最常用和最难用的控件——ListView

ListView允许用户通过手指上下滑动的方式将屏幕外的数据滚动到屏幕内，同时屏幕上原有的数据也会滚动出屏幕

新建ListViewTest项目 

在activity_main.xml中添加如下代码定义ViewList控件

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

修改MainActivity中代码如下

public class MainActivity extends Activity {
 
    private String[] data = {"Apple", "Banana", "Orange", "Watermelon",
            "Pear", "Grape", "Pineapple", "Strawberry", "Cherry",
            "Apple", "Banana", "Orange", "Watermelon",
            "Pear", "Grape", "Pineapple", "Strawberry", "Cherry"};
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ArrayAdapter<String> adapter = new ArrayAdapter<String>(
                MainActivity.this, android.R.layout.simple_list_item_1,data);
        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }
}

3.5.2 定制ListView的界面

首先准备好一组图片分别对应每一种水果

接着定义一个实体类 作为L istView适配器 新建类Fruit代码如下

package com.example.listviewtest;
 
/**
 * Created by 孙伟 on 2016/3/18.
 */
public class Fruit {
    private String name;
 
    private int imageId;
 
    public Fruit (String name, int imageId) {
        this.name = name;
        this.imageId = imageId;
    }
    public String getName() {
        return name;
    }
 
    public int getImageId(){
        return imageId;
    }
}
 
 

Fruit类中只有两个字符 name表示水果名字，imageId表示水果对应图片的资源id

<?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:id="@+id/fruit_image"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
 
    <TextView
        android:id="@+id/fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginLeft="10dip"/>
</LinearLayout>

接下来创建一个自定义的适配器 这个适配器继承自ArrayAdapter 并将泛型指定为Fruit类。新建类FruitAdapter

package com.example.listviewtest;
 
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;
 
import java.util.List;
 
/**
 * Created by 孙伟 on 2016/3/18.
 */
public class FruitAdapter extends ArrayAdapter<Fruit> {
 
    private int resourceId;
 
    public FruitAdapter(Context context, int textViewResourceId,
                        List<Fruit> objects) {
        super(context, textViewResourceId, objects);
        resourceId = textViewResourceId;
    }
 
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Fruit fruit = getItem(position);//获取当前项的Fruit实例
        View view;
        if (convertView == null) {
            view = LayoutInflater.from(getContext()).inflate(resourceId,null);
        } else {
            view = convertView;
        }
        ImageView fruitImage = (ImageView) view.findViewById(R.id.fruit_image);
        TextView fruitName = (TextView) view.findViewById(R.id.fruit_name);
        fruitImage.setImageResource(fruit.getImageId());
        fruitName.setText(fruit.getName());
        return view;
 
    }
}

最后在MainActivity中修改为

package com.example.listviewtest;
 
import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
 
import java.util.ArrayList;
import java.util.List;
 
public class MainActivity extends Activity {
 
    private List<Fruit> fruitList = new ArrayList<Fruit>();
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initFruits();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,
                R.layout.fruit_item_activity,fruitList);
        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
    }
 
    private void initFruits() {
        Fruit apple = new Fruit("Apple", R.drawable.apple_pic);
        fruitList.add(apple);
        Fruit banana = new Fruit("Banana", R.drawable.banana_pic);
        fruitList.add(banana);
        Fruit orange = new Fruit("Orange", R.drawable.orange_pic);
        fruitList.add(orange);
        Fruit watermelon = new Fruit("Watermelon", R.drawable.watermelon_pic);
        fruitList.add(watermelon);
        Fruit pear = new Fruit("Pear", R.drawable.pear_pic);
        fruitList.add(pear);
        Fruit grape = new Fruit("Grape", R.drawable.grape_pic);
        fruitList.add(grape);
        Fruit pineapple = new Fruit("Pineapple", R.drawable.pineapple_pic);
        fruitList.add(pineapple);
        Fruit strawberry = new Fruit("Strawberry", R.drawable.strawberry_pic);
        fruitList.add(strawberry);
        Fruit cherry = new Fruit("Cherry", R.drawable.cherry_pic);
        fruitList.add(cherry);
        Fruit mango = new Fruit("Mango", R.drawable.mango_pic);
        fruitList.add(mango);
    }
 
}

3.5.3 提升ListView效率