android volley 源码

/** * Copyright (C) 2013 The Android Open Source Project * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package com.android.volley.toolbox; import android.graphics.Bitmap; import android.graphics.Bitmap.Config; import android.os.Handler; import android.os.Looper; import android.widget.ImageView; import com.android.volley.Request; import com.android.volley.RequestQueue; import com.android.volley.Response.ErrorListener; import com.android.volley.Response.Listener; import com.android.volley.VolleyError; import com.android.volley.toolbox.ImageRequest; import java.util.HashMap; import java.util.LinkedList; /** * Helper that handles loading and caching images from remote URLs. * * The simple way to use this class is to call {@link ImageLoader#get(String, ImageListener)} * and to pass in the default image listener provided by * {@link ImageLoader#getImageListener(ImageView, int, int)}. Note that all function calls to * this class must be made from the main thead, and all responses will be delivered to the main * thread as well. */ public class ImageLoader { /** RequestQueue for dispatching ImageRequests onto. */ private final RequestQueue mRequestQueue; /** Amount of time to wait after first response arrives before delivering all responses. */ private int mBatchResponseDelayMs = 100; /** The cache implementation to be used as an L1 cache before calling into volley. */ private final ImageCache mCache; /** * HashMap of Cache keys -> BatchedImageRequest used to track in-flight requests so * that we can coalesce multiple requests to the same URL into a single network request. */ private final HashMap<String, BatchedImageRequest> mInFlightRequests = new HashMap<String, BatchedImageRequest>(); /** HashMap of the currently pending responses (waiting to be delivered). */ private final HashMap<String, BatchedImageRequest> mBatchedResponses = new HashMap<String, BatchedImageRequest>(); /** Handler to the main thread. */ private final Handler mHandler = new Handler(Looper.getMainLooper()); /** Runnable for in-flight response delivery. */ private Runnable mRunnable; /** * Simple cache adapter interface. If provided to the ImageLoader, it * will be used as an L1 cache before dispatch to Volley. Implementations * must not block. Implementation with an LruCache is recommended. */ public interface ImageCache { public Bitmap getBitmap(String url); public void putBitmap(String url, Bitmap bitmap); } /** * Constructs a new ImageLoader. * @param queue The RequestQueue to use for making image requests. * @param imageCache The cache to use as an L1 cache. */ public ImageLoader(RequestQueue queue, ImageCache imageCache) { mRequestQueue = queue; mCache = imageCache; } /** * The default implementation of ImageListener which handles basic functionality * of showing a default image until the network response is received, at which point * it will switch to either the actual image or the error image. * @param imageView The imageView that the listener is associated with. * @param defaultImageResId Default image resource ID to use, or 0 if it doesn't exist. * @param errorImageResId Error image resource ID to use, or 0 if it doesn't exist. */ 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); } } }; } /** * Interface for the response handlers on image requests. * * The call flow is this: * 1. Upon being attached to a request, onResponse(response, true) will * be invoked to reflect any cached data that was already available. If the * data was available, response.getBitmap() will be non-null. * * 2. After a network response returns, only one of the following cases will happen: * - onResponse(response, false) will be called if the image was loaded. * or * - onErrorResponse will be called if there was an error loading the image. */ public interface ImageListener extends ErrorListener { /** * Listens for non-error changes to the loading of the image request. * * @param response Holds all information pertaining to the request, as well * as the bitmap (if it is loaded). * @param isImmediate True if this was called during ImageLoader.get() variants. * This can be used to differentiate between a cached image loading and a network * image loading in order to, for example, run an animation to fade in network loaded * images. */ public void onResponse(ImageContainer response, boolean isImmediate); } /** * Checks if the item is available in the cache. * @param requestUrl The url of the remote image * @param maxWidth The maximum width of the returned image. * @param maxHeight The maximum height of the returned image. * @return True if the item exists in cache, false otherwise. */ public boolean isCached(String requestUrl, int maxWidth, int maxHeight) { throwIfNotOnMainThread(); String cacheKey = getCacheKey(requestUrl, maxWidth, maxHeight); return mCache.getBitmap(cacheKey) != null; } /** * Returns an ImageContainer for the requested URL. * * The ImageContainer will contain either the specified default bitmap or the loaded bitmap. * If the default was returned, the {@link ImageLoader} will be invoked when the * request is fulfilled. * * @param requestUrl The URL of the image to be loaded. * @param defaultImage Optional default image to return until the actual image is loaded. */ public ImageContainer get(String requestUrl, final ImageListener listener) { return get(requestUrl, listener, 0, 0); } /** * Issues a bitmap request with the given URL if that image is not available * in the cache, and returns a bitmap container that contains all of the data * relating to the request (as well as the default image if the requested * image is not available). * @param requestUrl The url of the remote image * @param imageListener The listener to call when the remote image is loaded * @param maxWidth The maximum width of the returned image. * @param maxHeight The maximum height of the returned image. * @return A container object that contains all of the properties of the request, as well as * the currently available image (default if remote is not loaded). */ public ImageContainer get(String requestUrl, ImageListener imageListener, int maxWidth, int maxHeight) {