ArrayList在使用后不会更新.clear（）

我是Android开发新手，请耐心等待。ArrayList在使用后不会更新.clear（）

我有一个自定义ArrayAdapter，我想通过向下刷新进行更新。

我明白，为了做到这一点，我需要：

明确表示对我的数据（与.clear（））ArrayList的
更新与新数据的ArrayList（使用getAbsentTeachers （）上一个ArrayAdapter

后我清除ArrayList中，调用getAbsentTeachers方法）

使用notifyDataSetChanged（）（）和notifyDataSetChanged（）该ArrayList似乎保持为空è尽管getAbsentTeachers（）是beeing调用。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填充ArrayList，但当我再次调用它来更新ArrayList时，它似乎不工作。

有关数组为何不更新的任何想法？

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; 

     } 

    } 
}

来源

2016-11-14 AngryMan Studios

将这两行移到Parse调用的done中的if-else之后。

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

您目前没有在通知适配器之前等待Parse调用完成。

另一种解决方案是改变

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

到

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

来源

2016-11-14 22:59:58

忘了考虑到这一点 - 谢谢！ –

ArrayList在使用后不会更新.clear（）

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