我在剛玩android 時候,對這個adapter很不理解,到底是什麼原理呢?適配器,哎,只知道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 有多少數據項,根據這個數據確定有多少item.
2 確定每個item里加載哪個View.
3 把View里加載要顯示的數據.
問提一個一個來解決.
第一個問題:
因爲adapter都要關聯一個list.有來存儲數據.list的項數就是Item的數目.我們在重載BaseAdapter 時候,都要實現這個函數
public int getCount() {
return weatherList.size();
}
哎,這個函數就是確定關聯條目的.
第二個問題:
哪來的view呢?當然我們自己創建的.重載BaseAdapter時候你要實現getView()這個函數,就是這個view.
第三個問題:
你自己創建的view.加載哪些數據你該知道的.呵呵.
張豪就喜歡看例子,這個小夥子技術,管理都很牛,得以他爲榜樣.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<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?自己創建的啊,如果創建呢?
public class WeatherAdapter extends BaseAdapter {
private Context context;
private List<Weather> weatherList;
這就是adapter關聯的List,用來存儲數據.還記的ArrayList 要往裏傳參數嗎?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 的獲取就多中多樣了,我們可以傳個LayoutID. 通過Inflater出來,也可以自己創建個,只要出來就行.
在這裏,我們自己創建個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,細緻的理解.
原創地址沒找着,不好意思,就沒貼了。