Android Adapter

Adapter是用来帮助填充数据的中间桥梁，比如通过它将数据填充到ListView, GridView, Gallery.而android 提供了几种Adapter:ArrayAdapter, BaseAdapter, CursorAdapter, HeaderViewListAdapter, ListAdapter, ResourceCursorAdapter, SimpleAdapter, SimpleCursorAdapter, SpinnerAdapter, WrapperListAdapter.

根据数据来源形式的不同可以选择不同的Adapter,比如数据来源于一个Arraylist 就使用BaseAdapter,SimpleAdapter,而数据来源于通过查询数据库获得Cursor那就使用SimpleCursorAdapter.

使用simpleadapter的例子:

主布局文件

xml version ="1.0" encoding ="utf-8" ?>
< LinearLayout xmlns:android ="http://schemas.android.com/apk/res/android"
         android:orientation ="vertical"
         android:layout_width ="fill_parent"
         android:layout_height ="fill_parent"
         >
         < RelativeLayout
       android:layout_width ="wrap_content"
       android:layout_height ="wrap_content"
         >
         < Spinner
                 android:id ="@+id/subway_lines"
                 android:layout_width ="fill_parent"
                 android:layout_height ="wrap_content" >
         Spinner >
         < TextView
             android:layout_width ="fill_parent"
             android:layout_height ="wrap_content"
             android:layout_below ="@id/subway_lines"
             android:layout_alignLeft ="@id/subway_lines"
             android:id ="@+id/select_line"
         />
     RelativeLayout >
     < ListView
     android:layout_width ="fill_parent"
     android:layout_height ="fill_parent"
     android:id ="@+id/station_listView"
     />
LinearLayout >

然后是ListView布局

xml version ="1.0" encoding ="utf-8" ?>
< RelativeLayout
     xmlns:android ="http://schemas.android.com/apk/res/android"
     android:layout_width ="fill_parent"
     android:layout_height ="fill_parent" >
     < TextView
         android:layout_width ="200px"
         android:layout_height ="fill_parent"
         android:textSize ="20px"
         android:gravity ="center_horizontal"
         android:id ="@+id/station_name"
     />
     < TextView
         android:layout_width ="200px"
         android:layout_height ="fill_parent"
         android:layout_toRightOf ="@id/station_name"
         android:textSize ="20px"
         android:layout_alignTop ="@id/station_name"
         android:id ="@+id/station_info"
     />
RelativeLayout >

接下来是Activity

import java.util.ArrayList;

public class SubwayActivity extends Activity {

         private static final String TAG = "SubwayActivity";
         private SubwayService subwayService;
         private TextView selectLine;
         private Spinner subwayLines;
         private ArrayAdapter linesAdapter;
         private List linesNames;
         private ListView stationListView;
         private SimpleAdapter stationsAdapter;

        @Override
         public void onCreate(Bundle savedInstanceState) {
                 super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    stationListView = (ListView) findViewById(R.id.station_listView);
    subwayService = new SubwayService( this);

     //初始化数据
//    subwayService.init();

    List listLines = subwayService.getLineScrollData();
    linesNames = new ArrayList();
     for (SubwayLine subwayLine : listLines) {
      linesNames.add(subwayLine.getLineName());
    }
     // 第一步：添加一个下拉列表项的list，这里添加的项就是下拉列表的菜单项
    selectLine = (TextView) findViewById(R.id.select_line);
    subwayLines = (Spinner) findViewById(R.id.subway_lines);
     // 第二步：为下拉列表定义一个适配器，这里就用到里前面定义的list。
    linesAdapter = new ArrayAdapter( this, android.R.layout.simple_spinner_item,linesNames);
     // 第三步：为适配器设置下拉列表下拉时的菜单样式。
    linesAdapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
     // 第四步：将适配器添加到下拉列表上
    subwayLines.setAdapter(linesAdapter);
     //第五步：为下拉列表设置各种事件的响应，这个事响应菜单被选中
    subwayLines.setOnItemSelectedListener(selectedListener);
     /*下拉菜单弹出的内容选项触屏事件处理*/
    subwayLines.setOnTouchListener(onTouchListener);
     /*下拉菜单弹出的内容选项焦点改变事件处理*/
    subwayLines.setOnFocusChangeListener(onFocusChangeListener);
        }

         /**
         * 为下拉列表设置各种事件的响应，这个事响应菜单被选中
         */
         private OnItemSelectedListener selectedListener =     new Spinner.OnItemSelectedListener(){
          @SuppressWarnings( "unchecked")
                 public void onItemSelected(AdapterView arg0, View arg1, int arg2, long arg3) {
            String lineName = linesAdapter.getItem(arg2);
            SubwayLine line = subwayService.findLine(lineName);
             /*根据lineId查询出stations*/
            List stations = subwayService.getStationLineScrollData(line.getLineId());
             /*把stations的属性值放到List>中*/
            List> data = new    ArrayList>();
                         for (SubwayStation station : stations) {
                          HashMap map = new HashMap();
                           if(station.getIsChange() == 1){
                            map.put( "stationName", station.getStationName());
                            List changeStations = subwayService.getChangeStationExceptThis(station.getStationName(), line.getLineId());
                            StringBuilder builder = new StringBuilder();
                            builder.append( "换乘 ");
                             if(changeStations != null && changeStations.size() > 0){
                               for (SubwayStation changeStation : changeStations) {
                                SubwayLine changeLine = subwayService.findLine(changeStation.getLineId());
                                      builder.append(changeLine.getLineName()).append( ",");
                  }
                              builder.deleteCharAt(builder.length()-1);
                            }
                                  map.put( "stationInfo",builder.toString());
                          } else{
                            map.put( "stationName", station.getStationName());
                                  map.put( "stationInfo", station.getStationInfo());
                          }
                                data.add(map);
            }
                         /*设置stationsAdapter适配器*/
      stationsAdapter = new SimpleAdapter(
          SubwayActivity. this,
          data,
          R.layout.stationitem,
           new String[] { "stationName", "stationInfo" },
           new int[] { R.id.station_name, R.id.station_info });
      stationListView.setAdapter(stationsAdapter);

                         /* 将所选mySpinner 的值带入myTextView 中*/
                  selectLine.setText( "以下是："+ lineName + " 车站列表...");
                         /* 将mySpinner 显示*/
                        arg0.setVisibility(View.VISIBLE);
                }
                @SuppressWarnings( "unchecked")
                 public void onNothingSelected(AdapterView arg0) {
                  selectLine.setText("");
                        arg0.setVisibility(View.VISIBLE);
                }
        };

         /**
         * 下拉菜单弹出的内容选项触屏事件处理
         */
         private OnTouchListener onTouchListener = new Spinner.OnTouchListener(){
                 public boolean onTouch(View v, MotionEvent event) {
                         /* 将mySpinner 隐藏，不隐藏也可以，看自己爱好*/
//                        v.setVisibility(View.INVISIBLE);
                         return false;
                }
        };

         /**
         * 下拉菜单弹出的内容选项焦点改变事件处理
         */
         private OnFocusChangeListener onFocusChangeListener = new Spinner.OnFocusChangeListener(){
     public void onFocusChange(View v, boolean hasFocus) {
      v.setVisibility(View.VISIBLE);
    }
  };
}

其中,核心的是

/*设置stationsAdapter适配器*/
            stationsAdapter = new SimpleAdapter(
                    SubwayActivity. this,
                    data,
                    R.layout.stationitem,
                     new String[] { "stationName", "stationInfo" },
                     new int[] { R.id.station_name, R.id.station_info });
            stationListView.setAdapter(stationsAdapter);

===========================================================

以上是简单的使用adapter的方法,一般情况下这样就够用了.接下来是自定义adapter.

继承BaseAdapter,重写四个方法.

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

         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 );
        }

}

自定义的View

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 );
                }
}

最后在Activity中使用

public class CustomAdapterActivity extends ListActivity
{
        @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 );
        }
}

===========================================================

再就是Adapter的优化,一个广为流传的 ViewHolder、ViewCache办法：

public View getView( int position, View convertView, ViewGroup parent) {

  ViewHolder holder;
   if (convertView == null) {
    holder = new ViewHolder();
    convertView = inflater.inflate(R.layout.topic_list, null);
    holder.title = (TextView) convertView.findViewById(R.id.title);
    convertView.setTag(holder);
  } else {
    holder = (ViewHolder) convertView.getTag();
  }
}

public class ViewHolder {
   public TextView getTitle() {
     if (title == null) {
      title = (TextView) baseView.findViewById(R.id.title);
    }
     return title;
  }
}

或者使用HashMap做缓存的方法:

HashMap m = new HashMap();

public View getView( int position, View view, ViewGroup parent) {

  View convertView = m.get(position);
   if (convertView != null) {
     return convertView;
  } else {
    convertView = inflater.inflate(R.layout.topic_list, null);
    TextView title = (TextView) convertView.findViewById(R.id.title);
    m.put(position, convertView);
  }
}