Firebase-获取所有子项并添加到ListView

Question

我在一个活动中有4个片段，即数据库片段，当前包含ListView，它将查询Firebase以从父节点“资产”获取子代。另外，ListView具有一个自定义适配器，该适配器使其具有标题和副标题。

这是数据库结构

这是主要活动：

/var/www/xyz_pythonanywhere_com_wsgi.py

这是数据库片段：

private var toolbar: ActionBar? = null

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    toolbar = supportActionBar

    toolbar?.title = resources.getString(R.string.navigation_database)
    loadFragment(DatabaseFragment())

    setNavigation()
}
private fun setNavigation(){
    val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavigation)
    bottomNavigationView.setOnNavigationItemSelectedListener { item ->

        var fragment: Fragment

        when (item.itemId) {
            R.id.navigation_database -> {
                toolbar?.title = resources.getString(R.string.navigation_database)
                fragment = DatabaseFragment()
                loadFragment(fragment)
            }
            R.id.navigation_track -> {
                toolbar?.title = resources.getString(R.string.navigation_tracking)
                fragment = TrackingFragment()
                loadFragment(fragment)
            }
            R.id.navigation_activities -> {
                toolbar?.title = resources.getString(R.string.navigation_activities)
                fragment = ActivitiesFragment()
                loadFragment(fragment)
            }
            R.id.navigation_references -> {
                toolbar?.title = resources.getString(R.string.navigation_references)
                fragment = ReferencesFragment()
                loadFragment(fragment)
            }
        }
        true
    }
}
private fun loadFragment(fragment: Fragment){
    val fragmentTransaction = supportFragmentManager.beginTransaction()
    fragmentTransaction.replace(R.id.childLayout, fragment)
    fragmentTransaction.addToBackStack(null)
    fragmentTransaction.commit()
}

这是自定义适配器：

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    val rootView = inflater.inflate(R.layout.fragment_database, container, false)

    val titleList = ArrayList<String>()
    val subtitleList = ArrayList<String>()

    val databaseReference = FirebaseDatabase.getInstance().getReference("Assets")
    databaseReference.addValueEventListener(object : ValueEventListener{
        override fun onCancelled(databaseError: DatabaseError) {
        }

        override fun onDataChange(dataSnapshot: DataSnapshot) {
            for(childSnapshot: DataSnapshot in dataSnapshot.children){
                titleList.add(childSnapshot.key.toString())
                subtitleList.add("subtitle")
            }
        }

    })

    val listView = rootView.findViewById(R.id.databaseListView) as ListView
    val adapter = DatabaseListAdapter(activity as MainActivity, titleList, subtitleList)
    listView.adapter = adapter

    return rootView
}

Firebase数据库规则：

public Context context;
public ArrayList<String> titleList;
public ArrayList<String> subtitleList;

public DatabaseListAdapter(Context context, ArrayList<String> titleList, ArrayList<String> subtitleList){
    this.context = context;
    this.titleList = titleList;
    this.subtitleList = subtitleList;
}

@Override
public int getCount() {
    return titleList.size();
}

@Override
public Object getItem(int position) {
    return titleList.get(position);
}

@Override
public long getItemId(int position) {
    return position;
}

@Override
public View getView(int position, View convertView, ViewGroup parent) {
    View rootView = LayoutInflater.from(context).inflate(R.layout.layout_listview_database, parent, false);

    TextView titleView = rootView.findViewById(R.id.titleView);
    TextView subtitleView = rootView.findViewById(R.id.subtitleView);

    titleView.setText(titleList.get(position));
    subtitleView.setText(subtitleList.get(position));

    return rootView;
}

Answer 1

在override fun onDataChange(dataSnapshot: DataSnapshot)中，将所有内容添加到列表后，您需要致电adapter.notifyDataSetChanged()。

您可以保留对适配器的全局var引用，也可以按ID查找回收者视图并获取其适配器。

您可能还想先清除列表，然后再向其中添加内容。