ListView 不显示添加的项目

Posted 2023-04-19

【中文标题】ListView 不显示添加的项目

【英文标题】：ListView is not showing items that are added

【发布时间】：2020-09-02 05:47:11

【问题描述】：

编辑

收到错误，原来是模拟器 API 版本的问题。在更高的 API 版本中工作正常

我是 android 开发的新手，我正在尝试构建一个简单的待办事项列表，当单击按钮时，项目将被添加到 ListView。问题是，这些项目没有显示在列表视图中，尽管它们被添加和删除。请帮我找出我做错了什么。

这是我的 activity_main.xml 文件

<android.support.constraint.ConstraintLayout 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_
    android:layout_
    tools:context="com.example.erfan.todolist.MainActivity">

    <RelativeLayout
        android:layout_
        android:layout_
        tools:layout_editor_absoluteX="8dp"
        tools:layout_editor_absoluteY="8dp">

        <EditText
            android:id="@+id/editTextAddItem"
            android:hint="Enter Item"
            android:layout_
            android:layout_
            android:layout_weight="4"
            android:layout_alignParentTop="true"
            android:layout_alignParentStart="true" />

        <Button
            android:id="@+id/buttonAddItem"
            android:text="Add"
            android:layout_
            android:layout_
            android:layout_alignParentTop="true"
            android:layout_alignParentEnd="true" />

        <ListView
            android:id="@+id/listView"
            android:layout_
            android:layout_
            android:layout_alignParentStart="true"
            android:layout_below="@+id/editTextAddItem"
            android:layout_marginTop="23dp" />

    </RelativeLayout>
</android.support.constraint.ConstraintLayout>

这是我的 MainActivity.java 文件

package com.example.erfan.todolist;

import android.app.ListActivity;
import android.content.Context;
import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Adapter;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.Toast;

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity 

    EditText vEditTextAddItem;
    Button vButtonAddItem;
    ListView vListViewItemList;
    ArrayList<String> items;
    ArrayAdapter<String> adapter;
    public static final String FILENAME = "data.dat";

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

        vEditTextAddItem = (EditText) findViewById(R.id.editTextAddItem);
        vButtonAddItem = (Button) findViewById(R.id.buttonAddItem);
        vListViewItemList = (ListView) findViewById(R.id.listView);

        items = readData(getApplicationContext());

        adapter = new ArrayAdapter<String>(getApplicationContext(), R.layout.support_simple_spinner_dropdown_item, items);
        vListViewItemList.setAdapter(adapter);

        vButtonAddItem.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View v) 
                switch (v.getId()) 
                    case R.id.buttonAddItem:
                        String itemEntered = vEditTextAddItem.getText().toString();
                        adapter.add(itemEntered);
                        vEditTextAddItem.setText("");

                        writeData(items, getApplicationContext());

                        Toast.makeText(getApplicationContext(), "Item is added", Toast.LENGTH_SHORT).show();
                        break;
                
            
        );

        vListViewItemList.setOnItemClickListener(new AdapterView.OnItemClickListener() 
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) 
                items.remove(position);
                adapter.notifyDataSetChanged();
                Toast.makeText(getApplicationContext(), "Item Deleted", Toast.LENGTH_SHORT).show();
            
        );

    

    public static void writeData(ArrayList<String> items, Context context) 
        try 
            FileOutputStream fileOutputStraStream = context.openFileOutput(FILENAME, Context.MODE_PRIVATE);
            ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStraStream);
            objectOutputStream.writeObject(items);
            objectOutputStream.close();
         catch (FileNotFoundException e) 
            e.printStackTrace();
         catch (IOException e) 
            e.printStackTrace();
        
    

    public static ArrayList<String> readData(Context context) 

        ArrayList<String> itemList = null;
        try 
            FileInputStream fileInputStream = context.openFileInput(FILENAME);
            ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
            itemList = (ArrayList<String>) objectInputStream.readObject();
         catch (FileNotFoundException e) 
            itemList = new ArrayList<>();
            e.printStackTrace();
         catch (IOException e) 
            e.printStackTrace();
         catch (ClassNotFoundException e) 
            itemList = new ArrayList<>();
            e.printStackTrace();
        

        return itemList;
    

我也附上了模拟器的截图

添加项目后，ListView 中不显示任何项目。

【问题讨论】：

你错过了 adapter.notifyDataSetChanged();在案例的底部 R.id.buttonAddItem: String itemEntered = vEditTextAddItem.getText().toString();适配器.add(itemEntered); vEditTextAddItem.setText(""); adapter.notifyDataSetChanged();

【参考方案1】：

收到错误，原来是模拟器 API 版本的问题。在更高的 API 版本中工作正常