android笔记：ListView及ArrayAdapter

Posted 2020-08-01 乐之者

ListView用于展示大量数据，而数据无法直接传递给ListView，需要借助适配器adapter来完成.

ArrayAdapter是最常用的adapter,可以通过泛型来指定要适配的数据类型.常见的Adapter还有BaseAdapter,SimpleAdapter,CursorAdapter等

ArrayAdapter构造方法的参数如下：

android.widget.ArrayAdapter.ArrayAdapter<String>(Context context, int resource, String[] objects)

  android.widget.ArrayAdapter.ArrayAdapter(Context context, int resource, List<T> objects)

构造函数常见的参数解析如下：

Context context：当前的上下文环境;

int resource ：指定布局文件中包含的TextView资源的ID,常用的有android.R.layout.simple_list_item_1，

android.R.layout.simple_list_item_1是一个android内置的布局文件，只有一个TextView，用于简单显示文本;

String[] objects:要在视图里显示的字符串数组

List<T> objects:要在视图里显示的集合

 

ListView的使用步骤如下：

1.在Activity的xml布局中加入ListView控件

2.在另一个xml布局中写出ListView的item组成，比如说将ListView的每一个item设置为一个ImageView和一个TextView

3.继承Adapter，重写getItem()，getView()等方法;

4.在Activity中通过findViewById()加载ListView后，实例化Adapter，然后为ListView加载Adapter

 

具体代码如下所示：

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <ListView 
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent" >    
    </ListView>

</RelativeLayout>

 

list_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
     android:layout_width="wrap_content"
     android:layout_height="wrap_content"
     android:id="@+id/image"/>
    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/text"/>
</LinearLayout>

 

MainActivity.java

package com.example.listviewdemo;

import android.content.Context;
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

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

public class MainActivity extends Activity {
    private ArrayList<Data> dataList;
    private ListView listView;
    private  MyAdapter adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initData();
        //新建数组适配器
        adapter=new MyAdapter(MainActivity.this , R.layout.list_item , dataList);
        //加载列表视图
        listView=(ListView)findViewById(R.id.list_view);
        //将构建好的适配器对象传递进去，建立ListView和数据之间的关联
        listView.setAdapter(adapter);

    }
      //内部类适配器
    class MyAdapter extends ArrayAdapter<Data> {
        public MyAdapter(Context context, int resource, List<Data> objects) {
            super(context, resource, objects);
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (null == convertView) {
                convertView =getLayoutInflater()
                        .inflate(R.layout.list_item, null);
            }
            Data data=getItem(position);

            TextView dataText = (TextView)convertView.findViewById(R.id.text);
            dataText.setText(data.getDataText());
            ImageView dataImage = (ImageView)convertView.findViewById(R.id.image);
            dataImage.setImageResource (data.getDataImage());

            return convertView;

        }
    }

    //初始化数据
    public void  initData(){
        dataList=new ArrayList<Data>();
        dataList.add(new Data("apple",R.drawable.apple));
        dataList.add(new Data("banana",R.drawable.banana));
        dataList.add(new Data("orange",R.drawable.orange));
        dataList.add(new Data("watermelon",R.drawable.watermelon));

    }


    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

Data.java

package com.example.listviewdemo;

public class Data {
   private String dataText;
   private int dataImage;

    public Data(String dataText, int dataImage) {
        this.dataText = dataText;
        this.dataImage = dataImage;
    }

    public String getDataText() {
        return dataText;
    }

    public void setDataText(String dataText) {
        this.dataText = dataText;
    }

    public int getDataImage() {
        return dataImage;
    }

    public void setDataImage(int dataImage) {
        this.dataImage = dataImage;
    }
}