我只是個搬運工,文章轉自:http://blog.csdn.net/xu_fu/article/details/17043231
感謝xu_fu的幫助~
picasso是Square公司開源的一個Android圖形緩存庫,地址http://square.github.io/picasso/,可以實現圖片下載和緩存功能。
picasso使用簡單,如下
- Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);
主要有以下一些特性:
- 在adapter中回收和取消當前的下載;
- 使用最少的內存完成複雜的圖形轉換操作;
- 自動的內存和硬盤緩存;
- 圖形轉換操作,如變換大小,旋轉等,提供了接口來讓用戶可以自定義轉換操作;
- 加載載網絡或本地資源;
代碼分析
Cache,緩存類
- this.map = new LinkedHashMap<String, Bitmap>(0, 0.75f, true);
最後一個參數的解釋:
- private void trimToSize(int maxSize) {
- while (true) {
- String key;
- Bitmap value;
- synchronized (this) {
- if (size < 0 || (map.isEmpty() && size != 0)) {
- throw new IllegalStateException(getClass().getName()
- + ".sizeOf() is reporting inconsistent results!");
- }
- if (size <= maxSize || map.isEmpty()) {
- break;
- }
- Map.Entry<String, Bitmap> toEvict = map.entrySet().iterator()
- .next();
- key = toEvict.getKey();
- value = toEvict.getValue();
- map.remove(key);
- size -= Utils.getBitmapBytes(value);
- evictionCount++;
- }
- }
- }
Request,操作封裝類
- public interface Transformation {
- /**
- * Transform the source bitmap into a new bitmap. If you create a new bitmap instance, you must
- * call {@link android.graphics.Bitmap#recycle()} on {@code source}. You may return the original
- * if no transformation is required.
- */
- Bitmap transform(Bitmap source);
- /**
- * Returns a unique key for the transformation, used for caching purposes. If the transformation
- * has parameters (e.g. size, scale factor, etc) then these should be part of the key.
- */
- String key();
- }
當操作封裝好以後,會將Request傳到另一個結構中Action。
Action
- @Override
- public void complete(Bitmap result, Picasso.LoadedFrom from) {
- if (result == null) {
- throw new AssertionError(String.format(
- "Attempted to complete action with no result!\n%s", this));
- }
- ImageView target = this.target.get();
- if (target == null) {
- return;
- }
- Context context = picasso.context;
- boolean debugging = picasso.debugging;
- PicassoDrawable.setBitmap(target, context, result, from, noFade,
- debugging);
- if (callback != null) {
- callback.onSuccess();
- }
- }
有了加載任務,具體的圖片下載與解析是在哪裏呢?這些都是耗時的操作,應該放在異步線程中進行,就是下面的BitmapHunter。
BitmapHunter
- @Override
- public void run() {
- try {
- Thread.currentThread()
- .setName(Utils.THREAD_PREFIX + data.getName());
- result = hunt();
- if (result == null) {
- dispatcher.dispatchFailed(this);
- } else {
- dispatcher.dispatchComplete(this);
- }
- } catch (IOException e) {
- exception = e;
- dispatcher.dispatchRetry(this);
- } catch (Exception e) {
- exception = e;
- dispatcher.dispatchFailed(this);
- } finally {
- Thread.currentThread().setName(Utils.THREAD_IDLE_NAME);
- }
- }
- abstract Bitmap decode(Request data) throws IOException;
- Bitmap hunt() throws IOException {
- Bitmap bitmap;
- if (!skipMemoryCache) {
- bitmap = cache.get(key);
- if (bitmap != null) {
- stats.dispatchCacheHit();
- loadedFrom = MEMORY;
- return bitmap;
- }
- }
- bitmap = decode(data);
- if (bitmap != null) {
- stats.dispatchBitmapDecoded(bitmap);
- if (data.needsTransformation() || exifRotation != 0) {
- synchronized (DECODE_LOCK) {
- if (data.needsMatrixTransform() || exifRotation != 0) {
- bitmap = transformResult(data, bitmap, exifRotation);
- }
- if (data.hasCustomTransformations()) {
- bitmap = applyCustomTransformations(
- data.transformations, bitmap);
- }
- }
- stats.dispatchBitmapTransformed(bitmap);
- }
- }
- return bitmap;
- }
可以看到,在decode生成原始bitmap,之後會做需要的轉換transformResult和applyCustomTransformations。最後在將最終的結果傳遞到上層dispatcher.dispatchComplete(this)。
Dispatcher任務調度器
外部調用的是dispatchXXX方法,然後通過handler將請求轉換到對應的performXXX方法。
例如生成Action以後就會調用dispather的dispatchSubmit()來請求執行,
- void dispatchSubmit(Action action) {
- handler.sendMessage(handler.obtainMessage(REQUEST_SUBMIT, action));
- }
handler接到消息後轉換到performSubmit方法
- void performSubmit(Action action) {
- BitmapHunter hunter = hunterMap.get(action.getKey());
- if (hunter != null) {
- hunter.attach(action);
- return;
- }
- if (service.isShutdown()) {
- return;
- }
- hunter = forRequest(context, action.getPicasso(), this, cache, stats,
- action, downloader);
- hunter.future = service.submit(hunter);
- hunterMap.put(action.getKey(), hunter);
- }
這裏將通過action得到具體的BitmapHunder,然後交給ExecutorService執行。
- public static Picasso with(Context context) {
- if (singleton == null) {
- singleton = new Builder(context).build();
- }
- return singleton;
- }
- public Picasso build() {
- Context context = this.context;
- if (downloader == null) {
- downloader = Utils.createDefaultDownloader(context);
- }
- if (cache == null) {
- cache = new LruCache(context);
- }
- if (service == null) {
- service = new PicassoExecutorService();
- }
- if (transformer == null) {
- transformer = RequestTransformer.IDENTITY;
- }
- Stats stats = new Stats(cache);
- Dispatcher dispatcher = new Dispatcher(context, service, HANDLER,
- downloader, cache, stats);
- return new Picasso(context, dispatcher, cache, listener,
- transformer, stats, debugging);
- }
在Picasso.with()的時候會將執行所需的所有必備元素創建出來,如緩存cache、執行executorService、調度dispatch等,在load()時創建Request,在into()中創建action、bitmapHunter,並最終交給dispatcher執行。