使用来自 firebase 的数据创建 ExpandableListView

Question

我正在创建一个任务管理器应用。我在ExpandableListView 中显示这些任务时遇到问题，我正在使用它，因为每个任务都可能有子任务。这是我的数据库结构：

.

ExpandableListView 适配器可能运行良好。但是我在 fillData() 方法中从 firebase 读取数据时遇到问题。

Activity 与 ExpandableListView：

public class Tasks extends AppCompatActivity {

    ExpandableListView expandableListView;
    CustomExpandableListAdapter expandableListAdapter;

    List<String> tasks;
    Map<String, List<String>> subtasks;

    private FirebaseDatabase firebasedatabase;
    private DatabaseReference databaseReference;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tasks);

        BottomNavigationView bottomNav = findViewById(R.id.bottom_nav);
        bottomNav.setSelectedItemId(R.id.tasks);
        expandableListView = (ExpandableListView) findViewById(R.id.tasks_list);

        firebasedatabase = FirebaseDatabase.getInstance();
        databaseReference = firebasedatabase.getReference("Tasks");
        fillData();
        expandableListAdapter = new CustomExpandableListAdapter(this, tasks, subtasks);
        expandableListView.setAdapter(expandableListAdapter);




        bottomNav.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem item) {
                switch (item.getItemId()){
                    case R.id.notes:
                        startActivity(new Intent(getApplicationContext(), Notes.class));
                        overridePendingTransition(0,0);
                        return true;
                    case R.id.tasks:
                        return true;
                    case R.id.goals:
                        startActivity(new Intent(getApplicationContext(), Goals.class));
                        overridePendingTransition(0,0);
                        return true;
                    case R.id.statistics:
                        startActivity(new Intent(getApplicationContext(), Statistics.class));
                        overridePendingTransition(0,0);
                        return true;
                    case R.id.add:
                        startActivity(new Intent(getApplicationContext(), Add.class));
                        overridePendingTransition(0,0);
                        return true;

                }
                return false;
            }
        });

    }

    public void fillData()
    {
        databaseReference.addValueEventListener(new ValueEventListener() {

            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                if(tasks.size() > 0) tasks.clear();
                for(DataSnapshot ds : dataSnapshot.getChildren())
                {
                  String taskName = (String) ds.child("Tasks").getValue();
                  tasks.add(taskName);
                }

                expandableListAdapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });
    }
}

ExpandableListView 适配器：

public class CustomExpandableListAdapter extends BaseExpandableListAdapter {

private Context context;
private List<String> listHeader;
private Map<String, List<String>> listChildren;
public CustomExpandableListAdapter(Context context, List<String> listHeader, Map<String, List<String>> listChildren){
    this.context = context;
    this.listHeader = listHeader;
    this.listChildren = listChildren;
}

@Override
public int getGroupCount() {
    return this.listHeader.size();
}

@Override
public int getChildrenCount(int groupPosition) {
    return this.listChildren.get(listHeader.get(groupPosition)).size();
}

@Override
public Object getGroup(int groupPosition) {
    return this.listHeader.get(groupPosition);
}

@Override
public Object getChild(int groupPosition, int childPosition) {
    return this.listChildren.get(this.listHeader.get(groupPosition));
}

@Override
public long getGroupId(int groupPosition) {
    return groupPosition;
}

@Override
public long getChildId(int groupPosition, int childPosition) {
    return childPosition;
}

@Override
public boolean hasStableIds() {
    return false;
}

@Override
public View getGroupView(int groupPosition, boolean isExpanded, View convertView, ViewGroup parent) {
    String header = (String) getGroup(groupPosition);

    if(convertView == null)
    {
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.list_view_header, null);
    }

    TextView headerOfGroup = (TextView) convertView.findViewById(R.id.header_text);
    headerOfGroup.setText(header);
    return convertView;
}

@Override
public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent) {
    String child = (String) getChild(groupPosition, childPosition);

    if(convertView == null)
    {
        LayoutInflater inflater = (LayoutInflater) context.getSystemService(context.LAYOUT_INFLATER_SERVICE);
        convertView = inflater.inflate(R.layout.list_view_child, null);
    }

    TextView childText = (TextView) convertView.findViewById(R.id.child_text);
    childText.setText(child);
    return convertView;
}

@Override
public boolean isChildSelectable(int groupPosition, int childPosition) {
    return true;
}

}

Answer 1

据我所知，您问题中的相关代码是：

firebasedatabase = FirebaseDatabase.getInstance();
databaseReference = firebasedatabase.getReference("Tasks");
databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        if(tasks.size() > 0) tasks.clear();
        for(DataSnapshot ds : dataSnapshot.getChildren())
        {
          String taskName = (String) ds.child("Tasks").getValue();
          tasks.add(taskName);
        }

        expandableListAdapter.notifyDataSetChanged();
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
    }
});

您的代码将侦听器附加到/Tasks，然后循环其子节点，并获取每个子节点的Tasks 子节点。但是，如果我们查看您的数据库结构，则每个任务下都没有 Tasks 子节点。所以这可能会导致一个空项目列表，对于/Tasks 的每个子节点一次

---

如果您想显示/Tasks 的每个子节点的键（所以屏幕截图中的make a aolication 和Shoping），您需要使用每个子节点的getKey()：

firebasedatabase = FirebaseDatabase.getInstance();
databaseReference = firebasedatabase.getReference("Tasks");
databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        if(tasks.size() > 0) tasks.clear();
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String taskName = ds.getKey();
            tasks.add(taskName);
        }

        expandableListAdapter.notifyDataSetChanged();
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException()
    }
});

---

如果要显示每个子节点的Subtasks 下的所有值，则需要为此添加另一个嵌套循环：

firebasedatabase = FirebaseDatabase.getInstance();
databaseReference = firebasedatabase.getReference("Tasks");
databaseReference.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        if(tasks.size() > 0) tasks.clear();
        for(DataSnapshot taskSnapshot: dataSnapshot.getChildren()) {
            DataSnapshot subtasksSnapshot = taskSnapshot.child("Subtasks");
            for(DataSnapshot subtaskSnapshot: subtasksSnapshot.getChildren()) {
                String taskName = subtaskSnapshot.getValue(String.class);
                tasks.add(taskName);
            }
        }

        expandableListAdapter.notifyDataSetChanged();
    }

    @Override
    public void onCancelled(@NonNull DatabaseError databaseError) {
        throw databaseError.toException()
    }
});