Android中Adapter接口及其实现类详解
16lz
2021-01-23
一、Adapter简单介绍：
（1）Android官方文档这样介绍： An Adapter object acts as a bridge between an AdapterView and the underlying data for that view. The Adapter provides access to the data items. The Adapter is also responsible for making a View for each item in the data set.
（2）Adapter接口及实现类
先来一张图，了解一下Adapter实现类的继承关系：
Adapter本身只是一个接口，它派生了SpinnerAdapter和ListAdapter两个子接口，其中ListAdapter为AbsListView提供列表项，而SpinnerAdapter为AbsSpinner提供列表项。由于ListView和GridView两个控件都继承AbsListView,所以ListAdapter其实是为ListView和GridView提供列表项。当然，Spinner和Gallery两个控件都继承AbsSpinner,所以SpinnerAdapter其实是为Spinner和Gallery提供列表项。控件的继承关系如下图：
BaseAdapter同时实现了SpinnerAdapter和ListAdapter两个接口。几乎所有Adapter都继承了BaseAdapter，因此，BaseAdapter及其子类可以同时为AbsListView、AbsSpinner提供列表项。 二、Adapter常用的实现类如下：
1. BaseAdapter:是一个抽象类，继承它需要实现较多的方法，所以灵活性和扩展性比较好。 class MyAdapter extends BaseAdapter{ private List> mList = null;//要显示的数据 /** * 得到数据集合中数据项数 * @return 集合中数据的项数 */ @Override public int getCount() { return mList.size(); } /** * 返回指定位置的数据项 * @param i 指定的位置 * @return */ @Override public Object getItem(int i) { return mList.get(i); } /** * 返回指定位置数据项的ID * @param i * @return */ @Override public long getItemId(int i) { return i; } //为每一个数据项产生相应的视图 @Override public View getView(int i, View view, ViewGroup viewGroup) { return null; } //----以上方法是必须实现的，下面两个方法是非必须实现的。 //当一个ListView的列表项有多种布局的情况下，需要实现这两个方法。 //根据数据源的position返回需要显示的布局的类型 @Override public int getItemViewType(int position) { return super.getItemViewType(position); } //返回所有布局的数量 @Override public int getViewTypeCount() { return super.getViewTypeCount(); } } ListView ls= (ListView) this.findViewById(R.id.listView); //列表项的数据 String[] strs={"JAVA","C#","JAVA Web","Android"}; //适配器 ArrayAdapter adapter=new ArrayAdapter(this,R.layout.support_simple_spinner_dropdown_item,strs); //把数据填充到ListView中 ls.setAdapter(adapter); ListView ls= (ListView) this.findViewById(R.id.listView); //列表项的数据 List list=new ArrayList(); list.add("JAVA"); list.add("C#"); list.add("JAVA Web"); list.add("Android"); //适配器 ArrayAdapter adapter=new ArrayAdapter(this,R.layout.support_simple_spinner_dropdown_item,list); //把数据填充到ListView中 ls.setAdapter(adapter); /** * Constructor * * @param context The context where the View associated with this SimpleAdapter is running * @param data A List of Maps. Each entry in the List corresponds to one row in the list. The * Maps contain the data for each row, and should include all the entries specified in * "from" * @param resource Resource identifier of a view layout that defines the views for this list * item. The layout file should include at least those named views defined in "to" * @param from A list of column names that will be added to the Map associated with each * item. * @param to The views that should display column in the "from" parameter. These should all be * TextViews. The first N views in this list are given the values of the first N columns * in the from parameter. */ public SimpleAdapter(Context context, List<? extends Map> data, @LayoutRes int resource, String[] from, @IdRes int[] to) { mData = data; mResource = mDropDownResource = resource; mFrom = from; mTo = to; mInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE); } <?xml version="1.0" encoding="utf-8"?> <?xml version="1.0" encoding="utf-8"?> package com.example.adapter;import android.app.Activity;import android.os.Bundle;import android.widget.ListView;import android.widget.SimpleAdapter;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;public class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); String[] name = {"小强", "小红", "小芳"}; String[] motto = {"好记性不如烂笔头", "好好学习，天天向上", "一寸光阴一寸金"}; int[] imageId = new int[]{R.drawable.e, R.drawable.g, R.drawable.l}; //创建一个List集合，List集合的元素是Map List> list = new ArrayList>(); for (int i = 0; i < name.length; i++) { Map map = new HashMap(); map.put("header", imageId[i]); map.put("name", name[i]); map.put("motto", motto[i]); list.add(map); } //在布局文件中找到ListView ListView ls = (ListView) this.findViewById(R.id.listView); //创建适配器Adapter SimpleAdapter simpleAdapter = new SimpleAdapter(this, list, R.layout.simple_item, new String[]{"header", "name", "motto"}, new int[]{R.id.head, R.id.name, R.id.motto}); //为ListView设置Adapter ls.setAdapter(simpleAdapter); }} 
4.SimpleCursorAdapter:这个Adapter是Android专门为了连接数据库与视图而产生的。先看一下Android源码中SimpleCursorAdapter的构造函数：
/** * Standard constructor. * * @param context The context where the ListView associated with this * SimpleListItemFactory is running * @param layout resource identifier of a layout file that defines the views * for this list item. The layout file should include at least * those named views defined in "to" * @param c The database cursor. Can be null if the cursor is not available yet. * @param from A list of column names representing the data to bind to the UI. Can be null * if the cursor is not available yet. * @param to The views that should display column in the "from" parameter. * These should all be TextViews. The first N views in this list * are given the values of the first N columns in the from * parameter. Can be null if the cursor is not available yet. * @param flags Flags used to determine the behavior of the adapter, * as per {@link CursorAdapter#CursorAdapter(Context, Cursor, int)}. */ public SimpleCursorAdapter(Context context, int layout, Cursor c, String[] from, int[] to, int flags) { super(context, layout, c, flags); mTo = to; mOriginalFrom = from; findColumns(c, from); }更多相关文章
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