关于SimpleAdapter的用法

ArrayAdapter主要用于每行列表只显示文本的情况，而SimpleAdapter则还可以给列表加上图标，允许在列表项中展示多个控件。

 下面以下拉框Sipnner为例，说明SimpleAdapter的用法。

layout文件夹里的activity_spinner.xml

<?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="15dp"
    android:orientation="vertical">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="请选择："
        android:textSize="26sp"
        android:gravity="center"
        android:paddingBottom="10dp"/>

    <Spinner
        android:id="@+id/sp_icon"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:spinnerMode="dialog" />"

</LinearLayout>

对应的SpinnerActivity类

package com.example.myapplication;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.SimpleAdapter;
import android.widget.Spinner;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class SpinnerActivity extends AppCompatActivity {

    //iconArray是行星的图标数组，starArray是行星的名称数组
    private int[] iconArray = {R.drawable.shuixing, R.drawable.jinxing, R.drawable.diqiu,
            R.drawable.huoxing, R.drawable.muxing, R.drawable.tuxing};
    private String[] starArray = {"水星", "金星", "地球", "火星", "木星", "土星"};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_spinner);
        //声明一个映像对象的队列，用于保存行星的图标与名称配对信息
        List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
        for (int i = 0; i < iconArray.length; i++) {
            Map<String, Object> item = new HashMap<String, Object>();
            item.put("icon", iconArray[i]);
            item.put("name", starArray[i]);
            list.add(item);
        }
        //声明一个下拉列表的简单适配器，其中制定了图标与文本两组数据
        SimpleAdapter starAdapter = new SimpleAdapter(this, list,
                R.layout.item_select, new String[] { "icon", "name" },
                new int[] {R.id.iv_icon, R.id.tv_name});
        //设置简单适配器的布局样式
        starAdapter.setDropDownViewResource(R.layout.item_simple);
        //从布局文件中获取名叫sp_icon的下拉框
        Spinner sp = (Spinner) findViewById(R.id.sp_icon);
        //设置下拉框的标题
        sp.setPrompt("请选择行星");
        //设置下拉框的简单适配器
        sp.setAdapter(starAdapter);
        //设置下拉框默认显示的第一项
        sp.setSelection(0);
        //给下拉框设置选择监听器，一旦用户选中某一项，就触发监听器的onItemSelected方法
        sp.setOnItemSelectedListener(new MySelectedListener());
    }


    class MySelectedListener implements AdapterView.OnItemSelectedListener {
        public void onItemSelected(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
            Toast.makeText(SpinnerActivity.this, "您选择的是"+starArray[arg2], Toast.LENGTH_SHORT).show();
        }

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

 layout文件夹里的item_select.xml和item_simple.xml。分别用于设置选中item的样式和下拉框的样式。

<TextView xmlns:android="http://schemas.android.com/apk/res/android" 
    android:id="@+id/tv_name"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:singleLine="true"
    android:gravity="center"
    android:textSize="17sp"
    android:textColor="#0000ff" />

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    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="50dp"
        android:layout_weight="1"
        android:gravity="center" />
    
    <TextView
        android:id="@+id/tv_name"
        android:layout_width="0dp"
        android:layout_height="match_parent"
        android:layout_weight="3"
        android:gravity="center"
        android:textSize="17sp"
        android:textColor="#ff0000" />

</LinearLayout>

 

---

在此分析一下SimpleAdapter的源码

public class SimpleAdapter extends BaseAdapter implements Filterable, ThemedSpinnerAdapter{
    private final LayoutInflater mInflater;

    private int[] mTo;
    private String[] mFrom;
    private ViewBinder mViewBinder;

    @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 115609023)
    private List<? extends Map<String, ?>> mData;

    private int mResource;
    private int mDropDownResource;

    /** Layout inflater used for {@link #getDropDownView(int, View, ViewGroup)}. */
    private LayoutInflater mDropDownInflater;

    private SimpleFilter mFilter;
    private ArrayList<Map<String, ?>> mUnfilteredData;

    public SimpleAdapter(Context context, List<? extends Map<String, ?>> 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);
    }

        .............

     public void setDropDownViewResource(int resource) {
        mDropDownResource = resource;
     }
        .............
}

可以看出，SimpleAdapter类继承了BaseAdapter抽象类，实现了Filterable和ThemedSpinnerAdapter接口。而BaseAdapter类又实现了ListAdapter和SpinnerAdapter接口。

关于该类的构造方法，一共有五个参数。

/**
 * 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.
 */

context:上下文；

data：需要展示的数据源，是map组成的list集合，每个Map对应ListView中的一行，每一个Map（键——值对）中的键名必须包含在from中所指定的键；

resource：展示的布局文件，可以自己在layout设置xml文件去设置需要展示 的样式；

from：Map中的键名；

to：绑定数据视图的ID，与from成对应的关系。
 

第二个参数是关于Map集合的List集合。定义为List<Map<String,Object>>。

new了一个starAdapter对象之后，便可以进行简单适配器的布局样式的设置。以及对下拉框的各种属性进行设置。

注意：setSelection方法要在setAdapter方法后调用。

运行效果如下：

 

 

 

资料来源：Android Studio开发实战