android开发之ListView

MobSec

##ListView功能很强大，类似Windows下的列表菜单。
如下实现一个简单的ListView.

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

###通过内置的适配器进行界面关联

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListView;
public class MainActivity extends AppCompatActivity {
    private String[] data = {"apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango"};
    @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);
    }
}

其中ArrayAdapter的构造函数参数为:

  1. 上线文
  2. 子项布局ID
  3. 数据

加入图片

新建布局fruit_item.xml如下

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" 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_vertical"
        android:layout_marginLeft="10dp"/>
</LinearLayout>

用类来封装子项数据

class Fruit
{
    private String name;
    private  int imageId;
    public Fruit(String name,int imageId)
    {
        this.imageId = imageId;
        this.name = name;
    }
    public String getName()
    {
        return name;
    }
    public int getImageId()
    {
        return imageId;
    }
}

重新实现一个FruitAdapter

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);    //获取当前想的Fruit实例
        View view;                          // convertView 已加载view进行缓存
        ViewHolder viewHolder;
        if (convertView == null)
        {
            view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.fruitImage = (ImageView)view.findViewById(R.id.fruit_image);
            viewHolder.fruitName = (TextView)view.findViewById(R.id.fruit_name);
            view.setTag(viewHolder);
        }
        else
        {
            view = convertView;
            viewHolder = (ViewHolder)view.getTag(); //重新得到ViewHolder
        }
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
    }
    class ViewHolder
    {
        ImageView fruitImage;
        TextView fruitName;
    }
}

注意上面代码对ListView有两处优化，分别为：

  1. convertView 为上次缓存View，若不为空即可不用重新生成View
  2. 用ViewHolder将已经findViewById成功的控件保存起来,防止每次都在布局中找而耗时

最终入口代码如下:

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);    //获取当前想的Fruit实例
        View view;                          // convertView 已加载view进行缓存
        ViewHolder viewHolder;
        if (convertView == null)
        {
            view = LayoutInflater.from(getContext()).inflate(resourceId,parent,false);
            viewHolder = new ViewHolder();
            viewHolder.fruitImage = (ImageView)view.findViewById(R.id.fruit_image);
            viewHolder.fruitName = (TextView)view.findViewById(R.id.fruit_name);
            view.setTag(viewHolder);
        }
        else
        {
            view = convertView;
            viewHolder = (ViewHolder)view.getTag(); //重新得到ViewHolder
        }
        viewHolder.fruitImage.setImageResource(fruit.getImageId());
        viewHolder.fruitName.setText(fruit.getName());
        return view;
    }
    class ViewHolder
    {
        ImageView fruitImage;
        TextView fruitName;
    }
}

public class MainActivity extends AppCompatActivity {
    //private String[] data = {"apple","Banana","Orange","Watermelon","Pear","Grape","Pineapple","Strawberry","Cherry","Mango"};
    private List<Fruit> fruitList = new ArrayList<Fruit>();
    @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);
        */
        InitFruits();
        FruitAdapter adapter = new FruitAdapter(MainActivity.this,R.layout.fruit_item,fruitList);
        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Fruit fruit = fruitList.get(position);
                Toast.makeText(MainActivity.this,fruit.getName(),Toast.LENGTH_SHORT).show();
            }
        });
    }
    private void InitFruits()
    {
        for (int i = 0 ; i < 2 ; ++i)
        {
            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);
        }
    }
}