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.
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