关于ImageLoader

关于ImageLoader

universal-image-loader是最常用的网络图片加载的开源框架.
当然volley中也又ImageLoader类,但是它的强项仅仅在于对网络图片的加载,还需要自己做L2的缓存,已经对于多样化的图片显示不是特别的方便(圆角,圆形,模糊显示).

简介:

Gradle dependency:
compile 'com.nostra13.universalimageloader:universal-image-loader:1.9.4'

ImageLoaderConfiguration

在第一次使用的之前,初始化ImageLoaderConfiguration,这是初始化一个ImageLoader的默认配置.例如:

// 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
    .diskCacheExtraOptions(480, 800, null)
    .taskExecutor(...)
    .taskExecutorForCachedImages(...)
    .threadPoolSize(3) // default
    .threadPriority(Thread.NORM_PRIORITY - 2) // default
    .tasksProcessingOrder(QueueProcessingType.FIFO) // default
    .denyCacheImageMultipleSizesInMemory()
    .memoryCache(new LruMemoryCache(2 * 1024 * 1024))
    .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(); 

1. .diskCache(new UnlimitedDiscCache(cacheDir))设置disk缓存的路径
2. .threadPoolSize(3) 设置线程池的线程数量
3. .memoryCache(new LruMemoryCache(2 * 1024 * 1024)) 设置内存缓存的大小

通过自定义设置ImageLoaderConfiguration,满足自己的对于ImageLoader的使用.

DisplayImageOptions

每一张图片的显示,其实都是一个任务.用ImageLoader.displayImage(…).很多时候,我们对于不同位置的图片,想展示不同的样式.例如A位置我想展示圆角的图片,而B位置却想展示直角的图片.那么这个时候,就需要设置DisplayImageOptions这个选项参数.如果不传,就会使用默认的Options,那么那个就是在前面说的ImageLoaderConfiguration中设置的.

以下是关于DisplayImageOptions的设置:

// 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
    .bitmapConfig(Bitmap.Config.ARGB_8888) // default
    .decodingOptions(...)
    .displayer(new SimpleBitmapDisplayer()) // default
    .handler(new Handler()) // default
    .build();

1. .showImageOnLoading() 设置图片加载中时使用的默认图片
2. .cacheInMemory() 是否缓存到内存中

就是一下基本的方法.如果有需要,我们会在后面详细分析.

ImageLoader能够加载的图片类型:

1. “http://site.com/image.png” // from Web
2. “file:///mnt/sdcard/image.png” // from SD card
3. “file:///mnt/sdcard/video.mp4” // from SD card (video thumbnail)
4. “content://media/external/images/media/13” // from content provider
5. “content://media/external/video/media/13” // from content provider (video thumbnail)
6. “assets://image.png” // from assets
7. “drawable://” + R.drawable.img // from drawables (non-9patch images)

Note: 作者建议我们在显示drawble://的时候,考虑使用原生的方法,ImageView.setImageResource()来替代.

使用:

1. 获取ImageLoader的单例

    ImageLoader imageLoader = ImageLoader.getInstance(); // Get singleton instance
   

2. 加载一个图片,对该图片解码成一个Bitmap,然后再ImageView中显示(或者是其它实现了ImageAware接口的View).3.

   • 可以直接调用displayImage方法,用默认的options

       imageLoader.displayImage(imageUri, imageView);
     

   • 可以定义SimpleImageLoadingListener,ImageLoaderListener或者ImageLoadingProgressListener,在加载的各个状态中回调.

       imageLoader.loadImage(imageUri, new SimpleImageLoadingListener() {
      		@Override
      		public void onLoadingComplete(String imageUri, View view, Bitmap loadedImage) {
       			// Do whatever you want with Bitmap}
       		}
       	);
     

   • 可以同步下载一个Bitmap图片

     // Load image, decode it to Bitmap and return Bitmap synchronously

       Bitmap bmp = imageLoader.loadImageSync(imageUri);
     

   • 可以定义下载图片的尺寸,利用ImageSize

       // 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);
     

Useful Info:

1. 默认情况下是不缓存的.所以需要通过默认的DisplayImageOptions,并把设置其中的.cacheInMemory和.cacheOnDisk,然后把定义好的option,设置到ImageLoaderConfiguration中.defaultDisplayImageOptions(defaultOptions)方法.
2. 如果使用了ImageLoader出现OutOfMemoryError的话,那么可以通过
   • 关闭memory的cache
   • 减少线程池的大小
   • 用Bitmap.Config.RGB_565代替ARGB_8888
   • 使用.imageScaleType(ImageScaleType.EXACTLY)
   • 使用.diskCacheExtraOption(480, 320, null)
3. 关于内存缓存的设置,有一些实现好的实现策略:
   • 只有强引用
     • LruMemoryCache (Least recently used bitmap is deleted when cache size limit is exceeded) - Used by default
   • 强引用和弱引用混合用
     • UsingFreqLimitedMemoryCache (Least frequently used bitmap is deleted when cache size limit is exceeded)
     • LRULimitedMemoryCache (Least recently used bitmap is deleted when cache size limit is exceeded)
     • FIFOLimitedMemoryCache (FIFO rule is used for deletion when cache size limit is exceeded)
     • LargestLimitedMemoryCache (The largest bitmap is deleted when cache size limit is exceeded)
     • LimitedAgeMemoryCache (Decorator. Cached object is deleted when its age exceeds defined value)
   • 只有弱引用
     • WeakMemoryCache (Unlimited cache)
4. 关于disk缓存的配置,一些已经实现好的策略:
   • UnlimitedDiscCache (The fastest cache, doesn’t limit cache size) - Used by default
   • LruDiskCache (Cache limited by total cache size and/or by file count. If cache size exceeds specified limit then least-recently used file will be deleted)
   • LimitedAgeDiscCache (Size-unlimited cache with limited files’ lifetime. If age of cached file exceeds defined limit then it will be deleted from cache.)
     NOTE: UnlimitedDiscCache 是速度最快的实现方式.
5. 展示bitmap的时候,有两个已经实现好的方法:
   • 显示圆角 RoundedBitmapDisplayer (Displays bitmap with rounded corners)
   • 淡入显示 FadeInBitmapDisplayer (Displays image with “fade in” animation)

6. 如果不想在list或者grid滑动的过程中,加载图片.可以通过设置PauseOnScrollListener:

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

参考1
参考2