Android Adapter

Adapter接口派生了ListAdapter和SpinnerAdapter接口，ListAdapter为AbsListView提供列表项，SpinnerAdapter为AbsSpinner提供列表项，Adapter常用的实现类如下：

ArrayAdapter:将数组活列表中的多个值包装成列表项，每个列表项只能是TextView或者其子类

ArrayAdapter String []arr={"悟空","八戒","牛魔王"};
 //第二个参数必须是TextView或者其子类的资源Id
 ArrayAdapter<String> adapter=new ArrayAdapter<String>(this,R.layout.array_item,arr);
 ListView list=(ListView)findViewById(R.id.list);
 list.setAdapter(adapter);

SimpleAdapter:可将list集合中的多个对象包装成列表项,每个列表项对应一个Layout

SimpleAdapter    String []names=new String[]{"虎头","弄玉","李清照","李白"};
    String []descs=new String[]{"good boy","good girl","bad boy","bad girl"};
    List<Map<String,Object>>listItems=new ArrayList<Map<String,Object>>();
    for(int i=0;i<names.length;i++) {
            Map<String, Object> listItem = new HashMap<String, Object>();
            listItem.put("header",R.drawable.ic_launcher);
            listItem.put("personName", names[i]);
            listItem.put("desc", descs[i]);
            listItems.add(listItem);
        }
        //map的key与控件id对应
        SimpleAdapter simpleAdapter=new SimpleAdapter(this,listItems,R.layout.simple_item,new String[]{"header","personName","desc"},
                new int[]{R.id.header,R.id.name,R.id.desc});
        ListView list1=(ListView)findViewById(R.id.list1);
        list1.setAdapter(simpleAdapter);

SimpleCursorAdapter:用于包装Cursor提供的数据,其构造函数为

public SimpleAdapter(Context context,
             List<? extends Map<String,?>> data,
             int resource,
             String[] from,
             int[] to)

SimpleCursorAdapterString[] fromColumns = new String[] {People.NUMBER, People.NAME};
int[] toLayoutIDs = new int[] { R.id.nameTextView, R.id.numberTextView};
SimpleCursorAdapter myAdapter = new SimpleCursorAdapter(this,R.layout.simplecursorlayout,cursor,fromColumns,toLayoutIDs);
myListView.setAdapter(myAdapter);

BaseAdapter:常用来扩展，可以实现对列表项最大限度的定制.自定义BaseAdapter时要重写它的多个方法,比较重要的有getCount,getView方法.ListView设置了BaseAdapter，系统开始绘制ListView的时候,首先调用getCount方法得到ListView的item数目,然后调用getView逐条绘制item

View getView(int position,View convertView,ViewGroup parent):显示data set position位置的数据的view.其中convertView参数需要注意。它的工作原理是:以ListView为例，当初始显示时，每次显示一个item都调用一次getView方法，每次调用convertView都为空,当显示完后，如果屏幕移动了并且导致有些Item移出屏幕，此时如果还有新的item需要产生,调用getView时convertView参数就不为空，而是移出屏幕的item的view，所以为了提高效率可以重用之前的view,代码如下

BaseAdapter getView    @Override  
    public View getView(int position, View convertView, ViewGroup parent)  
    {  
        Cache cache;  
        if(null==convertView)  
        {  
            cache=new Cache();  
            convertView=LayoutInflater.from(mContext).inflate(R.layout.textview, null); 
            cache.textView=(TextView)convertView.findViewById(R.id.textview);  
            convertView.setTag(cache);  
        }  
        else  
        {  
            //复用old view
            cache=(Cache)convertView.getTag();  
        }  
        cache.textView.setText("position: "+position);  
         return convertView;           
    }  
   //用于缓存item的所有view，不用重复创建
    class Cache  
    {  
        public TextView textView;  

    }

继承关系如图所示：

posted on 2014-09-12 21:18 哨兵阅读(...) 评论(...) 编辑收藏