使用.clear()后ArrayList不更新 [英] ArrayList not updating after using .clear()
问题描述
我是Android开发的新手，所以请多多包涵.
I'm new to Android development, so please bear with me.
我有一个自定义ArrayAdapter，我想通过向下滑动以刷新来进行更新.
I have a custom ArrayAdapter which I want to update by swiping down to refresh.
我了解要执行此操作，我需要:
I understand that in order to do this I need to:
- 使用.clear()清除保存我的数据的ArrayList
- 使用新数据(使用getAbsentTeachers()方法)更新ArrayList
- 在ArrayAdapter上使用notifyDataSetChanged()
清除了ArrayList之后，调用getAbsentTeachers()和notifyDataSetChanged()，即使getAbsentTeachers()被调用，ArrayList仍保持为空.我知道这是因为ListView中什么都没有显示.
After I clear the ArrayList, call getAbsentTeachers() and notifyDataSetChanged() the ArrayList appears to remain empty even though getAbsentTeachers() is beeing called. I know this because nothing is displayed in my ListView.
getAbsentTeachers()会在我的应用程序首次启动时很好地填充ArrayList，但是当我再次调用它以更新ArrayList时，它似乎无法正常工作.
getAbsentTeachers() populates the ArrayList fine when my app is first launched however it doesn't seem to work when I call it again to update the ArrayList.
关于为什么数组不更新的任何想法吗?
Any ideas as to why the array is not beeing updated?
MainActivity.java: 软件包uk.co.bobsmith.drawview.drawviewtest;
MainActivity.java: package uk.co.bobsmith.drawview.drawviewtest;
public class MainActivity extends AppCompatActivity
implements NavigationView.OnNavigationItemSelectedListener {
private ArrayList<Absent> absences = new ArrayList<>();
private SwipeRefreshLayout swipeContainer;
@Override
protected void onCreate(Bundle savedInstanceState) {
//---------------------INITIALISING PARSE-------------------------------
Parse.enableLocalDatastore(this);
// Add your initialization code here
Parse.initialize(new Parse.Configuration.Builder(getApplicationContext())
//Information obscured for privacy - tested and working though.
.applicationId("")
.clientKey(null)
.server("")
.build()
);
ParseUser.enableAutomaticUser();
ParseACL defaultACL = new ParseACL();
// Optionally enable public read access.
// defaultACL.setPublicReadAccess(true);
ParseACL.setDefaultACL(defaultACL, true);
ParseInstallation.getCurrentInstallation().saveInBackground();
ParsePush.subscribeInBackground("Absent");
//-----------------------CREATE ADAPTER OBJECT--------------------------------
getAbsentTeachers();
final ListView lv = (ListView)findViewById(R.id.listView);
final ArrayAdapter<Absent> adapter = new absenceArrayAdapter(this, 0, absences);
lv.setAdapter(adapter);
swipeContainer = (SwipeRefreshLayout) findViewById(R.id.swipeContainer);
// Setup refresh listener which triggers new data loading
swipeContainer.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
@Override
public void onRefresh() {
// Code to refresh the list.
absences.clear();
getAbsentTeachers();
adapter.notifyDataSetChanged();
swipeContainer.setRefreshing(false);
// Call swipeContainer.setRefreshing(false) when finished.
}
});
}
// Populates absences ArrayList with absence data
public void getAbsentTeachers() {
ParseQuery<ParseObject> query = ParseQuery.getQuery("Absences");
query.findInBackground(new FindCallback<ParseObject>() {
@Override
public void done(List<ParseObject> objects, ParseException e) {
if(e == null){
for(ParseObject object : objects){
String name = String.valueOf(object.get("name"));
Log.i("Name", name);
String desc = String.valueOf(object.get("description"));
Log.i("Description", desc);
absences.add(new Absent(name, desc, "employees"));
}
} else {
Log.i("Get data from parse", "There was an error getting data!");
e.printStackTrace();
}
}
});
}
//custom ArrayAdapter
class absenceArrayAdapter extends ArrayAdapter<Absent> {
private Context context;
private List<Absent> absencesList;
public absenceArrayAdapter(Context context, int resource, ArrayList<Absent> objects) {
super(context, resource, objects);
this.context = context;
this.absencesList = objects;
}
public View getView(int position, View convertView, ViewGroup parent) {
//get the property we are displaying
Absent teacher = absencesList.get(position);
//get the inflater and inflate the XML layout for each item
LayoutInflater inflater = (LayoutInflater) context.getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
View view = inflater.inflate(R.layout.custom_listview, null);
TextView name = (TextView) view.findViewById(R.id.name);
TextView description = (TextView) view.findViewById(R.id.description);
ImageView teacherImage = (ImageView) view.findViewById(R.id.imageView);
String teacherName = teacher.getTeacherName();
name.setText(teacherName);
int descriptionLength = teacher.getDescription().length();
if(descriptionLength >= 75){
String descriptionTrim = teacher.getDescription().substring(0, 75) + "...";
description.setText(descriptionTrim);
}else{
description.setText(teacher.getDescription());
}
return view;
}
}
}
推荐答案
将这两行移动到Parse调用的done中的if-else之后.
Move these two lines to after the if-else within the done of the Parse call.
adapter.notifyDataSetChanged();
swipeContainer.setRefreshing(false);
您当前不等待解析调用完成，然后再通知适配器.
You currently are not waiting for the Parse call to finish before notifying the adapter.
另一种解决方案是更改
absences.add(new Absent(name, desc, "employees"));
到
adapter.add(new Absent(name, desc, "employees"));
这篇关于使用.clear()后ArrayList不更新的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
