更改屏幕方向时，我在重新创建 Activity 、进度对话框和异步任务时遇到问题。我在这里看到了一些解决方案，我决定使用 onRetainCustomNonConfigurationInstance() 来保存 AsyncTask 的实例。好吧，在 onCreate 中，我检查是否有 AsyncTask 的实例，如果存在，我会显示一个新的进度对话框。但是这个对话框会在无限循环中阻止 UI(在 onPostExecute 中有dialog.dismiss())，并且 Activity 当然不会显示结果。
创建时
getDirection = (GetDirection) getLastCustomNonConfigurationInstance();
if(getDirection != null) {
dialog = new ProgressDialog(RouteActivity.this);
dialog.setMessage(getResources().getString(R.string.loading_data));
dialog.setIndeterminate(false);
dialog.setCancelable(false);
dialog.show();
} else {
getDirection = new GetDirection();
getDirection.execute();
}
onRetainCustomNonConfigurationInstance
@Override
public Object onRetainCustomNonConfigurationInstance() {
return getDirection;
}
@Override
protected void onDestroy() {
super.onDestroy();
if (dialog.isShowing()) {
dialog.dismiss();
}
}
编辑#1: 我采用了Kingfisher with Fragment and Retained Fragment的解决方案，但是当我在AsyncTask的doInBackground期间改变方向时，Expandable Listview上有一个NPE。
08-14 12:50:40.866: E/AndroidRuntime(22739): FATAL EXCEPTION: main
08-14 12:50:40.866: E/AndroidRuntime(22739): java.lang.NullPointerException
08-14 12:50:40.866: E/AndroidRuntime(22739): at com.pasquini.adapter.ListRouteExpandableAdapter.getGroupCount(ListRouteExpandableAdapter.java:78)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.widget.ExpandableListConnector.getCount(ExpandableListConnector.java:399)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.widget.ListView.setAdapter(ListView.java:460)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.widget.ExpandableListView.setAdapter(ExpandableListView.java:470)
08-14 12:50:40.866: E/AndroidRuntime(22739): at com.pasquini.activity.RouteActivity.onPostExecute(RouteActivity.java:792)
08-14 12:50:40.866: E/AndroidRuntime(22739): at com.pasquini.fragment.GetDirectionFragment$GetDirectionTask.onPostExecute(GetDirectionFragment.java:244)
08-14 12:50:40.866: E/AndroidRuntime(22739): at com.pasquini.fragment.GetDirectionFragment$GetDirectionTask.onPostExecute(GetDirectionFragment.java:1)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.os.AsyncTask.finish(AsyncTask.java:631)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.os.AsyncTask.access$600(AsyncTask.java:177)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.os.Handler.dispatchMessage(Handler.java:99)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.os.Looper.loop(Looper.java:137)
08-14 12:50:40.866: E/AndroidRuntime(22739): at android.app.ActivityThread.main(ActivityThread.java:4895)
08-14 12:50:40.866: E/AndroidRuntime(22739): at java.lang.reflect.Method.invokeNative(Native Method)
08-14 12:50:40.866: E/AndroidRuntime(22739): at java.lang.reflect.Method.invoke(Method.java:511)
08-14 12:50:40.866: E/AndroidRuntime(22739): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:994)
08-14 12:50:40.866: E/AndroidRuntime(22739): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761)
08-14 12:50:40.866: E/AndroidRuntime(22739): at dalvik.system.NativeStart.main(Native Method).
这里是 fragment 中的代码:
public class GetDirectionFragment extends Fragment {
private Map<Leg, List<Step>> legsCollection;
private ArrayList<Object> legsAndSteps;
private List<Leg> legs;
private List<Poi> pois;
private List<LatLng> polyz;
/**
* Callback interface through which the fragment will report the
* task's progress and results back to the Activity.
*/
public static interface TaskCallbacks {
void onPreExecute();
void onPostExecute();
List<Poi> getListPoiByRoute();
void setLegs(List<Leg> legs, Map<Leg, List<Step>> legsCollection);
void setPolyline(List<LatLng> polyz);
}
private TaskCallbacks callbacks;
private GetDirectionTask getDirectionTask;
/**
* Hold a reference to the parent Activity so we can report the
* task's current progress and results. The Android framework
* will pass us a reference to the newly created Activity after
* each configuration change.
*/
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
callbacks = (TaskCallbacks) activity;
} catch(ClassCastException e) {
throw new ClassCastException(activity.toString() + " must implement TaskCallbacks");
}
pois = callbacks.getListPoiByRoute();
}
/**
* This method will only be called once when the retained
* Fragment is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Retain this fragment across configuration changes.
setRetainInstance(true);
// Create and execute the background task.
getDirectionTask = new GetDirectionTask();
getDirectionTask.execute();
}
/**
* Set the callback to null so we don't accidentally leak the
* Activity instance.
*/
@Override
public void onDetach() {
super.onDetach();
callbacks = null;
}
private class GetDirectionTask extends AsyncTask<Void, Integer, Void> {
@Override
protected void onPreExecute() {
if (callbacks != null) {
callbacks.onPreExecute();
}
}
/**
* Note that we do NOT call the callback object's methods
* directly from the background thread, as this could result
* in a race condition.
*/
@Override
protected Void doInBackground(Void... ignore) {
List<String> lats = new ArrayList<String>();
List<String> longs = new ArrayList<String>();
for(Poi poi: pois) {
lats.add(poi.getCoordinates().getLatitude());
longs.add(poi.getCoordinates().getLongitude());
}
String stringUrl = "http://maps.googleapis.com/maps/api/directions/" +
"json?";
//if(actualLanguage.equals("en")) {
// stringUrl += "language=en_EN";
//} else {
stringUrl += "language=it";
//}
stringUrl+="&mode=walking&units=metric&origin=" +
lats.get(0) + "," +
longs.get(0);
stringUrl += "&destination=" +
lats.get(pois.size()-1) + "," +
longs.get(pois.size()-1) + "&" +
"waypoints=";
for(int i = 1; i<=lats.size()-2 && i<=longs.size()-2; i++) {
stringUrl += lats.get(i)+","+longs.get(i);
if(i==(lats.size()-2) && i==(longs.size()-2)) {
stringUrl += "&sensor=false";
} else {
stringUrl +="|";
}
}
Log.i("urlgoogle", stringUrl);
StringBuilder response = new StringBuilder();
try {
URL url = new URL(stringUrl);
HttpURLConnection httpconn = (HttpURLConnection) url
.openConnection();
if (httpconn.getResponseCode() == HttpURLConnection.HTTP_OK) {
BufferedReader input = new BufferedReader(
new InputStreamReader(httpconn.getInputStream()),
8192);
String strLine = null;
while ((strLine = input.readLine()) != null) {
response.append(strLine);
}
input.close();
}
String jsonOutput = response.toString();
JSONObject jsonObject = new JSONObject(jsonOutput);
// routesArray contains ALL routes
JSONArray routesArray = jsonObject.getJSONArray("routes");
// Grab the first route
JSONObject route = routesArray.getJSONObject(0);
JSONArray legsArray = route.getJSONArray("legs");
legs = new ArrayList<Leg>();
legsAndSteps = new ArrayList<Object>();
String htmlInstructions;
legsCollection = new LinkedHashMap<Leg, List<Step>>();
for(int i=0; i<legsArray.length(); i++) {
List<Step> steps = new ArrayList<Step>();
Leg leg = new Leg();
//int idLeg = 0;
JSONObject legJson = legsArray.getJSONObject(i);
leg.setDistance(legJson.getJSONObject("distance").getString("text"));
leg.setDuration(legJson.getJSONObject("duration").getString("text"));
leg.setEndAddress(legJson.getString("end_address"));
leg.setStartAddress(legJson.getString("start_address"));
leg.setIdLeg(pois.get(i).getId());
leg.setStartPoiName(pois.get(i).getName());
leg.setEndPoiName(pois.get(i+1).getName());
legsAndSteps.add(leg);
JSONArray stepsArray = legJson.getJSONArray("steps");
for(int j=0; j<stepsArray.length(); j++) {
Step step = new Step();
JSONObject stepJson = stepsArray.getJSONObject(j);
step.setDistance(stepJson.getJSONObject("distance").getString("text"));
step.setDuration(stepJson.getJSONObject("duration").getString("text"));
htmlInstructions = android.text.Html.fromHtml(stepJson.getString("html_instructions")).toString();
step.setInstructions(htmlInstructions);
//step.setIdLeg(idLeg);
//Aggiunto per Exp
steps.add(step);
legsAndSteps.add(step);
}
legsCollection.put(leg, steps);
legs.add(leg);
}
JSONObject poly = route.getJSONObject("overview_polyline");
String polyline = poly.getString("points");
polyz = decodePoly(polyline);
callbacks.setLegs(legs, legsCollection);
callbacks.setPolyline(polyz);
} catch (Exception e) {
}
return null;
}
@Override
protected void onPostExecute(Void ignore) {
if (callbacks != null) {
callbacks.onPostExecute();
}
}
}
/* Method to decode polyline points */
private List<LatLng> decodePoly(String encoded) {
[code...]
}
}
这里是 Activity 中的代码:
@Override
public void onPostExecute() {
expListView = (ExpandableListView) findViewById(R.id.lv_routepoi);
ListRouteExpandableAdapter expListAdapter = new ListRouteExpandableAdapter(
getApplicationContext(), legs, legsCollection);
expListView.setAdapter(expListAdapter);
setGroupIndicatorToRight();
expListView.setChildDivider(getResources().getDrawable(R.drawable.divider_route));
[code...]
dialog.dismiss();
}
@Override
public void setLegs(List<Leg> legs, Map<Leg, List<Step>> legsCollection) {
this.legs = legs;
this.legsCollection = legsCollection;
}
@Override
public void setPolyline(List<LatLng> polyz) {
this.polyz = polyz;
}
编辑 #2:我尝试了 Kingfisher 的新解决方案，但 doInBackground 方法中始终存在 NPE。如果我在加载过程中不更改屏幕方向，应用程序不会崩溃并在 ListView 上显示数据。
08-14 17:27:44.897: I/AsyncTask(30604): java.lang.NullPointerException
08-14 17:27:44.897: E/AndroidRuntime(30604): FATAL EXCEPTION: main
08-14 17:27:44.897: E/AndroidRuntime(30604): java.lang.NullPointerException
08-14 17:27:44.897: E/AndroidRuntime(30604): at com.pasquini.activity.RouteActivity.onPostExecute(RouteActivity.java:847)
08-14 17:27:44.897: E/AndroidRuntime(30604): at com.pasquini.fragment.GetDirectionFragment$GetDirectionTask.onPostExecute(GetDirectionFragment.java:253)
08-14 17:27:44.897: E/AndroidRuntime(30604): at com.pasquini.fragment.GetDirectionFragment$GetDirectionTask.onPostExecute(GetDirectionFragment.java:1)
08-14 17:27:44.897: E/AndroidRuntime(30604): at android.os.AsyncTask.finish(AsyncTask.java:631)
08-14 17:27:44.897: E/AndroidRuntime(30604): at android.os.AsyncTask.access$600(AsyncTask.java:177)
08-14 17:27:44.897: E/AndroidRuntime(30604): at android.os.AsyncTask$InternalHandler.handleMessage(AsyncTask.java:644)
08-14 17:27:44.897: E/AndroidRuntime(30604): at android.os.Handler.dispatchMessage(Handler.java:99)
08-14 17:27:44.897: E/AndroidRuntime(30604): at android.os.Looper.loop(Looper.java:137)
08-14 17:27:44.897: E/AndroidRuntime(30604): at android.app.ActivityThread.main(ActivityThread.java:4895)
08-14 17:27:44.897: E/AndroidRuntime(30604): at java.lang.reflect.Method.invokeNative(Native Method)
08-14 17:27:44.897: E/AndroidRuntime(30604): at java.lang.reflect.Method.invoke(Method.java:511)
08-14 17:27:44.897: E/AndroidRuntime(30604): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:994)
08-14 17:27:44.897: E/AndroidRuntime(30604): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:761)
08-14 17:27:44.897: E/AndroidRuntime(30604): at dalvik.system.NativeStart.main(Native Method)
这里是 fragment 中的代码:
public class GetDirectionFragment extends Fragment {
private Map<Leg, List<Step>> legsCollection;
private ArrayList<Object> legsAndSteps;
private List<Leg> legs;
private List<Poi> pois;
private List<LatLng> polyz;
/**
* Callback interface through which the fragment will report the
* task's progress and results back to the Activity.
*/
public static interface TaskCallbacks {
void onPreExecute();
void onPostExecute();
List<Poi> getListPoiByRoute();
void setLegs(List<Leg> legs, Map<Leg, List<Step>> legsCollection);
void setPolyline(List<LatLng> polyz);
}
private TaskCallbacks callbacks;
private GetDirectionTask getDirectionTask;
/**
* Hold a reference to the parent Activity so we can report the
* task's current progress and results. The Android framework
* will pass us a reference to the newly created Activity after
* each configuration change.
*/
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
callbacks = (TaskCallbacks) activity;
} catch(ClassCastException e) {
throw new ClassCastException(activity.toString() + " must implement TaskCallbacks");
}
pois = callbacks.getListPoiByRoute();
}
/**
* This method will only be called once when the retained
* Fragment is first created.
*/
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Retain this fragment across configuration changes.
setRetainInstance(true);
// Create and execute the background task.
getDirectionTask = new GetDirectionTask();
getDirectionTask.execute();
}
/**
* Set the callback to null so we don't accidentally leak the
* Activity instance.
*/
@Override
public void onDetach() {
super.onDetach();
callbacks = null;
}
private class GetDirectionTask extends AsyncTask<Void, Integer, Void> {
@Override
protected void onPreExecute() {
if (callbacks != null) {
callbacks.onPreExecute();
}
}
/**
* Note that we do NOT call the callback object's methods
* directly from the background thread, as this could result
* in a race condition.
*/
@Override
protected Void doInBackground(Void... ignore) {
List<String> lats = new ArrayList<String>();
List<String> longs = new ArrayList<String>();
for(Poi poi: pois) {
lats.add(poi.getCoordinates().getLatitude());
longs.add(poi.getCoordinates().getLongitude());
}
String stringUrl = "http://maps.googleapis.com/maps/api/directions/" +
"json?";
//if(actualLanguage.equals("en")) {
// stringUrl += "language=en_EN";
//} else {
stringUrl += "language=it";
//}
stringUrl+="&mode=walking&units=metric&origin=" +
lats.get(0) + "," +
longs.get(0);
stringUrl += "&destination=" +
lats.get(pois.size()-1) + "," +
longs.get(pois.size()-1) + "&" +
"waypoints=";
for(int i = 1; i<=lats.size()-2 && i<=longs.size()-2; i++) {
stringUrl += lats.get(i)+","+longs.get(i);
if(i==(lats.size()-2) && i==(longs.size()-2)) {
stringUrl += "&sensor=false";
} else {
stringUrl +="|";
}
}
Log.i("urlgoogle", stringUrl);
StringBuilder response = new StringBuilder();
try {
URL url = new URL(stringUrl);
HttpURLConnection httpconn = (HttpURLConnection) url
.openConnection();
if (httpconn.getResponseCode() == HttpURLConnection.HTTP_OK) {
BufferedReader input = new BufferedReader(
new InputStreamReader(httpconn.getInputStream()),
8192);
String strLine = null;
while ((strLine = input.readLine()) != null) {
response.append(strLine);
}
input.close();
}
String jsonOutput = response.toString();
JSONObject jsonObject = new JSONObject(jsonOutput);
// routesArray contains ALL routes
JSONArray routesArray = jsonObject.getJSONArray("routes");
// Grab the first route
JSONObject route = routesArray.getJSONObject(0);
JSONArray legsArray = route.getJSONArray("legs");
legs = new ArrayList<Leg>();
legsAndSteps = new ArrayList<Object>();
String htmlInstructions;
legsCollection = new LinkedHashMap<Leg, List<Step>>();
for(int i=0; i<legsArray.length(); i++) {
List<Step> steps = new ArrayList<Step>();
Leg leg = new Leg();
//int idLeg = 0;
JSONObject legJson = legsArray.getJSONObject(i);
leg.setDistance(legJson.getJSONObject("distance").getString("text"));
leg.setDuration(legJson.getJSONObject("duration").getString("text"));
leg.setEndAddress(legJson.getString("end_address"));
leg.setStartAddress(legJson.getString("start_address"));
leg.setIdLeg(pois.get(i).getId());
leg.setStartPoiName(pois.get(i).getName());
leg.setEndPoiName(pois.get(i+1).getName());
legsAndSteps.add(leg);
JSONArray stepsArray = legJson.getJSONArray("steps");
for(int j=0; j<stepsArray.length(); j++) {
Step step = new Step();
JSONObject stepJson = stepsArray.getJSONObject(j);
step.setDistance(stepJson.getJSONObject("distance").getString("text"));
step.setDuration(stepJson.getJSONObject("duration").getString("text"));
htmlInstructions = android.text.Html.fromHtml(stepJson.getString("html_instructions")).toString();
step.setInstructions(htmlInstructions);
//step.setIdLeg(idLeg);
steps.add(step);
legsAndSteps.add(step);
}
legsCollection.put(leg, steps);
legs.add(leg);
}
JSONObject poly = route.getJSONObject("overview_polyline");
String polyline = poly.getString("points");
polyz = decodePoly(polyline);
setLegs(legs, legsCollection);
setPolyline(polyz);
} catch (Exception e) {
Log.i(TAG, e.toString());
}
return null;
}
@Override
protected void onPostExecute(Void ignore) {
if (callbacks != null) {
callbacks.onPostExecute();
}
}
}
/* Method to decode polyline points */
private List<LatLng> decodePoly(String encoded) {
[code...]
}
public void setLegs(List<Leg> legs, Map<Leg, List<Step>> legsCollection) {
this.legs = legs;
this.legsCollection = legsCollection;
}
public void setPolyline(List<LatLng> polyz) {
this.polyz = polyz;
}
public List<Leg> getLegs() {
return this.legs;
}
public Map<Leg, List<Step>> getMap() {
return this.legsCollection;
}
public List<LatLng> getPolyline() {
return this.polyz;
}
}
这里是 Activity 中的代码:
@Override
protected void onCreate(Bundle savedInstanceState) {
[code...]
FragmentManager fm = getSupportFragmentManager();
getDirectionFragment = (GetDirectionFragment) fm.findFragmentByTag(TASK_FRAGMENT_TAG);
// If the Fragment is non-null, then it is currently being
// retained across a configuration change.
if (getDirectionFragment == null) {
getDirectionFragment = new GetDirectionFragment();
fm.beginTransaction().add(getDirectionFragment, TASK_FRAGMENT_TAG).commit();
[code...]
}
@Override
public void onPostExecute() {
legs = getDirectionFragment.getLegs();
legsCollection = getDirectionFragment.getMap();
polyz = getDirectionFragment.getPolyline();
expListView = (ExpandableListView) findViewById(R.id.lv_routepoi);
ListRouteExpandableAdapter expListAdapter = new ListRouteExpandableAdapter(
getApplicationContext(), legs, legsCollection);
expListView.setAdapter(expListAdapter);
setGroupIndicatorToRight();
expListView.setChildDivider(getResources().getDrawable(R.drawable.divider_route));
[code...]
}
最佳答案
检查此链接:Handling Configuration Changes with Fragments或者您可以使用AsyncTaskLoader 。我建议使用Retained Fragment来处理配置更改。仔细阅读文章。
编辑:不要在doInBackground中调用callback.set函数。当重新创建 Activity 时，您应该找到您的Retained Fragment ，并在onPost函数中尝试使用Retained Fragment的get函数来获取列表结果。
//Activity recreated
FragmentManager fm = getFragmentManager();
mTaskFragment = (TaskFragment) fm.findFragmentByTag("task");
//onPost method
yourList = mTaskFragment.getLegsAndMoveList();
// Do lisview data changing here
希望这有帮助。
关于android - AsyncTask 和方向变化，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/18214293/