使用 .clear() 后 ArrayList 不更新

Question

我是 Android 开发的新手，所以请多多包涵。

我有一个自定义的 ArrayAdapter，我想通过向下滑动刷新来更新它。

我明白，为了做到这一点，我需要：

清除保存我的数据的 ArrayList（使用 .clear()）
用新数据更新 ArrayList（使用 getAbsentTeachers() 方法）
在 ArrayAdapter 上使用 notifyDataSetChanged()

在我清除 ArrayList、调用 getAbsentTeachers() 和 notifyDataSetChanged() 之后，即使正在调用 getAbsentTeachers()，ArrayList 似乎仍为空。我知道这是因为我的 ListView 中没有显示任何内容。

getAbsentTeachers() 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来更新 ArrayList 时它似乎不起作用。

关于为什么数组没有更新的任何想法？

MainActivity.java: 包裹 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;

        }

    }
}

Answer 1

将这两行移动到 Parse 调用的 done 中的 if-else 之后。

adapter.notifyDataSetChanged();
swipeContainer.setRefreshing(false);

您目前没有等待 Parse 调用完成才通知适配器。

另一个解决方案是改变

absences.add(new Absent(name, desc, "employees"));

到

adapter.add(new Absent(name, desc, "employees"));

使用 .clear() 后 ArrayList 不更新

ArrayList not updating after using .clear()

java

android

parse-platform