基本适配器 BaseAdapter

新建一个activity，命名为 BaseAdapterActivity，这里以Spinner为载体，演示 BaseAdapter 的用法

public class BaseAdapterActivity extends AppCompatActivity {
    private ArrayList<Planet> planetList;

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

    private void initPlanetSpinner() {
        planetList = Planet.getDefaultList();
        PlanetListAdapter adapter = new PlanetListAdapter(this, planetList);
        Spinner sp = findViewById(R.id.sp_planet);
        sp.setPrompt("请选择行星");
        sp.setAdapter(adapter);
        sp.setOnItemSelectedListener(new MySelectedListener());
    }

    private class MySelectedListener implements AdapterView.OnItemSelectedListener {

        @Override
        public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
            ToastUtil.showToast(BaseAdapterActivity.this, "您选择的是" + planetList.get(position).name);
        }

        @Override
        public void onNothingSelected(AdapterView<?> parent) {

        }
    }
}

BaseAdapterActivity 对应的xml文件为：activity_base_adapter 如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="10dp"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:gravity="center"
        android:text="行星的列表视图"
        android:textColor="@color/black"
        android:textSize="20sp" />

    <Spinner
        android:id="@+id/sp_planet"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:spinnerMode="dialog" />

</LinearLayout>

编写新的适配器 PlanetListAdapter 继承于 BaseAdapter，实现对列表项的获取与操作，如下：

public class PlanetListAdapter extends BaseAdapter {
    private Context mContext;
    private ArrayList<Planet> mPlanetList;

    public PlanetListAdapter(Context context, ArrayList<Planet> arrayList) {
        mContext = context;
        mPlanetList = arrayList;
    }

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

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

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

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder holder;
        if (convertView == null) {
            holder = new ViewHolder();
            convertView = LayoutInflater.from(mContext).inflate(R.layout.item_list, null);
            holder.iv_icon = convertView.findViewById(R.id.iv_icon);
            holder.tv_name = convertView.findViewById(R.id.tv_name);
            holder.tv_desc = convertView.findViewById(R.id.tv_desc);
            convertView.setTag(holder); // 将视图持有者保存到转换视图中
        } else {
            holder = (ViewHolder)convertView.getTag();
        }
        Planet info = mPlanetList.get(position);
        holder.iv_icon.setImageResource(info.image);
        holder.tv_name.setText(info.name);
        holder.tv_desc.setText(info.desc);
        return convertView;
    }

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

PlanetListAdapter 中对应的布局文件为 item_list ，如下：

<?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:background="@color/white"
    android:paddingTop="10dp"
    android:paddingBottom="10dp"
    android:layout_height="100dp">

    <ImageView
        android:id="@+id/iv_icon"
        android:layout_marginLeft="5dp"
        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_marginLeft="5dp"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:textSize="20sp"
            android:textColor="@color/black" />

        <TextView
            android:id="@+id/tv_desc"
            android:layout_width="match_parent"
            android:layout_marginLeft="5dp"
            android:layout_marginRight="5dp"
            android:layout_height="0dp"
            android:layout_weight="2"
            android:textColor="@color/gray"
            android:textSize="13sp" />

    </LinearLayout>

</LinearLayout>

PlanetListAdapter 中对应的模型为Planet 如下：

public class Planet {
    public int image;
    public String name;
    public String 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 < nameArray.length; i++) {
            planetList.add(new Planet(iconArray[i], nameArray[i], descArray[i]));
        }
        return planetList;
    }
}

效果图如下

• 左边的图是BaseAdapterActivity的显示效果
• 右边的图是PlanetListAdapter的显示效果