关于Android Adapter（适配器），参考Devin Zhang’s blog。简单的说，Adapter起到的作用是使得前端的显示和后端的数据能够适配，用以下代码作为例子
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public class MainActivity extends Activity{
private List<fruit> myFruits = new ArrayList<fruit>();//将数据定义为实例
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
initialFruits();
setContentView(R.layout.activity_main);//与R.layout.activity_main布局绑定
ListView lv = (ListView) findViewById(R.id.lv);
fruitAdapter adapter = new fruitAdapter(MainActivity.this,R.layout.list_item,myFruits);//fruitAdpter的三个参数依次为，上下文context,ListView单项布局文件，集合类型的数据
lv.setAdapter(adapter);//用adapter做适配器（就理解为ListView看得懂并且存放有数据的容器）
}
//初始化实例变量myFruits
private void initialFruits(){
fruit orange = new fruit("orange",R.drawable.pa);
myFruits.add(orange);
fruit grape = new fruit("grape",R.drawable.pb);
myFruits.add(grape);
fruit milk = new fruit("milk",R.drawable.pc);
myFruits.add(milk);
fruit bean = new fruit("bean",R.drawable.pd);
myFruits.add(bean);
fruit kid = new fruit("kid",R.drawable.pe);
myFruits.add(kid);
fruit banana = new fruit("banana",R.drawable.pf);
myFruits.add(banana);
fruit lamp = new fruit("lamp",R.drawable.pg);
myFruits.add(lamp);
fruit hack = new fruit("hack",R.drawable.ph);
myFruits.add(hack);
fruit keyboard = new fruit("keyboard",R.drawable.pi);
myFruits.add(keyboard);
fruit water = new fruit("water",R.drawable.pj);
myFruits.add(water);
fruit mouse = new fruit("mouse",R.drawable.pk);
myFruits.add(mouse);
fruit ear = new fruit("ear",R.drawable.pl);
myFruits.add(ear);
}
}
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关于fruitAdapter类
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public class fruitAdapter extends ArrayAdapter<fruit>{
private int resourceId;
//textViewResourceId即为传入的ListView的单项布局文件id
public fruitAdapter(Context context,int textViewResourceId, List<fruit> objects) {
super(context, textViewResourceId, objects);
//adapter对象的resourceId实例变量保存ListView的单项布局文件id，以供getView()使用
resourceId = textViewResourceId;
}
//在每个子项被滚动到屏幕内的时候调用getView()
@Override
public View getView(int position, View convertView, ViewGroup parent) {
fruit newFruit = getItem(position);
View view = LayoutInflater.from(getContext()).inflate(resourceId,null);
ImageView imageView = (ImageView) view.findViewById(R.id.fruit_image);
TextView textView = (TextView) view.findViewById(R.id.fruit_name);
imageView.setImageResource(newFruit.getId());
textView.setText(newFruit.getName());
return view;
}
}
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对于getView(),《第一行代码》中给出的解释是“在每个子项被滚动到屏幕内的时候会被调用”。这句话的另一层意思是：凡是ListView中可见的子项，均调用了getView()方法。事实上也只能如此，因为在构造函数中并未告诉ListView如何呈现样式。也因此呢，整个ListView的过程是：创建Adapter(需调用构造函数)->特定的ListView指定该Adapter->在屏幕需要显示子项时调用getView()
接着附上fruit类的代码
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public class fruit {
private String name;
private int pic_id;
public fruit(String fname,int id){
this.name = fname;
this.pic_id = id;
}
public String getName(){
return name;
}
public int getId(){
return pic_id;
}
}
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最后就出现了这样的ListView
界面
界面
这样看来图片的大小得事先选好，图片越大，速度越慢
滑动的时候确实会卡顿，优化如下:
getView()的convertView用于缓存加载好的布局，不至于每次有子项滑入屏幕内都要加载一次布局
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//在每个子项被滚动到屏幕内的时候调用getView()
@Override
public View getView(int position, View convertView, ViewGroup parent) {
View view;
ViewHolder viewHolder;
fruit myFruit = getItem(position);
if(convertView == null){
viewHolder = new ViewHolder();
view = LayoutInflater.from(getContext()).inflate(resourceId,null);
viewHolder.imageView = (ImageView) view.findViewById(R.id.fruit_image);
viewHolder.textView = (TextView) view.findViewById(R.id.fruit_name);
view.setTag(viewHolder);
}
else{
view = convertView;
viewHolder = (ViewHolder) view.getTag();
}
viewHolder.imageView.setImageResource(myFruit.getId());
viewHolder.textView.setText(myFruit.getName());
return view;
}
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从优化ListView过程中，看出至始至终都是使用第一次加载好的view，索性在view里面再加上存有控件实例的viewHolder
写子项->适配器->item->mainActivity(传数据)
