Android 开发笔记___基本适配器的使用__BaseAdapter

之前用到过ArryAdapter适用于纯文本的列表数据，SimpleAdapter适用于带图标的列表数据，但在实际应用中常常有更复杂的列表，比如同一项中存在多个控件，这时候用前面的两个会比较复杂，而且不易扩展。因此Android提供了适应性更强的BaseAdapter，该适配器允许开发者在别的代码文件中进行逻辑处理，大大提高了代码的可读性、可维护性。

从BaseAdapter派生的数据适配器主要实现下面三个方法：

• 构造函数：指定适配器需要处理的数据集合。
• getCount：获取数据项的个数。
• getView：获取每项的展示视图，并对每项的内部空间进行业务处理

下面以spinner为载体演示如何操作BaseAdapter：

　　一、编写列表项的布局文件

 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:id="@+id/ll_item"
     android:layout_width="match_parent"
     android:layout_height="wrap_content"
     android:orientation="horizontal" >

     <ImageView
         android:id="@+id/iv_icon"
         android:layout_width="0dp"
         android:layout_height="80dp"
         android:layout_weight="1"
         android:scaleType="fitCenter" />

     <LinearLayout
         android:layout_width="0dp"
         android:layout_height="match_parent"
         android:layout_weight="3"
         android:orientation="vertical" >

         <TextView
             android:id="@+id/tv_name"
             android:layout_width="match_parent"
             android:layout_height="0dp"
             android:layout_weight="1"
             android:gravity="left|center"
             android:textColor="@color/black"
             android:textSize="20sp" />

         <TextView
             android:id="@+id/tv_desc"
             android:layout_width="match_parent"
             android:layout_height="0dp"
             android:layout_weight="2"
             android:gravity="left|center"
             android:textColor="@color/black"
             android:textSize="13sp" />
     </LinearLayout>

 </LinearLayout>

　　二、写个新的适配器继承BaseAdapter：

 package com.example.alimjan.hello_world.adapter;

 import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.AdapterView;
 import android.widget.AdapterView.OnItemClickListener;
 import android.widget.AdapterView.OnItemLongClickListener;
 import android.widget.BaseAdapter;
 import android.widget.ImageView;
 import android.widget.LinearLayout;
 import android.widget.TextView;
 import android.widget.Toast;

 import com.example.alimjan.hello_world.bean.planet;
 import com.example.alimjan.hello_world.R;

 import java.util.ArrayList;

 public class PlanetAdapter extends BaseAdapter implements OnItemClickListener,
         OnItemLongClickListener {

     private LayoutInflater mInflater;
     private Context mContext;
     private int mLayoutId;
     private ArrayList<planet> mPlanetList;
     private int mBackground;

     public PlanetAdapter(Context context, int layout_id, ArrayList<planet> planet_list, int background) {
         mInflater = LayoutInflater.from(context);
         mContext = context;
         mLayoutId = layout_id;
         mPlanetList = planet_list;
         mBackground = background;
     }

     @Override
     public int getCount() {
         return mPlanetList.size();
     }

     @Override
     public Object getItem(int arg0) {
         return mPlanetList.get(arg0);
     }

     @Override
     public long getItemId(int arg0) {
         return arg0;
     }

     @Override
     public View getView(final int position, View convertView, ViewGroup parent) {
         ViewHolder holder = null;
         if (convertView == null) {
             holder = new ViewHolder();
             convertView = mInflater.inflate(mLayoutId, null);
             holder.ll_item = (LinearLayout) convertView.findViewById(R.id.ll_item);
             holder.iv_icon = (ImageView) convertView.findViewById(R.id.iv_icon);
             holder.tv_name = (TextView) convertView.findViewById(R.id.tv_name);
             holder.tv_desc = (TextView) convertView.findViewById(R.id.tv_desc);
             convertView.setTag(holder);
         } else {
             holder = (ViewHolder) convertView.getTag();
         }
         planet planet = mPlanetList.get(position);
         holder.ll_item.setBackgroundColor(mBackground);
         holder.iv_icon.setImageResource(planet.image);
         holder.tv_name.setText(planet.name);
         holder.tv_desc.setText(planet.desc);
         return convertView;
     }

     public final class ViewHolder {
         private LinearLayout ll_item;
         public ImageView iv_icon;
         public TextView tv_name;
         public TextView tv_desc;
     }

     @Override
     public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
         String desc = String.format("您点击了第%d个行星，它的名字是%s", position + 1,
                 mPlanetList.get(position).name);
         Toast.makeText(mContext, desc, Toast.LENGTH_LONG).show();
     }

     @Override
     public boolean onItemLongClick(AdapterView<?> parent, View view, int position, long id) {
         String desc = String.format("您长按了第%d个行星，它的名字是%s", position + 1,
                 mPlanetList.get(position).name);
         Toast.makeText(mContext, desc, Toast.LENGTH_LONG).show();
         return true;
     }
 }

　　三、在页面代码中构造该适配器，，并应用于spinner对象：

 package com.example.alimjan.hello_world;

 import java.util.ArrayList;

 /**
  * Created by alimjan on 7/16/2017.
  */

         import com.example.alimjan.hello_world.adapter.PlanetAdapter;
         import com.example.alimjan.hello_world.bean.planet;
         import android.content.Context;
         import android.content.Intent;
         import android.graphics.Color;
         import android.os.Bundle;
         import android.support.v7.app.AppCompatActivity;
         import android.view.View;
         import android.widget.AdapterView;
         import android.widget.Spinner;
         import android.widget.Toast;
         import android.widget.AdapterView.OnItemSelectedListener;

 public class class_5_2_1 extends AppCompatActivity {

     private ArrayList<planet> planetList;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.code_5_2_1);
         initSpinner();
     }

     private void initSpinner() {
         planetList = planet.getDefaultList();
         PlanetAdapter adapter = new PlanetAdapter(this, R.layout.item_list, planetList, Color.WHITE);
         Spinner sp = (Spinner) findViewById(R.id.sp_planet);
         sp.setPrompt("请选择行星");
         sp.setAdapter(adapter);
         sp.setSelection(0);
         sp.setOnItemSelectedListener(new MySelectedListener());
     }

     private class MySelectedListener implements OnItemSelectedListener {
         public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
             Toast.makeText(class_5_2_1.this, "您选择的是"+planetList.get(arg2).name, Toast.LENGTH_LONG).show();
         }

         public void onNothingSelected(AdapterView<?> arg0) {
         }
     }

     public static void startHome(Context mContext) {
         Intent intent = new Intent(mContext, class_5_2_1.class);
         mContext.startActivity(intent);
     }

 }

plenet 类在这

 package com.example.alimjan.hello_world.bean;

 import java.util.ArrayList;
 import com.example.alimjan.hello_world.R;

 /**
  * Created by alimjan on 7/16/2017.
  */

 public class planet {
     public int image;
     public String name;
     public String desc;

     public planet() {
         this.image = 0;
         this.name = "";
         this.desc = "";
     }

     public planet(int image, String name, String desc) {
         this.image = image;
         this.name = name;
         this.desc = desc;
     }

     private static int[] iconArray = {R.drawable.shuixing, R.drawable.jinxing, R.drawable.diqiu,
             R.drawable.huoxing, R.drawable.muxing, R.drawable.tuxing};
     private static String[] nameArray = {"水星", "金星", "地球", "火星", "木星", "土星"};
     private static String[] descArray = {
             "水星是太阳系八大行星最内侧也是最小的一颗行星，也是离太阳最近的行星",
             "金星是太阳系八大行星之一，排行第二，距离太阳0.725天文单位",
             "地球是太阳系八大行星之一，排行第三，也是太阳系中直径、质量和密度最大的类地行星，距离太阳1.5亿公里",
             "火星是太阳系八大行星之一，排行第四，属于类地行星，直径约为地球的53%",
             "木星是太阳系八大行星中体积最大、自转最快的行星，排行第五。它的质量为太阳的千分之一，但为太阳系中其它七大行星质量总和的2.5倍",
             "土星为太阳系八大行星之一，排行第六，体积仅次于木星"
     };
     public static ArrayList<planet> getDefaultList() {
         ArrayList<planet> planetList = new ArrayList<planet>();
         for (int i=0; i<iconArray.length; i++) {
             planetList.add(new planet(iconArray[i], nameArray[i], descArray[i]));
         }
         return planetList;
     }
 }