在我更改Android应用程序的设计之前，我想知道是否可以保留片段的状态，包括重新创建时收集的所有数据。在我的片段中，我有一个异步任务，用于收集json的正确数据，并将它们发布到不同的卡片视图中。这是我的代码：
LatestEventsFragment.java
public class LatestEventsFragment extends Fragment {
RecyclerView recyclerView;
RecyclerView.Adapter adapter;
ArrayList<Event> arrayList = new ArrayList();
ProgressDialog progressDialog;
@Nullable
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
setRetainInstance(true);
View view = inflater.inflate(R.layout.events_list, container, false);
LinearLayoutManager linearLayoutManager = new LinearLayoutManager(getActivity());
recyclerView = (RecyclerView)view.findViewById(R.id.events_recycler);
linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recyclerView.setLayoutManager(linearLayoutManager);
recyclerView.setHasFixedSize(true);
adapter = new EventsRecyclerAdapter(arrayList);
recyclerView.setAdapter(adapter);
EventsAsyncTask eventsAsyncTask = new EventsAsyncTask();
eventsAsyncTask.execute();
return view;
}
class EventsAsyncTask extends AsyncTask<String, Event, String> {
@Override
protected void onPreExecute() {
progressDialog = new ProgressDialog(getActivity());
progressDialog.setTitle("Please wait...");
progressDialog.setMessage("Loading");
progressDialog.setIndeterminate(true);
progressDialog.setCancelable(false);
progressDialog.show();
}
@Override
protected void onPostExecute(String s) {
progressDialog.dismiss();
}
@Override
protected void onProgressUpdate(Event... values) {
arrayList.add(values[0]);
adapter.notifyDataSetChanged();
}
@Override
protected String doInBackground(String... params) {
try {
ServerConfig serverConfig = new ServerConfig();
URL url = new URL(serverConfig.getEvents_url());
HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = httpURLConnection.getInputStream();
BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
StringBuilder stringBuilder = new StringBuilder();
String line = "";
while((line = bufferedReader.readLine()) != null){
stringBuilder.append(line+"\n");
}
httpURLConnection.disconnect();
String json_string = stringBuilder.toString().trim();
JSONObject jsonObject = new JSONObject(json_string);
JSONArray jsonArray = jsonObject.getJSONArray("server_response");
int count = 0;
while(count<jsonArray.length()){
JSONObject JO = jsonArray.getJSONObject(count);
count++;
String jsonString = JO.get("image").toString();
byte[] temp = Base64.decode(jsonString.getBytes(), Base64.DEFAULT);
Bitmap decodedByte = BitmapFactory.decodeByteArray(temp, 0, temp.length);
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.US);
dateFormat.setTimeZone(TimeZone.getTimeZone("UCT"));
Date date = dateFormat.parse(JO.getString("date_posted"));
Date server_date = dateFormat.parse(JO.getString("server_date"));
Event event = new Event(JO.getString("name"), decodedByte, JO.getInt("views"), date, server_date);
publishProgress(event);
Thread.sleep(500);
}
} catch (Exception e){
e.printStackTrace();
}
return null;
}
}
}
EventsRecyclerAdapter.java
public class EventsRecyclerAdapter extends RecyclerView.Adapter<EventsRecyclerAdapter.RecyclerViewHolder>{
ArrayList<Event> arrayList = new ArrayList<>();
public EventsRecyclerAdapter(ArrayList<Event> arrayList){
this.arrayList = arrayList;
}
@Override
public RecyclerViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.latest_events_card, parent, false);
return new RecyclerViewHolder(view);
}
@Override
public void onBindViewHolder(RecyclerViewHolder holder, int position) {
Event event = arrayList.get(position);
try{
String views = String.valueOf(event.getViews())+" views";
String date_string = getTime(event.getServer_date().getTime() - event.getDate_posted().getTime());
holder.name.setText(event.getName());
holder.image.setImageBitmap(event.getImage());
holder.views.setText(views);
holder.date_posted.setText(date_string);
}catch (Exception e){
e.printStackTrace();
}
}
private String getTime(Long time_difference){
long secondsInMilli = 1000;
long minutesInMilli = secondsInMilli * 60;
long hoursInMilli = minutesInMilli * 60;
long daysInMilli = hoursInMilli * 24;
long elapsedDays = time_difference / daysInMilli;
int daysInt = (int)elapsedDays;
time_difference = time_difference % daysInMilli;
long elapsedHours = time_difference / hoursInMilli;
int hoursInt = (int)elapsedHours;
time_difference = time_difference % hoursInMilli;
long elapsedMinutes = time_difference / minutesInMilli;
int minutesInt = (int)elapsedMinutes;
//time_difference = time_difference % minutesInMilli;
//long elapsedSeconds = time_difference / secondsInMilli;
String date_string = String.valueOf(daysInt);
if(daysInt > 0) {
if (daysInt == 1) {
date_string = "1 Day";
} else if (daysInt > 1) {
date_string = daysInt + " Days";
}
}else if(hoursInt > 0){
if(hoursInt == 1){
date_string = "1 Hour ";
if(minutesInt > 1){
date_string = date_string + minutesInt + " Minutes";
}
} else if(hoursInt > 1){
date_string = hoursInt + " Hours ";
if(minutesInt > 1){
date_string = date_string + minutesInt + " Minutes";
}
}
}else if(minutesInt > 0){
if (minutesInt == 1) {
date_string = "1 Minute";
} else if (minutesInt > 1) {
date_string = minutesInt + " Minutes";
}
}
return date_string + " ago";
}
@Override
public int getItemCount() {
return arrayList.size();
}
public static class RecyclerViewHolder extends RecyclerView.ViewHolder{
protected TextView name, views, date_posted, start_date, end_date;
protected ImageView image;
public RecyclerViewHolder(View v){
super(v);
name = (TextView)v.findViewById(R.id.name);
image = (ImageView)v.findViewById(R.id.thumbnail);
views = (TextView)v.findViewById(R.id.views);
date_posted = (TextView)v.findViewById(R.id.date_posted);
}
}
}
最后 Events.java
public class Event {
private int id;
private String name;
private String description;
private String start_date;
private String end_date;
private double entrance_fee;
private Bitmap image;
private int views;
private Date date_posted;
private Date server_date;
public Event(String name, Bitmap image, int views, Date date_posted, Date server_date){
//int id, String name, , String start_date, double entrance_fee, Bitmap image, int views
this.setDescription(description);
this.setEnd_date(end_date);
this.setEntrance_fee(entrance_fee);
this.setId(id);
this.setImage(image);
this.setName(name);
this.setViews(views);
this.setStart_date(start_date);
this.setDate_posted(date_posted);
this.setServer_date(server_date);
}
public Date getServer_date() {
return server_date;
}
public void setServer_date(Date server_date) {
this.server_date = server_date;
}
public Date getDate_posted() {
return date_posted;
}
public void setDate_posted(Date date_posted) {
this.date_posted = date_posted;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description;
}
public String getStart_date() {
return start_date;
}
public void setStart_date(String start_date) {
this.start_date = start_date;
}
public String getEnd_date() {
return end_date;
}
public void setEnd_date(String end_date) {
this.end_date = end_date;
}
public double getEntrance_fee() {
return entrance_fee;
}
public void setEntrance_fee(double entrance_fee) {
this.entrance_fee = entrance_fee;
}
public Bitmap getImage() {
return image;
}
public void setImage(Bitmap image) {
this.image = image;
}
public int getViews() {
return views;
}
public void setViews(int views) {
this.views = views;
}
}
答案 0 :(得分：0)
您可以在片段中使用onSaveInstanceState来保存数据，然后查看savedInstanceState中的onCreateView变量，看看它是否有数据。如果是，只需检索数据即可重新创建视图。
内部碎片：
@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
// Always call the superclass so it can save the view hierarchy state
super.onSaveInstanceState(savedInstanceState);
if(mDataToSave != null) {
savedInstanceState.putString("myData", mDataToSave);
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
if(savedInstanceState != null){
String restoredData = (String)savedInstanceState.getString("myData");
//do something with restoredData
}
return rootView;
}
请记住将put和get savedInstanceState.putString()更改为savedInstanceState.put<WhateverYourDataTypeIs>()
如果您要在主要活动中通过片段交易添加片段，请确保仅在主要活动savedInstanceState为空时才添加片段。这样，如果片段已被添加，您将无法替换片段。
内部活动（如果您有片段交易）：
if(savedInstanceState == null) {
Fragment newFragment = new MyFragment();
//add main fragment to fragment frame
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction().add(R.id.fragment_container, newFragment).commit();
}