android adapter 深刻分析

我在刚玩android 时候，对这个adapter很不理解，到底是什么原理呢？　适配器，哎，只知道setAdapter()把参数传进去，系统就显示出来了。

今天，针对这个东西，我们做个系统详细的分析．

listview加载adapter过程是这样的．

１　先判断adapter 有多少数据项，根据这个数据确定有多少item.
２　确定每个item里加载哪个View.　
３　把View里加载要显示的数据．

问提一个一个来解决．　第一个问题：　因为adapter都要关联一个list .有来存储数据．list的项数就是Item的数目．　我们在重载BaseAdapter 时候，都要实现这个函数

public int getCount() {                          
        return weatherList.size();  
    }  

哎，这个函数就是确定关联条目的．

第二个问题　哪来的view 呢，　当然我们自己创建的．重载BaseAdapter时候你要实现getView()这个函数，就是这个view.

第三个问题，你自己创建的view.加载哪些数据你该知道的．呵呵．

张豪就喜欢看例子，这个小伙子技术，管理都很牛，得以他为榜样．　得努力．

public class CustomAdapterActivity extends ListActivity  
{  
    /** Called when the activity is first created. */  
    @Override  
    public void onCreate(Bundle savedInstanceState)  
    {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.main);  
        ArrayList weatherList = new ArrayList();  
        Weather w = new Weather( "London", 17, Weather.OVERCAST );  
        weatherList.add( w );  
        w = new Weather( "Paris", 22, Weather.OVERCAST );  
        weatherList.add( w );  
        w = new Weather( "Athens", 29, Weather.SUNNY );  
        weatherList.add( w );  
        w = new Weather( "Stockholm", 12, Weather.RAIN );  
        weatherList.add( w );  
        WeatherAdapter weatherAdapter = new WeatherAdapter(    
                this,  
                weatherList );    
        setListAdapter( weatherAdapter );  
    }  
}  

哎，这个大家都很清楚，关键问题是weatherAdapter 哪来的呢？　自己创建的啊，如果创建呢？

public class WeatherAdapter extends BaseAdapter {  
  
    private Context context;  
    private List weatherList;   　这就是adapter关联的List，用来存储数据．还记的ArrayList　要往里传参数吗？　传的也是这个类型啊．呵呵
  
    public WeatherAdapter(Context context, List weatherList ) {    
        this.context = context;  
        this.weatherList = weatherList;  
    }  
  
    public int getCount() {                          
        return weatherList.size();  
    }  
  
    public Object getItem(int position) {        
        return weatherList.get(position);  
    }  
  
    public long getItemId(int position) {    
        return position;  
    }  
  
    public View getView(int position, View convertView, ViewGroup parent) {    
        Weather weather = weatherList.get(position);  
        return new WeatherAdapterView(this.context, weather );  
    }  
  
}  

哎，这段告诉了我们，有多少个Item，　可以通过getCount()得到了。　可是View 哪来的呢？
当然是getView ()这个函数提供．

这个view 的获取就多中多样了，我们可以传个LayoutID. 通过Inflater出来，也可以自己创建个，只要出来就行．

在这里，我们自己创建个View. 这个View.是个VIewGroup.


class WeatherAdapterView extends LinearLayout {          
        public static final String LOG_TAG = "WeatherAdapterView";  
  
        public WeatherAdapterView(Context context,    
                                Weather weather ) {  
            super( context );  
  
            this.setOrientation(HORIZONTAL);          
            LinearLayout.LayoutParams cityParams =    
                new LinearLayout.LayoutParams(100, LayoutParams.WRAP_CONTENT);  
            cityParams.setMargins(1, 1, 1, 1);  
  
            TextView cityControl = new TextView( context );  
            cityControl.setText( weather.getCity() );  
            addView( cityControl, cityParams);          
  
            LinearLayout.LayoutParams temperatureParams =    
                new LinearLayout.LayoutParams(20, LayoutParams.WRAP_CONTENT);  
            temperatureParams.setMargins(1, 1, 1, 1);  
  
            TextView temperatureControl = new TextView(context);  
            temperatureControl.setText( Integer.toString( weather.temperature ) );  
            addView( temperatureControl, temperatureParams);              
  
            LinearLayout.LayoutParams skyParams =    
                new LinearLayout.LayoutParams(25, LayoutParams.WRAP_CONTENT);  
  
            ImageView skyControl = new ImageView( context );  
            Log.d( LOG_TAG, weather.getCity()+" -> "+weather.sky );  
            skyControl.setImageResource( weather.getSkyResource() );  
            addView( skyControl, skyParams );  
        }  
}  
  
有了这个就很清楚了．　呵呵，很明白吧，　一定得深入，细致的理解．