（1）ListView

通过此方法定义一个带图片且加载效率高的ListView(使用Viewholder)

定义一个实体类Fruit

<span style="font-size:18px;">public class Fruit {//作为adapter的数据适配类型  
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;  
}  
}  </span>

为 ListView 的子项指定一个我们自定义的布局

<span style="font-size:18px;">在 layout 目录下新建  
fruit_item.xml，代码如下所示：  
<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>  </span>

新建类 FruitAdapter

<pre name="code" class="java"><pre name="code" class="java">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 = LayoutInflater.from(getContext()).inflate(resourceId, null);  
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;  
}  
}  

修改 MainActivity 中的代码

[java] view plain copy print?
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(); // 初始化水果数据  
FruitAdapter adapter = new FruitAdapter(MainActivity.this, R.layout.fruit_item,  
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);  
}  
} 

ListView使用优化

1 对convertView进行判断防止每次调用getView方法的时候丢创建新的view

2 使用viewholder来缓冲item中的控件。

3 注意：listview在布局中。不能设置自适应，避免导致getview方法的重复调用。

@Override
public View getView(int position, View convertView, ViewGroup parent) {
Fruit fruit = getItem(position);
View view;
ViewHolder viewHolder;
if (convertView == null) {
view = LayoutInflater.from(getContext()).inflate(resourceId, null);
viewHolder = new ViewHolder();
viewHolder.fruitImage = (ImageView) view.findViewById (R.id.fruit_image);
viewHolder.fruitName = (TextView) view.findViewById (R.id.fruit_name);
view.setTag(viewHolder); // 将ViewHolder存储在View中
} else {
view = convertView;
viewHolder = (ViewHolder) view.getTag(); // 重新获取ViewHolder
}
viewHolder.fruitImage.setImageResource(fruit.getImageId());
viewHolder.fruitName.setText(fruit.getName());
return view;

}
class ViewHolder {
ImageView fruitImage;
TextView fruitName;
}

相关注释：

每一次为ListView设置内容都需要adapter 中getview方法返回一个view来提供显示。

getview中三个参数分别为 int position（显示view在listview中的位置）,

 View convertView（在recycle中的view）,

 ViewGroup parent（正在显示的view）

 getview方法中添加

System.out.println("看这里" + position +"    "+ convertView);

进行了解。

下图为GetView方法中参数图解：