安卓 Adapter 使用详解

￡神魔★判官ぃ 2022-03-27 09:52 326阅读 0赞

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);
      }
    }