Android 从网上下载图片并显示到ListView上

首先我们要准备好图片的数据，就是一些网站上图片的地址

拿到之后就可以直接来写了

package com.example.androidnet;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;

import android.app.Activity;
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;

public class ListViewShowPic extends Activity {

ListView listView;

@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.show_listview);

listView = (ListView) findViewById(R.id.lv_show_img);

MyAdapter adapter = new MyAdapter(this);
listView.setAdapter(adapter);
Log.d("logd", "--UI--");
}

class MyAdapter extends BaseAdapter {

/**
 * 网上的图片url
 */
String[] picUrls = new String[] {
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/3e1acdd6ecdf4dc2aa9abc45be2443db.jpg",
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/cff4bd31c3934c8388cd5b47d3d34e29.jpg",
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/4fd9f3557acd4fb28b28af7a89a2ff27.jpg",
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/7ead2966291e45c4aef8a198f127bd4a.jpg",
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/245c7655f4de4536a539a559c9434ce4.jpg",
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/51b047314ca74259839c4e6e666e9c71.jpg",
"http://bmob-cdn-1178.b0.upaiyun.com/2016/05/10/1a11e2a135bf4bc29fd60831c64f558c.jpg" };
/**
 * 名称对应url上的图片名称
 */
String[] picNames = new String[] {
"3e1acdd6ecdf4dc2aa9abc45be2443db.jpg",
"cff4bd31c3934c8388cd5b47d3d34e29.jpg",
"4fd9f3557acd4fb28b28af7a89a2ff27.jpg",
"7ead2966291e45c4aef8a198f127bd4a.jpg",
"245c7655f4de4536a539a559c9434ce4.jpg",
"51b047314ca74259839c4e6e666e9c71.jpg",
"1a11e2a135bf4bc29fd60831c64f558c.jpg" };
String path = Environment.getExternalStorageDirectory()
+ "/listviewImg/";// 文件目录

LayoutInflater layoutInflater;
Context context;
File fileDir;

public MyAdapter(Context context) {
this.context = context;
layoutInflater = (LayoutInflater) context
.getSystemService(Context.LAYOUT_INFLATER_SERVICE);


/**
 * 文件目录如果不存在，则创建
 */
fileDir = new File(path);
if (!fileDir.exists()) {
fileDir.mkdirs();
}

}

@Override
public int getCount() {
return picUrls.length;
}

@Override
public Object getItem(int position) {
return picUrls[position];
}

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

@Override
public View getView(int position, View convertView, ViewGroup parent) {

View view = layoutInflater.inflate(R.layout.listview_img, null);

ImageView imageView = (ImageView) view.findViewById(R.id.img);

/**
 * 创建图片文件
 */
File file = new File(fileDir, picNames[position]);
if (!file.exists()) {// 如果本地图片不存在则从网上下载
downloadPic(picNames[position], picUrls[position]);
} else {// 图片存在则填充到listview上
Bitmap bitmap = BitmapFactory
.decodeFile(file.getAbsolutePath());
imageView.setImageBitmap(bitmap);
}
return view;
}

/**
 * 使用子线程下载图片
 * 
 * @param name
 * @param url
 */
private void downloadPic(final String name, final String picurl) {

new Thread(new Runnable() {

@Override
public void run() {

FileOutputStream fos = null;
InputStream in = null;

// 创建文件
File file = new File(fileDir, name);

try {

fos = new FileOutputStream(file);

URL url = new URL(picurl);

in = url.openStream();

int len = -1;
byte[] b = new byte[1024];
while ((len = in.read(b)) != -1) {
fos.write(b, 0, len);
}

} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (fos != null) {
fos.close();
}
if (in != null) {
in.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}).start();

}

}
}

两个布局文件show_listview.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="vertical"
   >



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

    </ListView>
</LinearLayout>

listview_img.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:gravity="center"
    android:orientation="vertical" >

    <ImageView 
        android:id="@+id/img"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:src="@drawable/bgimg"/>

</LinearLayout>

配置权限

<!-- 在SDCard中创建与删除文件权限 -->
    <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS" />
    <!-- 往SDCard写入数据权限 -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.INTERNET" />

demo下载：http://download.csdn.net/detail/an_illusion/9516537