJECT, Subject);
map.put(TAG_QUESTION_CONTENT, Content);
map.put(TAG_QUESTION_CHOSENANSWER, ChosenAnswer);
questionList.add(map);
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return TAG_QUESTION ;
}
@Override
protected void onPostExecute(String file_URL) {
if (pDialog != null && pDialog.isShowing()) pDialog.dismiss();
ListAdapter adapter = new SimpleAdapter(getBaseContext(), questionList,
R.layout.listelements,
new String[] { TAG_QUESTION_SUBJECT }, new int[] {
R.id.Subject,});
setListAdapter(adapter);
}
}
@Override
protected void onStop() {
// TODO Auto-generated method stub
super.onStop();
}
}
答案 0 :(得分：1)
我认为你的ProgressDialog的工作存在问题。在前面工作时正在捕捉按钮单击。而且你不能因为pDialog.setCancelable(false);
在真实pDialog.setCancelable( true )上更改可取消，并设置OnCancelListener，当对话框被取消时，该{{3}}会被调用。
答案 1 :(得分：0)
取消AsyncTask时，会设置已取消的标记。在doInBackground()功能中，您需要检查isCancelled()以查看是否已调用cancel()。取消任务时也不会调用onPostExecute()。而是实施onCancelled(Object)来清理你需要的任何东西。
class LoadAllData extends AsyncTask<String, String, String> {
@Override
protected void onPreExecute() {
super.onPreExecute();
pDialog = new ProgressDialog(ListView.this);
pDialog.setMessage("Loading Data. Please wait...");
pDialog.setIndeterminate(false);
pDialog.setCancelable(false);
pDialog.show();
}
protected String doInBackground(String... args) {
try {
Intent in = getIntent();
String searchTerm = in.getStringExtra("TAG_SEARCH");
String query = URLEncoder.encode(searchTerm, "utf-8");
String URL = "http://rxample.com";
JSONParsser jParser = new JSONParsser();
JSONObject json = jParser.readJSONFeed(URL);
try {
JSONArray questions = json.getJSONObject("all").getJSONArray("questions");
//Stop looping on cancel
for(int i = 0; i < questions.length()&&!isCancelled(); i++) {
JSONObject question = questions.getJSONObject(i);
String Subject = question.getString(TAG_QUESTION_SUBJECT);
String ChosenAnswer = question.getString(TAG_QUESTION_CHOSENANSWER);
String Content = question.getString(TAG_QUESTION_CONTENT);
//JSONArray Answers = question.getJSONObject(TAG_ANSWERS).getJSONArray(TAG_ANSWER);
//JSONObject Answer = Answers.getJSONObject(0);
//String Content = Answer.getString(TAG_ANSWERS_CONTENT);
HashMap<String, String> map = new HashMap<String, String>();
map.put(TAG_QUESTION_SUBJECT, Subject);
map.put(TAG_QUESTION_CONTENT, Content);
map.put(TAG_QUESTION_CHOSENANSWER, ChosenAnswer);
questionList.add(map);
}
} catch (JSONException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return TAG_QUESTION ;
}
@Override
protected void onPostExecute(String file_URL) {
if (pDialog != null && pDialog.isShowing()) pDialog.dismiss();
ListAdapter adapter = new SimpleAdapter(getBaseContext(), questionList,
R.layout.listelements,
new String[] { TAG_QUESTION_SUBJECT }, new int[] {
R.id.Subject,});
setListAdapter(adapter);
}
@Override
protected void onCancelled(String result) {
//Clean up
if (pDialog != null && pDialog.isShowing()) pDialog.dismiss();
...
}
}
答案 2 :(得分：0)
AsyncTask cancel（）不会终止您的异步任务。它只是设置一个布尔标志，因此任务对象上的isCancelled（）返回true，这样你就可以从长时间运行的doInBackground中拯救出来。我相信一切都按照你上面的代码的预期工作。如果任务被取消onPostExecute将不会运行，因此您的进度对话框不会被解除。它会调用onCancelled（）而不是。