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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
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:
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);
}
}
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<T>, BaseAdapter, CursorAdapter, HeaderViewListAdapter, ListAdapter, ResourceCursorAdapter, SimpleAdapter, SimpleCursorAdapter, SpinnerAdapter, WrapperListAdapter.我猜想这些Adapter的区别在于你的数据来源不一样：比如若你的数据来源于一个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等。就目前我经常使用的BaseAdapter和SimpleCursorAdapter。
1，BaseAdapter:---数据来源于Arraylist-->MyArraylist
当你继承BaseAdapter客制化你的Adapter时，你必须OverWrite以下函数：
Java代码
@Override
public int getCount() {
// TODO Auto-generated method stub
System.out.println("the size is\t" + MyArraylist.size());
return MyArraylist.size();
}
@Override
public int getCount() {
// TODO Auto-generated method stub
System.out.println("the size is\t" + MyArraylist.size());
return MyArraylist.size();
}
getCount返回的就是你的有多少条数据需要绑定的，也就是需要多少个View.比如这里返回的就是MyArraylist的Size.
Java代码
public View getView(int position, View v, ViewGroup parent) {
// TODO Auto-generated method stub
View view;
if (v == null) {
view = mInflater.inflate(R.layout.track_list_item, null);
} else {
view = v;
}}
public View getView(int position, View v, ViewGroup parent) {
// TODO Auto-generated method stub
View view;
if (v == null) {
view = mInflater.inflate(R.layout.track_list_item, null);
} else {
view = v;
}}
通过getView就获得了view来显示数据了。在这里你就可以自定义你的View了，但你通过XML定义可以通过LayoutInflater来inflater你的XML。getView里面就可以将MyArraylist的数据通过position 这个来将数据一条绑定一个View了。
2,SimpleCursorAdapter：---数据来源于数据库--->MyCursor
要实现bindView()和newView()这两个抽象方法需要实现的内容。
public void bindView(View view, Context context, Cursor cursor)，重用一个已有的view，使其显示当前cursor所指向的数据。
public View newView(Context context, Cursor cursor, ViewGroup parent)，为cursor所指向的数据新建一个View对象，并显示其数据。
通俗的说：比如你一个listview在一个屏幕里一次只能显示8条数据，那么第一次显示的时候就会newView 8次生成8个View,调用bindView绑定8条数据，而你有16条数据，但你拖动滚动条看9-16条时，此时不会再调用newView了，而只能调用了bindView去绑定新的数据而了。这样就省了空间了。
注意：传入到CursorAdapter中的Cursor结果集必须包含有列名为_id的列，否则SimpleCursorAdapter将不会起作用。
对于SimpleCursorAdapter中的newView与bindView的作用在BaseAdapter中的getView中也有这样的意义：getView里面我们必须做判断才能达到这种效果，就是要判断第二个参数View的是否为空：当空时就Infalte新的View，但不为空时就要就用它，这样就第一屏幕Infate 8个View，后面就直接使用这个8个view了。
注意：getView中是返回一个view，必须返回的是你infalte之后不为空的View，不然会报空指针异常
