依据url路径获取图片并显示到ListView中

项目开发中我们需要从网络获取图片显示到控件中，很多开源框架如Picasso可以实现图片下载和缓存功能。这里介绍的是一种简易的网络图片获取方式并把它显示到ListView中。

本案例实现的效果如下：

项目结构：

根据部分开源代码，我修改并封装了一个网络图片加载的工具类GetImageByUrl，通过调用其中的setImage方法，传入待显示图片的ImageView控件和该图片的url路径这两个参数即可实现获取网络图片的功能。

GetImageByUrl.java

package com.leo.imagelistview.util;

import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;

import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Handler;
import android.os.Message;
import android.widget.ImageView;

/**
 * 根据图片url路径获取图片
 * 
 * @author LeoLeoHan
 * 
 */
public class GetImageByUrl {

    private PicHandler pic_hdl;
    private ImageView imgView;
    private String url;


    /**
     * 通过图片url路径获取图片并显示到对应控件上
     * 
     * @param imgView
     * @param url
     */
    public void setImage(ImageView imgView, String url) {
        this.url = url;
        this.imgView = imgView;
        pic_hdl = new PicHandler();
        Thread t = new LoadPicThread();
        t.start();
    }


    class LoadPicThread extends Thread {
        @Override
        public void run() {
            Bitmap img = getUrlImage(url);
            System.out.println(img + "---");
            Message msg = pic_hdl.obtainMessage();
            msg.what = 0;
            msg.obj = img;
            pic_hdl.sendMessage(msg);
        }
    }

    class PicHandler extends Handler {

        @Override
        public void handleMessage(Message msg) {
            Bitmap myimg = (Bitmap) msg.obj;
            imgView.setImageBitmap(myimg);
        }

    }

    public Bitmap getUrlImage(String url) {
        Bitmap img = null;
        try {
            URL picurl = new URL(url);
            HttpURLConnection conn = (HttpURLConnection) picurl
                    .openConnection();
            conn.setConnectTimeout(6000);
            conn.setDoInput(true);
            conn.setUseCaches(false);
            conn.connect();
            InputStream is = conn.getInputStream();
            img = BitmapFactory.decodeStream(is);
            is.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return img;
    }
}

下面的代码就是实现ListView显示网络图片。
首先创建一个自定义的布局文件images_item.xml和自定义的ImageAdapter。

images_item.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" >

    <ImageView
        android:id="@+id/iv_image"
        android:layout_width="80dp"
        android:layout_height="80dp" />

    <LinearLayout
        android:layout_width="0dp"
        android:layout_height="80dp"
        android:layout_weight="1"
        android:orientation="vertical" >

        <TextView
            android:id="@+id/tv_url"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginTop="5dp"
            android:textSize="15sp" />
    </LinearLayout>

</LinearLayout>

ImageAdapter.java

package com.leo.imagelistview.adapter;

import java.util.List;
import java.util.Map;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;

import com.leo.imagelistview.R;
import com.leo.imagelistview.util.GetImageByUrl;

/**
 * 
 * @author LeoLeoHan
 * 
 */
public class ImageAdapter extends BaseAdapter {
    // 要显示的数据的集合
    private List<Map<String, Object>> data;
    // 接受上下文
    private Context context;
    // 声明内部类对象
    private ViewHolder viewHolder;

    /**
     * 构造函数
     * 
     * @param context
     * @param data
     */
    public ImageAdapter(Context context, List<Map<String, Object>> data) {
        this.context = context;
        this.data = data;
    }

    // 返回的总个数
    @Override
    public int getCount() {
        // TODO Auto-generated method stub
        return data.size();
    }

    // 返回每个条目对应的数据
    @Override
    public Object getItem(int position) {
        // TODO Auto-generated method stub
        return data.get(position);
    }

    // 返回的id
    @Override
    public long getItemId(int position) {
        // TODO Auto-generated method stub
        return position;
    }

    // 返回这个条目对应的控件对象
    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // 判断当前条目是否为null
        if (convertView == null) {
            viewHolder = new ViewHolder();
            convertView = View.inflate(context, R.layout.images_item, null);
            viewHolder.iv_image = (ImageView) convertView
                    .findViewById(R.id.iv_image);
            viewHolder.tv_url = (TextView) convertView
                    .findViewById(R.id.tv_url);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        // 获取List集合中的map对象
        Map<String, Object> map = data.get(position);
        // 获取图片的url路径
        String url = map.get("url").toString();
        // 这里调用了图片加载工具类的setImage方法将图片直接显示到控件上
        GetImageByUrl getImageByUrl = new GetImageByUrl();
        getImageByUrl.setImage(viewHolder.iv_image, url);
        viewHolder.tv_url.setText(url);

        return convertView;
    }

    /**
     * 内部类 记录单个条目中所有属性
     * 
     * @author LeoLeoHan
     * 
     */
    class ViewHolder {
        public ImageView iv_image;
        public TextView tv_url;
    }

}

MainActivity.java

package com.leo.imagelistview;

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

import com.leo.imagelistview.adapter.ImageAdapter;

import android.app.Activity;
import android.os.Bundle;
import android.widget.BaseAdapter;
import android.widget.ListView;

public class MainActivity extends Activity {

    private List<Map<String, Object>> data = new ArrayList<Map<String, Object>>();
    //声明控件
    private ListView lv_images;

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

        // 获取ListView对象
        lv_images = (ListView) findViewById(R.id.lv_images);
        //获取数据
        getData();
        BaseAdapter adapter = new ImageAdapter(this, data);
        //设置适配器
        lv_images.setAdapter(adapter);

    }

    /**
     * 简单添加一些网络图片的url路径
     * 实际开发中url路径是从服务器中解析json数据
     */
    public void getData() {
        String url1 = "http://my.csdn.net/uploads/avatar/6/A/7/1_leoleohan.jpg";
        String url2 = "http://img1.cache.netease.com/men/2014/6/2/2014060213070843617.jpg";
        String url3 = "http://static2.businessinsider.com/image/522f7a076da811e1404b39a9-480-/jony-ive-9.png";
        String url4 = "http://y0.ifengimg.com/8e16f14474b61551/2013/0731/rdn_51f878236017c.jpg";

        Map<String, Object> map1 = new HashMap<String, Object>();
        map1.put("url", url1); 

        Map<String, Object> map2 = new HashMap<String, Object>();
        map2.put("url", url2);

        Map<String, Object> map3 = new HashMap<String, Object>();
        map3.put("url", url3);

        Map<String, Object> map4 = new HashMap<String, Object>();
        map4.put("url", url4);

        data.add(map1);
        data.add(map2);
        data.add(map3);
        data.add(map4);
    }
}

activity_main.xml

<RelativeLayout 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="${relativePackage}.${activityClass}" >

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

</RelativeLayout>