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ListView与适配器
ListView是什么
ListView是一个以垂直方式在项目中显示视图的列表(即在一个窗口里可以滚动查看数据,比如说查看聊天记录),是一种不能实现确定视图中的内容的适配器视图(adapter view)。数据和视图的绑定,需要通过继承ListViewAdapter接口的适配器实现。确保当上下滚动的时候,能够动态刷新视图内容。通常我们都会自定义一个继承自BaseAdapter(已继承ListViewAdapter)或ArrayAdapter(继承自BaseAdapter)又或者SimpleAdapter(继承自BaseAdapter)的类,并重写getView()方法,实现自己想要的功能。
适配器是什么
适配器是一个连接数据和AdapterView(ListView就是一个典型的AdapterView,还有RecyclerView等等)的桥梁,通过它能有效地实现数据与AdapterView的分离设置,使AdapterView与数据的绑定更加简便,修改更加方便。简单地来说就是把一些数据弄得适当,以便于在View上显示。
常用的适配器:
//1.BaseAdapter//BaseAdapter是最基本的适配器。它实际上就是一个抽象类,它有四种抽象方法public int getCount() 得到Item的总数public Object getItem(int position) 根据position得到某个Item的对象public long getItemId (int position) 根据position得到某个ItemIdpublic View getView(int position, View convertView, ViewGroup parent) //得到相应position对应的Item视图,position当前Item的位置,convertView复用的View对象//2.ArrayAdapter//ArrayAdapter是BaseAdapter的子类,与SimpleAdapter相同,ArrayAdapter也不是抽象类,与下面的SimpleA的用法类似,开发者要在构造方法里传入相应的参数即可适配数据,尝适配于TextView。public ArrayAdapter(Context context,int resource,int textViewResourceId,T[] objects//需要适配的数据数组);//3.SimpleAdapter//SimpleAdapter继承自BaseAdapter,实现了BaseAdapter的四个抽象方法。开发者需要在创建SimpleAdapter实例时,在构造方法里传入相应的参数即可。要注意的是SimpleAdapter只能适配于Checkable,TextView,ImageView,其中Checkable是一个接口,CheckBox控件就实现了该接口。public SimpleAdapter(Context context,List<? extends Map<String, ?>>data,int resource,String[] from,int[] to);
1.BaseAdapter
子项布局
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_height="fill_parent"android:layout_width="fill_parent"> <Buttonandroid:layout_alignParentRight="true" android:layout_width="wrap_content"android:layout_height="wrap_content" android:id="@+id/ItemButton"android:text="按钮"android:focusable="false"/> <TextView android:id="@+id/ItemTitles" android:layout_height="wrap_content" android:layout_width="fill_parent" android:textSize="20sp"/><TextViewandroid:id="@+id/ItemTexts" android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_below="@+id/ItemTitles"/>
</RelativeLayout>
MainActivity
public class ListViewBaseAdapter extends Activity {private ListView lv;/*定义一个动态数组*/ ArrayList<HashMap<String, Object>> listItem;@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_list_view_base_adapter);lv = (ListView) findViewById(R.id.base_lv);MyAdapter mAdapter = new MyAdapter(this);//得到一个MyAdapter对象lv.setAdapter(mAdapter);//为ListView绑定Adapter /*为ListView添加点击事件*/ lv.setOnItemClickListener(new OnItemClickListener() {@Overridepublic void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3) {Log.v("MyListViewBase", "你点击了ListView条目" + arg2);//在LogCat中输出信息}});}/*添加一个得到数据的方法,方便使用*/ private ArrayList<HashMap<String, Object>> getDate(){ArrayList<HashMap<String, Object>> listItem = new ArrayList<HashMap<String,Object>>();/*为动态数组添加数据*/ for(int i=0;i<30;i++) { HashMap<String, Object> map = new HashMap<String, Object>(); map.put("ItemTitle", "第"+i+"行"); map.put("ItemText", "这是第"+i+"行"); listItem.add(map); } return listItem;}/* * 新建一个类继承BaseAdapter,实现视图与数据的绑定*/ private class MyAdapter extends BaseAdapter {private LayoutInflater mInflater;//得到一个LayoutInfalter对象用来导入布局 /*构造函数*/ public MyAdapter(Context context) {this.mInflater = LayoutInflater.from(context);}@Overridepublic int getCount() {return getDate().size();//返回数组的长度 }@Overridepublic Object getItem(int position) {return null;}@Overridepublic long getItemId(int position) {return 0;}/*书中详细解释该方法*/ @Overridepublic View getView(final int position, View convertView, ViewGroup parent) {ViewHolder holder;//观察convertView随ListView滚动情况 Log.v("MyListViewBase", "getView " + position + " " + convertView);if (convertView == null) {convertView = mInflater.inflate(R.layout.base_adapter_item,null);holder = new ViewHolder();/*得到各个控件的对象*/ holder.title = (TextView) convertView.findViewById(R.id.ItemTitles);holder.text = (TextView) convertView.findViewById(R.id.ItemTexts);holder.bt = (Button) convertView.findViewById(R.id.ItemButton);convertView.setTag(holder);//绑定ViewHolder对象 }else{holder = (ViewHolder)convertView.getTag();//取出ViewHolder对象 }/*设置TextView显示的内容,即我们存放在动态数组中的数据*/ holder.title.setText(getDate().get(position).get("ItemTitle").toString());holder.text.setText(getDate().get(position).get("ItemText").toString());/*为Button添加点击事件*/ holder.bt.setOnClickListener(new OnClickListener() {@Overridepublic void onClick(View v) {Log.v("MyListViewBase", "你点击了按钮" + position);//打印Button的点击信息}}); return convertView;}}/*存放控件*/ public final class ViewHolder{public TextView title;public TextView text;public Button bt;}
}
2.ArrayAdapter
新建类Fruit,作为ListView适配器的适配类型
package com.example.listviewtest;public class Fruit {private String name;private int imageId;public Fruit(String name, int imageId) {this.name = name;this.imageId = imageId;}public String getName() {return name;}public int getImageId() {return imageId;}}
为ListView的子项指定一个我们自定义的布局,在layout目录下新建fruit_item.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="horizontal"android:layout_width="match_parent"android:layout_height="match_parent"><ImageViewandroid:id="@+id/fruit_image"android:layout_width="wrap_content"android:layout_height="wrap_content" /><TextViewandroid:id="@+id/fruit_name"android:layout_width="wrap_content"android:layout_height="wrap_content"android:layout_gravity="center_vertical"android:layout_marginLeft="10dp" /></LinearLayout>
创建一个自定义的适配器FruitAdapter
public class FruitAdapter extends ArrayAdapter<Fruit> {private int resourceId;//重写父类的构造函数//将上下文、ListView子项布局的id和数据都传递进来public FruitAdapter(Context context, int textViewResourceId,List<Fruit> objects) {super(context, textViewResourceId, objects);resourceId = textViewResourceId;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// 获取当前项的Fruit实例Fruit fruit = getItem(position); //LayoutInflater.from(this); 获取LayoutInflater实例//使用LayoutInflater为子项加载我们传入的布局//inflate的三个参数:要转换的xml布局、给加载好的布局再添加一个父布局、//是否让父布局的layout属性失效View view = LayoutInflater.from(getContext()).inflate(resourceId, parent, false);TextView fruitName = view.findViewById(R.id.fruit_name);ImageView fruitImage = view.findViewById(R.id.fruit_image);fruitName.setText(fruit.getFruitName());fruitImage.setImageResource(fruit.getImageId());return view;
}
修改MainActivity
public class MainActivity extends AppCompatActivity {private List<Fruit> fruitList = new ArrayList<>();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//初始化水果数据initFruits();FruitAdapter adapter = new FruitAdapter(MainActivity.this, R.layout.fruit_item,fruitList);ListView listView = (ListView) findViewById(R.id.list_view);listView.setAdapter(adapter);}private void initFruits() {//初始化水果数据的操作:比如/*Fruit apple = new Fruit("Apple", R.drawable.apple_pic);*fruitList.add(apple);*Fruit banana = new Fruit("Banana", R.drawable.banana_pic);*fruitList.add(banana);*/
}
3.SimpleAdapter
simple_adapter_item.xml
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_height="fill_parent"android:layout_width="fill_parent"> <ImageViewandroid:layout_alignParentRight="true" android:layout_width="wrap_content"android:layout_height="wrap_content" android:id="@+id/ItemImage"/> <TextView android:id="@+id/ItemTitle" android:layout_height="wrap_content" android:layout_width="fill_parent" android:textSize="20sp"/><TextViewandroid:id="@+id/ItemText" android:layout_height="wrap_content" android:layout_width="fill_parent" android:layout_below="@+id/ItemTitle"/>
</RelativeLayout>
MainActivity
private ListView lv;@Override
public void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_list_view_simple_adapter);lv = (ListView) findViewById(R.id.lv2);/*定义一个动态数组*/ ArrayList<HashMap<String, Object>> listItem = new ArrayList <HashMap<String,Object>>();/*在数组中存放数据*/for(int i=0;i<10;i++) { HashMap<String, Object> map = new HashMap<String, Object>(); map.put("ItemImage", R.drawable.ic_launcher);//加入图片 map.put("ItemTitle", "第"+i+"行"); map.put("ItemText", "这是第"+i+"行"); listItem.add(map); }//new String 数据来源, new int 数据到哪去SimpleAdapter mSimpleAdapter = new SimpleAdapter(this,listItem,R.layout.simple_adapter_item,new String[] {"ItemImage","ItemTitle", "ItemText"}, new int[] {R.id.ItemImage,R.id.ItemTitle,R.id.ItemText});lv.setAdapter(mSimpleAdapter);//为ListView绑定适配器 lv.setOnItemClickListener(new OnItemClickListener() {@Overridepublic void onItemClick(AdapterView<?> arg0, View arg1, int arg2,long arg3) {setTitle("你点击了第"+arg2+"行");//设置标题栏显示点击的行 }});
}