Android 学习之---listview adapter分析(一)

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．

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);
temperatureContr