Question

此图片显示没有元素（活动），如何解决？我想这很简单，请帮助我。 Click Here!

这是我的主要活动。 java *请评论以查看更多文件

| Code | Name | Total | Trading Account | Count |
|11475 | SANDY| 697   | Z07640C         | 422   |
|      |      |       | Z04276B         | 93    |
...
|13139 |Sran  | 34    | Z32421A         | 2     |
|      |      |       | Z43487B         | 24    |
...

这是我的activity_main.xml *请评论您要查看的文件

    package com.example.jdev.trytry;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.MenuItem;

import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity {

    private RecyclerView recyclerView;
    private List<userModel> result;
    private userAdapter adapter;

    private FirebaseDatabase database;
    private DatabaseReference reference;

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

            database = FirebaseDatabase.getInstance();
            reference = database.getReference("users");


            result = new ArrayList<>();

            recyclerView = (RecyclerView) findViewById(R.id.user_list);
            recyclerView.setHasFixedSize(true);
            LinearLayoutManager lin = new LinearLayoutManager(this);
            lin.setOrientation(LinearLayoutManager.VERTICAL);

            recyclerView.setLayoutManager(lin);

            adapter = new userAdapter(result);
            recyclerView .setAdapter(adapter);

            updateList();

    }

    @Override
    public boolean onContextItemSelected (MenuItem item){

        switch (item.getItemId()){
            case 0:
                break;

            case 1:
                break;
        }
        return super.onContextItemSelected(item);
    }


    private void updateList(){
        reference.addChildEventListener(new ChildEventListener(){

            @Override
            public void onChildAdded (DataSnapshot dataSnapshot, String a){

                result.add(dataSnapshot.getValue(userModel.class));
                adapter.notifyDataSetChanged();
            }

            @Override
            public void onChildChanged(DataSnapshot dataSnapshot, String a){

                userModel model = dataSnapshot.getValue(userModel.class);

                int index = getItemIndex(model);
                result.set(index, model);
                adapter.notifyItemChanged(index);

            }

            @Override
            public void onChildRemoved(DataSnapshot dataSnapshot){

                userModel model = dataSnapshot.getValue(userModel.class);


                int index = getItemIndex(model);
                result.remove(index);
                adapter.notifyItemRemoved(index);

            }

            @Override
            public void onChildMoved (DataSnapshot dataSnapshot, String a){

            }

            @Override
            public void onCancelled (DatabaseError databaseError){

            }
        });
    }

    private int getItemIndex(userModel user){
        int index = -1;

        for (int i = 0; i < result.size(); i++){
            if(result.get(i).key.equals(user.key))
                index = i;

                break;
        }
        return index;
    }


}

这是userAdapter.java

  <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.jdev.trytry.MainActivity">

  <android.support.v7.widget.RecyclerView
      android:id="@+id/user_list"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      />

</RelativeLayout>

如果您需要其他文件，请发表评论，谢谢！

Answer 1

如果为空则检查结果列表数组大小，则不会显示任何内容。当您获取数据时，数据会添加到列表中，然后在定义适配器并将适配器设置为recyclerview之后。比如制作一套适配器方法

    private void setAdapter() {
    if (adapter == null) {
        if (!result.isEmpty()) {

            adapter = new userAdapter(result);
            recyclerView.setAdapter(adapter);
            adapter.notifyDataSetChanged();
        }
    } else {
        adapter.notifyDataSetChanged();
    }
}

之后调用上面的方法定义方法updateList（），并从onCreate（）方法中删除下面的代码

        adapter = new userAdapter(result);
        recyclerView .setAdapter(adapter);

总是在您获得数据的时候将数据绑定到回收站视图。

应用程序显示没有元素（活动），如何解决？

1 个答案: