volley基本应用

<span style="font-size:18px;">/** *  * Volley是Android平台网络通信库：更快。更简单。更健壮 volley提供的功能： 1.JSON、图片（异步） 2.网络请求的排序 * 3.网络请求的优先级处理 4.缓存 5.多级别的取消请求 6.与Activity生命周期联动 * 适合网络请求频换，数据量不是很大的 网络请求**** *  * 获取Volley git clone * https://android.googlesource.com/platform/frameworks/volley *  *  *  *  *  */public class MainActivity extends Activity {private ImageView iv1;private NetworkImageView iv2;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);init();getJSONVolley();}public void init() {iv1 = (ImageView) findViewById(R.id.iv);iv2 = (NetworkImageView) findViewById(R.id.imageView1);loadImageVolley();NetWorkImageViewVolley();}// 获取json字符串public void getJSONVolley() {RequestQueue requestQueue = Volley.newRequestQueue(this);String JSONDateUrl = "http://www.wwtliu.com/jsondata.html";JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, JSONDateUrl, null,new Response.Listener<JSONObject>() {public void onResponse(JSONObject response) {System.out.println("response=" + response);}}, new Response.ErrorListener() {public void onErrorResponse(com.android.volley.VolleyError arg0) {System.out.println("对不起，有问题");}});requestQueue.add(jsonObjectRequest);}// http://localhost/lesson-img.pngpublic void loadImageVolley() {String imageurl = "http://10.0.0.52/lesson-img.png";RequestQueue requestQueue = Volley.newRequestQueue(this);final LruCache<String, Bitmap> lurcache = new LruCache<String, Bitmap>(20);ImageCache imageCache = new ImageCache() {@Overridepublic void putBitmap(String key, Bitmap value) {lurcache.put(key, value);}@Overridepublic Bitmap getBitmap(String key) {return lurcache.get(key);}};ImageLoader imageLoader = new ImageLoader(requestQueue, imageCache);ImageListener listener = imageLoader.getImageListener(iv1,R.drawable.ic_launcher, R.drawable.ic_launcher);imageLoader.get(imageurl, listener);}public void NetWorkImageViewVolley(){String imageUrl = "http://10.0.0.52/lesson-img.png";RequestQueue requestQueue = Volley.newRequestQueue(this);final LruCache<String, Bitmap> lruCache = new LruCache<String, Bitmap>(20);ImageCache imageCache = new ImageCache() {@Overridepublic void putBitmap(String key, Bitmap value) {lruCache.put(key, value);}@Overridepublic Bitmap getBitmap(String key) {return lruCache.get(key);}};ImageLoader imageLoader = new ImageLoader(requestQueue, imageCache);iv2.setTag("url");iv2.setImageUrl(imageUrl, imageLoader);}}</span>

 

tv1 设置图片的方法  看源代码：

<span style="font-size:18px;">   public ImageLoader(RequestQueue queue, ImageCache imageCache) {        mRequestQueue = queue;        mCache = imageCache;    }</span>

初始化imageloader

<span style="font-family:Arial;font-size:18px;BACKGROUND-COLOR: #ffffff"></span> 

<span style="font-size:18px;">    public class ImageContainer {        /**         * The most relevant bitmap for the container. If the image was in cache, the         * Holder to use for the final bitmap (the one that pairs to the requested URL).         */        private Bitmap mBitmap;图片        private final ImageListener mListener;监听        /** The cache key that was associated with the request */        private final String mCacheKey;缓存的key        /** The request URL that was specified */        private final String mRequestUrl;请求URL</span>

ImageContainer 封装了图片和 监听 key URL

<span style="font-size:18px;">    public static ImageListener getImageListener(final ImageView view,            final int defaultImageResId, final int errorImageResId) {        return new ImageListener() {            @Override            public void onErrorResponse(VolleyError error) {                if (errorImageResId != 0) {                    view.setImageResource(errorImageResId);                }            }            @Override            public void onResponse(ImageContainer response, boolean isImmediate) {                if (response.getBitmap() != null) {                    view.setImageBitmap(response.getBitmap());                } else if (defaultImageResId != 0) {                    view.setImageResource(defaultImageResId);                }            }        };    }</span>

onResponse(ImageContainer response, boolean isImmediate)  传进来 ImageContainer 参数  

<span style="font-size:18px;"> public ImageContainer get(String requestUrl, ImageListener imageListener,            int maxWidth, int maxHeight) {        // only fulfill requests that were initiated from the main thread.        throwIfNotOnMainThread();        final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight);        // Try to look up the request in the cache of remote images.        Bitmap cachedBitmap = mCache.getBitmap(cacheKey);        //如果缓存有图片        if (cachedBitmap != null) {                       ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, null, null);            //回调给  监听  返回缓存的图片            imageListener.onResponse(container, true);            return container;        }       //如果无缓存图片        ImageContainer imageContainer =                new ImageContainer(null, requestUrl, cacheKey, imageListener);        // Update the caller to let them know that they should use the default bitmap.        imageListener.onResponse(imageContainer, true);        // Check to see if a request is already in-flight.        BatchedImageRequest request = mInFlightRequests.get(cacheKey);        if (request != null) {            // If it is, add this request to the list of listeners.            request.addContainer(imageContainer);            return imageContainer;        }        Request<?> newRequest =            new ImageRequest(requestUrl, new Listener<Bitmap>() {                @Override                public void onResponse(Bitmap response) {                    onGetImageSuccess(cacheKey, response);                }            }, maxWidth, maxHeight,            Config.RGB_565, new ErrorListener() {                @Override                public void onErrorResponse(VolleyError error) {                    onGetImageError(cacheKey, error);                }            });        mRequestQueue.add(newRequest);        mInFlightRequests.put(cacheKey,                new BatchedImageRequest(newRequest, imageContainer));        return imageContainer;    }</span>

 final String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight);   用URL 生成一个 唯一标识的key
        Bitmap cachedBitmap = mCache.getBitmap(cacheKey); 获取缓图片

接着 判断是否cachedBitmap！=null 是的话构造ImageContainer 将图片和URL封装起来。

ImageContainer container = new ImageContainer(cachedBitmap, requestUrl, null, null);
            //调用imagelistener监听方法传递 封装好的ImageContainer
            imageListener.onResponse(container, true);

如果没缓存图片

ImageContainer imageContainer =  new ImageContainer(null, requestUrl, cacheKey, imageListener);

imageListener.onResponse(imageContainer, true);

第一个参数Bitmap 为null  封装URL key image监听  其实就是回调接口 ImageView设置默认图片

 

接着BatchedImageRequest request = mInFlightRequests.get(cacheKey);  判断这个集合是否有这个请求 用于

如果request ！=null

 request.addContainer(imageContainer);

 return imageContainer;上面例子iv2 返回 imageContainer  

接下来代码

<span style="font-size:18px;">Request<?> newRequest =            new ImageRequest(requestUrl, new Listener<Bitmap>() {                @Override                public void onResponse(Bitmap response) {                // 成功获取网络图片                     onGetImageSuccess(cacheKey, response);                }            }, maxWidth, maxHeight,            Config.RGB_565, new ErrorListener() {                @Override                public void onErrorResponse(VolleyError error) {                    onGetImageError(cacheKey, error);                }            });</span>

因为缓存没图片 说明第一次请求或者删除了  。重新构造请求

 onGetImageSuccess(cacheKey, response);

<span style="font-size:18px;">mRequestQueue.add(newRequest);  mInFlightRequests.put(cacheKey, new BatchedImageRequest(newRequest, imageContainer));</span>

然后 添加到请求队列  和mInFlightRequests 集合中  new BatchedImageRequest的时候

<span style="font-size:18px;"> public BatchedImageRequest(Request<?> request, ImageContainer container) {            mRequest = request;            mContainers.add(container);        }</span>

把ImageContainer 加到BatchedImageRequest 类成员变量 集合中

<span style="font-size:18px;">  /**     * Handler for when an image was successfully loaded.     * @param cacheKey The cache key that is associated with the image request.     * @param response The bitmap that was returned from the network.     */    private void onGetImageSuccess(String cacheKey, Bitmap response) {        // cache the image that was fetched.        mCache.putBitmap(cacheKey, response);        // remove the request from the list of in-flight requests.        BatchedImageRequest request = mInFlightRequests.remove(cacheKey);        if (request != null) {            // Update the response bitmap.            request.mResponseBitmap = response;            // Send the batched response            batchResponse(cacheKey, request);        }    }</span>

mCache.putBitmap(cacheKey, response); 把图片缓存起来

mInFlightRequests这个请求hasmap中是否已经包含你想要下载的图片，如果有，将这个请求加入到批量处理的请求（BatchedImageRequest）中， 为什么要这样做？其实volley是想帮你解决这样一种情况：假如有2个地方都需要下载同样的图片，而这张图片并没有下载完成（也就是说没办法去缓存中取图片数据），那么volley就会把这两个请求都保存起来，当下载完成后，统一返回给这2个请求的view，这样就不需要下载2遍重复的请求

<span style="font-size:18px;">private void batchResponse(String cacheKey, BatchedImageRequest request) {        mBatchedResponses.put(cacheKey, request);        // If we don't already have a batch delivery runnable in flight, make a new one.        // Note that this will be used to deliver responses to all callers in mBatchedResponses.        if (mRunnable == null) {            mRunnable = new Runnable() {                @Override                public void run() {                //遍历 批处理request                    for (BatchedImageRequest bir : mBatchedResponses.values()) {                        for (ImageContainer container : bir.mContainers) {                            // If one of the callers in the batched request canceled the request                            // after the response was received but before it was delivered,                            // skip them.                            if (container.mListener == null) {                                continue;                            }                            if (bir.getError() == null) {                                container.mBitmap = bir.mResponseBitmap;                                container.mListener.onResponse(container, false);                            } else {                                container.mListener.onErrorResponse(bir.getError());                            }                        }                    }                    mBatchedResponses.clear();                    mRunnable = null;                }            };            // Post the runnable.            mHandler.postDelayed(mRunnable, mBatchResponseDelayMs);        }    }</span>

 

container.mBitmap = bir.mResponseBitmap; 

变量得到请求中的ImageContainer 
container.mListener.onResponse(container, false);