Android Adapter

冷不防 2022-01-15 13:23 223阅读 0赞

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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<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);  
  \}  
\}

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