（轉）android adapter的學習

我在剛玩android 時候，對這個adapter很不了解，到底是什麼原理呢？　擴充卡，哎，隻知道setAdapter()把參數傳進去，系統就顯示出來了。

今天，針對這個東西，我們做個系統詳細的分析．

listview加載adapter過程是這樣的．

１　先判斷adapter 有多少資料項，根據這個資料确定有多少item. 

２　确定每個item裡加載哪個View.　

３　把View裡加載要顯示的資料．

問提一個一個來解決．　第一個問題：　因為adapter都要關聯一個list .有來存儲資料．list的項數就是Item的數目．　我們在重載BaseAdapter 時候，都要實作這個函數

public int getCount() {                           

        return weatherList.size();   

    }   

哎，這個函數就是确定關聯條目的．

第二個問題　哪來的view 呢，　當然我們自己建立的．重載BaseAdapter時候你要實作getView()這個函數，就是這個view.

第三個問題，你自己建立的view.加載哪些資料你該知道的．呵呵．

張豪就喜歡看例子，這個小夥子技術，管理都很牛，得以他為榜樣．　得努力．

public class CustomAdapterActivity extends ListActivity   

{   

    @Override  

    public void onCreate(Bundle savedInstanceState)   

    {   

        super.onCreate(savedInstanceState);   

        setContentView(R.layout.main);   

        ArrayList<Weather> weatherList = new ArrayList<Weather>();   

        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，這個大家都很清楚，關鍵問題是weatherAdapter 哪來的呢？　自己建立的啊，如果建立呢？

public class WeatherAdapter extends BaseAdapter {   

    private Context context;   

    private List<Weather> weatherList;   　這就是adapter關聯的List，用來存儲資料．還記的ArrayList　要往裡傳參數嗎？　傳的也是這個類型啊．呵呵

    public WeatherAdapter(Context context, List<Weather> 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，這段告訴了我們，有多少個Item，　可以通過getCount()得到了。　可是View 哪來的呢？

當然是getView ()這個函數提供．

這個view 的擷取就多中多樣了，我們可以傳個LayoutID. 通過Inflater出來，也可以自己建立個，隻要出來就行．

在這裡，我們自己建立個View. 這個View.是個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 );   

        }   

}   

有了這個就很清楚了．　呵呵，很明白吧，　一定得深入，細緻的了解．

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