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;
    }
}