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ItemId
public 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">
<Button
android: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"/>
<TextView
android: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;
@Override
public 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() {
@Override
public 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);
}
@Override
public int getCount() {
return getDate().size();//返回数组的长度
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
/*书中详细解释该方法*/
@Override
public 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() {
@Override
public 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">
<ImageView
android:id="@+id/fruit_image"
android:layout_width="wrap_content"
android:layout_height="wrap_content" />
<TextView
android: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;
}
@Override
public 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<>();
@Override
protected 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">
<ImageView
android: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"/>
<TextView
android: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() {
@Override
public 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
}
});
}