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

<!--main.xml-->
<?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

<!--stationitem.xml-->
<?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<String> linesAdapter;
        private List<String> 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<SubwayLine> listLines = subwayService.getLineScrollData();
    linesNames = new ArrayList<String>();
    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<String>(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<SubwayStation> stations = subwayService.getStationLineScrollData(line.getLineId());
            /*把stations的属性值放到List<HashMap<String, String>>中*/
            List<HashMap<String, String>> data = new    ArrayList<HashMap<String, String>>();
                        for (SubwayStation station : stations) {
                          HashMap<String, String> map = new HashMap<String, String>();
                          if(station.getIsChange() == 1){
                            map.put("stationName", station.getStationName());
                            List<SubwayStation> 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<Weather> weatherList;        //这就是adapter关联的List，用来存储数据．还记的ArrayList

        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 );
        }

}

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<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 );
        }
}

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

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<Integer, View> m = new HashMap<Integer, View>();

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);
  }
}

出处http://lichen.blog.51cto.com/697816/492200