Android 异步加载图片(AsyncImageLoader)
这个例子是利用AsyncTask异步下载图片，下载时先将网络图片下载到本地cache目录保存，以imagUrl的图片文件名保存，如果有同名文件在cache目录就从本地加载。
布局文件，先用一个图片占位：
<ImageView
android:id="@+id/image"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_gravity="center_horizontal"
android:layout_marginTop="20dip"
android:src="@drawable/product_default_icon" />
private Context context = AsyncTaskDemo.this;
private ImageView image;
//图片地址
private String imageUrl = "http://dl.iteye.com/upload/attachment/0080/1571/2b9a099a-0a7b-3a60-909e-97a8316716cb.jpg";
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.asynctask);
getWidget();
loadImage(imageUrl);
}
/** 获得组件 */
public void getWidget() {
image = (ImageView) findViewById(R.id.image);
}
private void loadImage(final String imageUrl) {
ImageAsyncLoader asyncImageLoader = new ImageAsyncLoader();
// 异步加载图片
Drawable cachedImage = asyncImageLoader.loadDrawable(context, imageUrl, new ImageCallback() {
public void imageLoaded(Drawable imageDrawable, String imageUrl) {
if (imageDrawable != null) {
image.setImageDrawable(ImageAsyncLoader.zoomDrawable(imageDrawable, ImageAsyncLoader.dip2px(context, 150), ImageAsyncLoader.dip2px(context, 150)));
}
}
});
if (cachedImage != null) {
image.setImageDrawable(ImageAsyncLoader.zoomDrawable(cachedImage, ImageAsyncLoader.dip2px(context, 150), ImageAsyncLoader.dip2px(context, 150)));
}
}
图片异步加载工具
private HashMap<String, SoftReference<Drawable>> cacheMap = null;
private BlockingQueue<Runnable> queue = null;
private ThreadPoolExecutor executor = null;
public ImageAsyncLoader() {
cacheMap = new HashMap<String, SoftReference<Drawable>>();
queue = new LinkedBlockingQueue<Runnable>();
/**
* 线程池维护线程的最少数量2 <br>
* 线程池维护线程的最大数量10<br>
* 线程池维护线程所允许的空闲时间180秒
*/
executor = new ThreadPoolExecutor(2, 10, 180, TimeUnit.SECONDS, queue);
}
public Drawable loadDrawable(final Context context, final String imageUrl, final ImageCallback imageCallback) {
if (cacheMap.containsKey(imageUrl)) {
SoftReference<Drawable> softReference = cacheMap.get(imageUrl);
Drawable drawable = softReference.get();
if (drawable != null) {
return drawable;
}
}
final Handler handler = new Handler() {
public void handleMessage(Message message) {
imageCallback.imageLoaded((Drawable) message.obj, imageUrl);
}
};
// 将任务添加到线程池
executor.execute(new Runnable() {
public void run() {
// 根据URL加载图片
Drawable drawable = loadImageFromUrl(context, imageUrl);
// 图片资源不为空是创建软引用
if (null != drawable)
cacheMap.put(imageUrl, new SoftReference<Drawable>(drawable));
Message message = handler.obtainMessage(0, drawable);
handler.sendMessage(message);
}
});
return null;
}
// 网络图片先下载到本地cache目录保存，以imagUrl的图片文件名保存，如果有同名文件在cache目录就从本地加载
public static Drawable loadImageFromUrl(Context context, String imageUrl) {
Drawable drawable = null;
if (imageUrl == null)
return null;
String fileName = "";
// 获取url中图片的文件名与后缀
if (imageUrl != null && imageUrl.length() != 0) {
fileName = imageUrl.substring(imageUrl.lastIndexOf("/") + 1);
}
// 根据图片的名称创建文件（不存在：创建）
File file = new File(context.getCacheDir(), fileName);
// 如果在缓存中找不到指定图片则下载
if (!file.exists() && !file.isDirectory()) {
try {
// 从网络上下载图片并写入文件
FileOutputStream fos = new FileOutputStream(file);
InputStream is = new URL(imageUrl).openStream();
int data = is.read();
while (data != -1) {
fos.write(data);
data = is.read();
}
fos.close();
is.close();
drawable = Drawable.createFromPath(file.toString());
} catch (IOException e) {
e.printStackTrace();
}
}
// 如果缓存中有则直接使用缓存中的图片
else {
// System.out.println(file.isDirectory() + " " + file.getName());
drawable = Drawable.createFromPath(file.toString());
}
return drawable;
}
public interface ImageCallback {
public void imageLoaded(Drawable imageDrawable, String imageUrl);
}
常用图片处理方法
/**
* 缩放Drawable
*
* @param drawable
* @param w 缩放后的宽
* @param h 缩放后的高
* @return Drawable
*/
public static Drawable zoomDrawable(Drawable drawable, int w, int h) {
int width = drawable.getIntrinsicWidth();
int height = drawable.getIntrinsicHeight();
// drawable转换成bitmap
Bitmap oldbmp = drawableToBitmap(drawable);
// 创建操作图片用的Matrix对象
Matrix matrix = new Matrix();
// 计算缩放比例
float scaleWidth = ((float) w / width);
float scaleHeight = ((float) h / height);
matrix.postScale(scaleWidth, scaleHeight);
// 设置缩放比例
Bitmap newbmp = Bitmap.createBitmap(oldbmp, 0, 0, width, height, matrix, true);
return new BitmapDrawable(newbmp);
}
/**
* 将drawable转换成bitmap
*
* @param drawable
* @return Bitmap
*/
private static Bitmap drawableToBitmap(Drawable drawable) {
// 取drawable的长宽
int width = drawable.getIntrinsicWidth();
int height = drawable.getIntrinsicHeight();
Bitmap.Config config = drawable.getOpacity() != PixelFormat.OPAQUE ? Bitmap.Config.ARGB_8888 : Bitmap.Config.RGB_565; // 取drawable的颜色格式
Bitmap bitmap = Bitmap.createBitmap(width, height, config);
Canvas canvas = new Canvas(bitmap);
drawable.setBounds(0, 0, width, height);
drawable.draw(canvas);
return bitmap;
}
/**
* 单位转换：dip => px
*
* @param ctx 上下文环境
* @param dipValue
* @return
*/
public static int dip2px(Context ctx, int dipValue) {
final float scale = ctx.getResources().getDisplayMetrics().density;
return (int) (dipValue * scale);
}
配置文件
<uses-permission android:name="android.permission.CHANGE_NETWORK_STATE" /> <uses-permission android:name="android.permission.INTERNET" />