Android 图像异步加载之Android-Universal-Image-Loader_universalimageloader loadimagesync 缩放

• 多线程加载图像Multithread image loading (async or sync)
• 宽泛的自定义配置Wide customization of ImageLoader's configuration (thread executors, downloader, decoder, memory and disk cache, display image options, etc.)
• Many customization options for every display image call (stub images, caching switch, decoding options, Bitmap processing and displaying, etc.)
• 图像缓存Image caching in memory and/or on disk (device's file system or SD card)
• 加载过程监听Listening loading process (including downloading progress)

<dependency>
    <groupId>com.nostra13.universalimageloader</groupId>
    <artifactId>universal-image-loader</artifactId>
    <version>1.9.3</version>
</dependency>

compile 'com.nostra13.universalimageloader:universal-image-loader:1.9.3'

添加网络和SD卡权限：

<uses-permission android:name="android.permission.INTERNET" />
    <!-- Include following permission if you want to cache images on SD card -->
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

预配置Application or Activity class (before the first usage of ImageLoader)

// Create global configuration and initialize ImageLoader with this config
        ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(this)
            ...
            .build();
        ImageLoader.getInstance().init(config);

Acceptable URIs examples

"http://site.com/image.png" // from Web
"file:///mnt/sdcard/image.png" // from SD card
"file:///mnt/sdcard/video.mp4" // from SD card (video thumbnail)
"content://media/external/images/media/13" // from content provider
"content://media/external/video/media/13" // from content provider (video thumbnail)
"assets://image.png" // from assets
"drawable://" + R.drawable.img // from drawables (non-9patch images)

示例

imageLoader.displayImage(imageUri, imageView);
imageLoader.loadImage(imageUri, new SimpleImageLoadingListener() {
    @Override
    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
        // Do whatever you want with Bitmap
    }
});
// Load image, decode it to Bitmap and return Bitmap synchronously
Bitmap bmp = imageLoader.loadImageSync(imageUri);
// Load image, decode it to Bitmap and return Bitmap to callback
ImageSize targetSize = new ImageSize(80, 50); // result Bitmap will be fit to this size
imageLoader.loadImage(imageUri, targetSize, options, new SimpleImageLoadingListener() {
    @Override
    public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
        // Do whatever you want with Bitmap
    }
});
// Load image, decode it to Bitmap and return Bitmap synchronously
ImageSize targetSize = new ImageSize(80, 50); // result Bitmap will be fit to this size
Bitmap bmp = imageLoader.loadImageSync(imageUri, targetSize, options);

// DON'T COPY THIS CODE TO YOUR PROJECT! This is just example of ALL options using.
// See the sample project how to use ImageLoader correctly.
File cacheDir = StorageUtils.getCacheDirectory(context);
ImageLoaderConfiguration config = new ImageLoaderConfiguration.Builder(context)
        .memoryCacheExtraOptions(480, 800) // default = device screen dimensions 推荐
        .diskCacheExtraOptions(480, 800, null) //.推荐diskCacheExtraOptions(480, 800, null)
        .taskExecutor(...)
        .taskExecutorForCachedImages(...)
        .threadPoolSize(3) // default 推荐1-5
        .threadPriority(Thread.NORM_PRIORITY - 2) // default
        .tasksProcessingOrder(QueueProcessingType.FIFO) // default
        .denyCacheImageMultipleSizesInMemory()  //设置内存缓存不允许缓存一张图片的多个尺寸，默认允许。
        .memoryCache(new LruMemoryCache(2 * 1024 * 1024)) //使用强引用的缓存使用它，不过推荐使用weak与strong引用结合的UsingFreqLimitedMemoryCache或者使用全弱引用的WeakMemoryCache
        .memoryCacheSize(2 * 1024 * 1024)
        .memoryCacheSizePercentage(13) // default
        .diskCache(new UnlimitedDiscCache(cacheDir)) // default
        .diskCacheSize(50 * 1024 * 1024)
        .diskCacheFileCount(100)
        .diskCacheFileNameGenerator(new HashCodeFileNameGenerator()) // default
        .imageDownloader(new BaseImageDownloader(context)) // default
        .imageDecoder(new BaseImageDecoder()) // default
        .defaultDisplayImageOptions(DisplayImageOptions.createSimple()) // default
        .writeDebugLogs()
        .build();

示例配置缓存目录

File cacheDir = StorageUtils.getOwnCacheDirectory(getApplicationContext(), "imageloader/Cache");  

.diskCache(new UnlimitedDiscCache(cacheDir))//自定义缓存路径  

配置Display Options

// DON'T COPY THIS CODE TO YOUR PROJECT! This is just example of ALL options using.
// See the sample project how to use ImageLoader correctly.
DisplayImageOptions options = new DisplayImageOptions.Builder()
        .showImageOnLoading(R.drawable.ic_stub) // resource or drawable
        .showImageForEmptyUri(R.drawable.ic_empty) // resource or drawable
        .showImageOnFail(R.drawable.ic_error) // resource or drawable
        .resetViewBeforeLoading(false)  // default
        .delayBeforeLoading(1000)
        .cacheInMemory(false) // default
        .cacheOnDisk(false) // default
        .preProcessor(...)
        .postProcessor(...)
        .extraForDownloader(...)
        .considerExifParams(false) // default
        .imageScaleType(ImageScaleType.IN_SAMPLE_POWER_OF_2) // default 推荐.imageScaleType(ImageScaleType.EXACTLY) 节省内存
        .bitmapConfig(Bitmap.Config.ARGB_8888) // default 推荐.bitmapConfig(Bitmap.Config.RGB_565)节省内存
        .decodingOptions(...)
        .displayer(new SimpleBitmapDisplayer()) // default 
<span style="white-space:pre">		</span>/*推荐使用RoundedBitmapDisplayer (Displays bitmap with rounded corners)和
<span style="white-space:pre">		</span>*FadeInBitmapDisplayer (Displays image with "fade in" animation
<span style="white-space:pre">		</span>*但是使用RoundedBitmapDisplayer有些必要的注意事项，看后面提示。
<span style="white-space:pre">		</span>*/
        .handler(new Handler()) // default
        .build();

• This implementation works only with ImageViews wrapped in ImageViewAware否则会出现异常ImageAware should wrap ImageView. ImageViewAware is expected.出现这种异常只能注释掉设置代码。
• If this implementation doesn't meet your needs then consider RoundedImageView or CircularImageView projects for usage.

注意的问题

// Create default options which will be used for every 
//  displayImage(...) call if no options will be passed to this method
DisplayImageOptions defaultOptions = new DisplayImageOptions.Builder()
        ...
        .cacheInMemory(true)
        .cacheOnDisk(true)<pre name="code" class="java">boolean pauseOnScroll = false; // or true
boolean pauseOnFling = true; // or false
PauseOnScrollListener listener = new PauseOnScrollListener(imageLoader, pauseOnScroll, pauseOnFling);
listView.setOnScrollListener(listener);

// Then later, when you want to display image
ImageLoader.getInstance().displayImage(imageUrl, imageView); // Default options will be used

DisplayImageOptions options = new DisplayImageOptions.Builder()
        ...
        .cacheInMemory(true)
        .cacheOnDisk(true)
        ...
        .build();
ImageLoader.getInstance().displayImage(imageUrl, imageView, options); // Incoming options will be used

boolean pauseOnScroll = false; // or true
boolean pauseOnFling = true; // or false
PauseOnScrollListener listener = new PauseOnScrollListener(imageLoader, pauseOnScroll, pauseOnFling);
listView.setOnScrollListener(listener);

To generate the rounded images I simply wrote a custom Drawable that draws a rounded rectangle using Canvas.drawRoundRect(). The trick is to use a Paint with a BitmapShader to fill the rounded rectangle with a texture instead of a simple color. Here is what the code looks like:
 
BitmapShader shader;
shader = new BitmapShader(bitmap, Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
 
Paint paint = new Paint();
paint.setAntiAlias(true);
paint.setShader(shader);
 
RectF rect = new RectF(0.0f, 0.0f, width, height);
 
// rect contains the bounds of the shape
// radius is the radius in pixels of the rounded corners
// paint contains the shader that will texture the shape
canvas.drawRoundRect(rect, radius, radius, paint);