Android笔记（二十一） Android中的Adapter

         Android中有一些View是包含多个元素的，例如ListView，GridView等，为了给View的每一个元素都设置数据，就需要Adapter了。

         常用的Adapter包括ArrayAdapter和SimpleAdapter。

ArrayAdapter

         ArrayAdapter比较简单，它只能用于显示文字。看代码：

MainActivity.java

package cn.lixyz.listviewtest;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemClickListener{

    private ListView listView;

    private String[] data = {"橘子","苹果","香蕉","西瓜","樱桃","猕猴桃","木瓜","山竹",
            "桃","葡萄","山楂","杏","核桃","哈密瓜","菠萝","柚子","无花果","柠檬","李子"};

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

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(MainActivity.this, android.R.layout.simple_list_item_1, data);

        listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(adapter);
        listView.setOnItemClickListener(this);
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        String text = listView.getItemAtPosition(position) + "";
        Toast.makeText(this,"position=" + position + " text=" + text,Toast.LENGTH_SHORT).show();

        Intent intent = new Intent(MainActivity.this,ShowFruit.class);
        intent.putExtra("fruitNum",position);
        startActivity(intent);
    }
}

activity_layout.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >

    </ListView>

</LinearLayout>

ShowFruit.java

package cn.lixyz.listviewtest;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.TextView;

public class ShowFruit extends AppCompatActivity {


    private String[] data = {"橘子橘子橘子橘子橘子", "苹果苹果苹果苹果苹果", "香蕉香蕉香蕉香蕉香蕉",
            "西瓜西瓜西瓜西瓜西瓜", "樱桃樱桃樱桃樱桃樱桃", "猕猴桃猕猴桃猕猴桃猕猴桃猕猴桃",
            "木瓜木瓜木瓜木瓜木瓜", "山竹山竹山竹山竹山竹", "桃桃桃桃桃", "葡萄葡萄葡萄葡萄葡萄",
            "山楂山楂山楂山楂山楂", "杏杏杏杏杏", "核桃核桃核桃核桃核桃", "哈密瓜哈密瓜哈密瓜哈密瓜哈密瓜",
            "菠萝菠萝菠萝菠萝菠萝", "柚子柚子柚子柚子柚子", "无花果无花果无花果无花果无花果",
            "柠檬柠檬柠檬柠檬柠檬", "李子李子李子李子李子"};

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


        int i = getIntent().getIntExtra("fruitNum", -1);
        ((TextView) findViewById(R.id.tv_fruit_desc)).setText(data[i]);

        findViewById(R.id.bt_back).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });
    }
}

activity_show_fruit.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cn.lixyz.listviewtest.ShowFruit"
    android:orientation="vertical">

    <TextView
        android:id="@+id/tv_fruit_desc"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textSize="60sp"/>

    <Button
        android:id="@+id/bt_back"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="返回"/>
</LinearLayout>

         运行结果：

Simpleadapter

         名字叫simple其实并不simple，它可以帮助我们实现更复杂的界面，ListView的大部分应用场景，都可以通过SimpleAdapter来提供列表项。

         如图：

实现代码：

MainActivity.java

package cn.lixyz.listviewtest;

import android.content.Context;
import android.content.Intent;
import android.graphics.Bitmap;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.SimpleAdapter;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

public class MainActivity extends AppCompatActivity implements AdapterView.OnItemClickListener {

    private ListView listView;

    private String[] data = {"橘子", "苹果", "香蕉", "西瓜", "樱桃", "猕猴桃", "木瓜", "山竹",
            "桃", "葡萄", "山楂", "杏", "核桃", "哈密瓜", "菠萝", "柚子", "无花果", "柠檬", "李子"};

    private List<Map<String, Object>> dataList;

    private String[] from = {"iv_fruit_show", "tv_fruit_name"};
    private int[] to = {R.id.iv_fruit_show, R.id.tv_fruit_name};


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

        listView = (ListView) findViewById(R.id.list_view);
        dataList = new ArrayList<Map<String, Object>>();
        SimpleAdapter sa = new SimpleAdapter(MainActivity.this, getData(), R.layout.layout_adapter, from, to);

        listView.setAdapter(sa);

        listView.setOnItemClickListener(this);
    }


    private List<Map<String, Object>> getData() {


        List<Integer> list = new ArrayList<Integer>();
        for (int i = 0; i < 18; i++) {
            list.add(getIdByName(MainActivity.this, "drawable", "pic" + i));
        }


        for (int i = 0; i < 18; i++) {
            Map<String, Object> map = new HashMap<String, Object>();
            map.put("iv_fruit_show", list.get(i));
            map.put("tv_fruit_name", data[i]);
            dataList.add(map);
        }
        return dataList;
    }


    public static int getIdByName(Context context, String className, String resName) {
        String packageName = context.getPackageName();
        int indentify = context.getResources().getIdentifier(resName, className, packageName);
        return indentify;
    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Intent intent = new Intent(MainActivity.this, ShowFruit.class);
        intent.putExtra("index", position);
        startActivity(intent);
    }
}

activity_layout.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <ListView
        android:id="@+id/list_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >

    </ListView>

</LinearLayout>

ShowFruit.java

package cn.lixyz.listviewtest;

import android.content.Context;
import android.media.Image;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;

import static cn.lixyz.listviewtest.R.drawable.pic0;

public class ShowFruit extends AppCompatActivity {


    private String[] data = {"橘子橘子橘子橘子橘子", "苹果苹果苹果苹果苹果", "香蕉香蕉香蕉香蕉香蕉",
            "西瓜西瓜西瓜西瓜西瓜", "樱桃樱桃樱桃樱桃樱桃", "猕猴桃猕猴桃猕猴桃猕猴桃猕猴桃",
            "木瓜木瓜木瓜木瓜木瓜", "山竹山竹山竹山竹山竹", "桃桃桃桃桃", "葡萄葡萄葡萄葡萄葡萄",
            "山楂山楂山楂山楂山楂", "杏杏杏杏杏", "核桃核桃核桃核桃核桃", "哈密瓜哈密瓜哈密瓜哈密瓜哈密瓜",
            "菠萝菠萝菠萝菠萝菠萝", "柚子柚子柚子柚子柚子", "无花果无花果无花果无花果无花果",
            "柠檬柠檬柠檬柠檬柠檬", "李子李子李子李子李子"};

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


        int i = getIntent().getIntExtra("index", -1);
        int picId = getIdByName(this, "drawable", "pic" + i);

        ((ImageView) findViewById(R.id.iv_fruit_show)).setImageResource(picId);
        ((TextView) findViewById(R.id.tv_fruit_desc)).setText(data[i]);

    }

    public static int getIdByName(Context context, String className, String resName) {
        String packageName = context.getPackageName();
        int indentify = context.getResources().getIdentifier(resName, className, packageName);
        return indentify;
    }
}

activity_show_fruit.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="cn.lixyz.listviewtest.ShowFruit"
    android:orientation="vertical">

    <ImageView
        android:id="@+id/iv_fruit_show"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        />

    <TextView
        android:id="@+id/tv_fruit_desc"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

layout_adapter.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:orientation="horizontal"
    android:weightSum="1">

    <ImageView
        android:id="@+id/iv_fruit_show"
        android:layout_width="80dp"
        android:layout_height="match_parent"
        android:layout_marginLeft="10dp"
        android:src="@drawable/pic0"/>

    <TextView
        android:id="@+id/tv_fruit_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="1111"
        android:textSize="50dp" />


</LinearLayout>

　　

         查看API，发现SimpleAdapter可以将静态数据映射到xml文件定义好的视图中去，你可以指定数据支持的列表如ArrayList组成的Map，在ArrayList中的每个条目对应List中的一行，Maps包含每行数据，你可以指定一个定义了被用于显示行的视图XML文件，通过关键字映射到指定的视图。绑定数据到视图分为两个阶段，首先，如果一个SimpleAdapter.ViewBinder是有效的，setViewValue(android.View.view,Object,String)将被调用。如果返回值是真，绑定成功，如果返回值为假，下面的视图将按照以下顺去去处理：

• l  一个实现了Checkable的视图（例如CheckBox），期望绑定值是一个布尔类型。
• l  TextView期望绑定值是一个字符串类型，通过调用setViewText(TextView, String)绑定。
• l  ImageView期望绑定值是一个资源id或者一个字符串，通过调用setViewImage(ImageView, int) 或 setViewImage(ImageView, String)。

　　如果没有一个合适的绑定发生将会抛出IllegalStateException

SimpleAdapter的构造函数

         public SimpleAdapter(Context context, List<?extends Map<String,?>> data, int resource, String[] from, int[] to)

参数：

         context：关联SimpleAdapter运行着的视图的上下文

         data：一个Map列表，在列表中的每个条目对应列表中的一行，应该包含所有在from指定的条目

         resource：一个定义列表项目视图布局的资源唯一表示。布局文件将至少应包含哪些定义在to中定义了的名称

         from：一个将被添加到Map上关联每一个项目的列名称的列表

         to：应该在参数from显示列的视图，这些应该全是TextView。在列表中最初的N视图是从参数from中最初的N列获取的值