android 异步更新imageview 图片

也许有很多人会遇到一个图片加载不出来的时候, 有这么一个现象,当你第一次可以加载到图片,但是到第二次就加载不出来了,这个问题主要原因是图片读取问题,我现在把我做的例子分享给大家,希望对大家有帮助...

main.xml布局文件文件

<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.cn" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:label="@string/app_name" android:name=".AsyncImageViewActivity" > <intent-filter > <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-permission android:name="android.permission.INTERNET" /> </manifest>

2,AsyncImageViewActivity类

package com.cn; import android.app.Activity; import android.os.Bundle; import android.widget.ImageView; public class AsyncImageViewActivity extends Activity { private ImageView user_image; //用户头像 @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); user_image = (ImageView)findViewById(R.id.user_image); String image_url = "http://fs.yy365.com/d3/photos/2010/05/20/09/pic_1274317680739_a637337f-0769-4cb3-ad07-bb2b1ba38c4a_1.jpg"; //异步加载头像 AsyncImageLoader.setImageViewFromUrl(image_url, user_image); } }

3,对于图片异步处理类:AsyncImageLoader ,这个类我采用了缓存.提高图片的访问效率,其中图片的读取方式被我修改了,只要不会出现图片读取出错的情况.

package com.cn; import java.io.BufferedInputStream; import java.io.ByteArrayInputStream; import java.io.ByteArrayOutputStream; import java.io.InputStream; import java.lang.ref.SoftReference; import java.net.URL; import java.util.HashMap; import android.graphics.drawable.Drawable; import android.os.Handler; import android.os.Message; import android.util.Log; import android.widget.ImageView; /** * 对于图片异步处理类 * @author liuxr * */ public class AsyncImageLoader { static ImageView singImageView; //针对于单张图片异步加载 private static HashMap<String, SoftReference<Drawable>> singleImageCache = null; /** * 通过图片地址,返回drawable * @param url * @return */ public static Drawable loadImageFromUrl(String url) { ByteArrayOutputStream out = null; Drawable drawable = null; int BUFFER_SIZE = 1024*16; InputStream inputStream = null; try{ inputStream = new URL(url).openStream(); BufferedInputStream in = new BufferedInputStream(inputStream, BUFFER_SIZE); out = new ByteArrayOutputStream(BUFFER_SIZE); int length = 0; byte[] tem = new byte[BUFFER_SIZE]; length = in.read(tem); while(length != -1){ out.write(tem, 0, length); length = in.read(tem); } in.close(); drawable = Drawable.createFromStream(new ByteArrayInputStream(out.toByteArray()), "src"); }catch(Exception e){ e.printStackTrace(); }finally{ if(inputStream != null){ try{ inputStream.close(); }catch(Exception e){} } } return drawable; } /** * 异步设置单张imageview图片,采取软引用 * @param url 网络图片地址 * @param imageView 需要设置的imageview */ public static void setImageViewFromUrl(final String url, final ImageView imageView){ singImageView = imageView; //如果软引用为空,就新建一个 if(singleImageCache == null){ singleImageCache = new HashMap<String, SoftReference<Drawable>>(); } //如果软引用中已经有了相同的地址,就从软引用中获取 if(singleImageCache.containsKey(url)){ SoftReference<Drawable> soft = singleImageCache.get(url); Drawable draw = soft.get(); singImageView.setImageDrawable(draw); return; } final Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { singImageView.setImageDrawable((Drawable)msg.obj); } }; //子线程不能更新UI,又不然会报错 new Thread(){ public void run() { Drawable drawable = loadImageFromUrl(url); if(drawable == null){ Log.e("single imageview", "single imageview of drawable is null"); }else{ //把已经读取到的图片放入软引用 singleImageCache.put(url, new SoftReference<Drawable>(drawable)); } Message message = handler.obtainMessage(0, drawable); handler.sendMessage(message); }; }.start(); } }

4,AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.cn" android:versionCode="1" android:versionName="1.0" > <uses-sdk android:minSdkVersion="8" /> <application android:icon="@drawable/ic_launcher" android:label="@string/app_name" > <activity android:label="@string/app_name" android:name=".AsyncImageViewActivity" > <intent-filter > <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> <uses-permission android:name="android.permission.INTERNET" /> </manifest>