SDWebImage源码学习之由浅入深 二
接上篇分析SDWebImage源码学习之由浅入深 一
if (url) {
// check if activityView is enabled or not
if ([self sd_showActivityIndicatorView]) {
[self sd_addActivityIndicator];
}
__weak __typeof(self)wself = self;
id operation = [SDWebImageManager.sharedManager loadImageWithURL:url options:options progress:progressBlock completed:^(UIImage *image, NSData *data, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
__strong __typeof (wself) sself = wself;
[sself sd_removeActivityIndicator];
if (!sself) {
return;
}
dispatch_main_async_safe(^{
if (!sself) {
return;
}
if (image && (options & SDWebImageAvoidAutoSetImage) && completedBlock) {
completedBlock(image, error, cacheType, url);
return;
} else if (image) {
[sself sd_setImage:image imageData:data basedOnClassOrViaCustomSetImageBlock:setImageBlock];
[sself sd_setNeedsLayout];
} else {
if ((options & SDWebImageDelayPlaceholder)) {
[sself sd_setImage:placeholder imageData:nil basedOnClassOrViaCustomSetImageBlock:setImageBlock];
[sself sd_setNeedsLayout];
}
}
if (completedBlock && finished) {
completedBlock(image, error, cacheType, url);
}
});
}];
[self sd_setImageLoadOperation:operation forKey:validOperationKey];
} else {
dispatch_main_async_safe(^{
[self sd_removeActivityIndicator];
if (completedBlock) {
NSError *error = [NSError errorWithDomain:SDWebImageErrorDomain code:-1 userInfo:@{NSLocalizedDescriptionKey : @"Trying to load a nil url"}];
completedBlock(nil, error, SDImageCacheTypeNone, url);
}
});
} url 不存在情况比较简单，移除加载圈，如果有回调，则回到一些错误信息等。
url 存在的情况：
if ([self sd_showActivityIndicatorView]) {
[self sd_addActivityIndicator];
}
这需要使用者自己设置，是否在加载时显示加载圈。
下面需要先分析SDWebImageManager
+ (nonnull instancetype)sharedManager {
static dispatch_once_t once;
static id instance;
dispatch_once(&once, ^{
instance = [self new];
});
return instance;
}
- (nonnull instancetype)init {
SDImageCache *cache = [SDImageCache sharedImageCache];
SDWebImageDownloader *downloader = [SDWebImageDownloader sharedDownloader];
return [self initWithCache:cache downloader:downloader];
}上述内容主要是UI显示层的操作，这里可以说是开始进入了SDWebImage的核心部分。
在sharedManager 中主要是完成了缓存类和下载类的初始化，及一些容器初始化
- (nonnull instancetype)initWithCache:(nonnull SDImageCache *)cache downloader:(nonnull SDWebImageDownloader *)downloader {
if ((self = [super init])) {
_imageCache = cache;
_imageDownloader = downloader;
_failedURLs = [NSMutableSet new]; // 不会重复存储
_runningOperations = [NSMutableArray new];
}
return self;
}在这里先持有cache和downloader,并创建了一个存储失败URL 的容器 _failedURLs 和一个存储正在运行的线程数组 _runningOperations。
先查看SDImageCache 的实现
+ (nonnull instancetype)sharedImageCache {
static dispatch_once_t once;
static id instance;
dispatch_once(&once, ^{
instance = [self new];
});
return instance;
}
- (instancetype)init {
return [self initWithNamespace:@"default"];
}
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns {
NSString *path = [self makeDiskCachePath:ns];
return [self initWithNamespace:ns diskCacheDirectory:path];
}
- (nullable NSString *)makeDiskCachePath:(nonnull NSString*)fullNamespace {
NSArray<NSString *> *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
return [paths[0] stringByAppendingPathComponent:fullNamespace];
}首先是在Disk 中创建了一个default的存储空间（就是创建了一个缓存文件存储路径）
- (nonnull instancetype)initWithNamespace:(nonnull NSString *)ns
diskCacheDirectory:(nonnull NSString *)directory {
if ((self = [super init])) {
NSString *fullNamespace = [@"com.hackemist.SDWebImageCache." stringByAppendingString:ns];
// Create IO serial queue
_ioQueue = dispatch_queue_create("com.hackemist.SDWebImageCache", DISPATCH_QUEUE_SERIAL);
_config = [[SDImageCacheConfig alloc] init];
// Init the memory cache
_memCache = [[AutoPurgeCache alloc] init];
_memCache.name = fullNamespace;
// Init the disk cache
if (directory != nil) {
_diskCachePath = [directory stringByAppendingPathComponent:fullNamespace];
} else {
NSString *path = [self makeDiskCachePath:ns];
_diskCachePath = path;
}
dispatch_sync(_ioQueue, ^{
_fileManager = [NSFileManager new];
});
#if SD_UIKIT
// Subscribe to app events
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(clearMemory)
name:UIApplicationDidReceiveMemoryWarningNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(deleteOldFiles)
name:UIApplicationWillTerminateNotification
object:nil];
[[NSNotificationCenter defaultCenter] addObserver:self
selector:@selector(backgroundDeleteOldFiles)
name:UIApplicationDidEnterBackgroundNotification
object:nil];
#endif
}
return self;
}SDImageCacheConfig类是对缓存做配置，是否解码，存储周期等信息
AutoPurgeCache类 只是实现了一个监听UIApplicationDidReceiveMemoryWarningNotification 内存报警时，移除全部。
实现文件管理后再添加监听
UIApplicationDidReceiveMemoryWarningNotification 执行方法clearMemory
UIApplicationWillTerminateNotification 执行方法deleteOldFiles
UIApplicationDidEnterBackgroundNotification 执行方法backgroundDeleteOldFiles
- (void)clearMemory {
[self.memCache removeAllObjects];
}可见当收到内存警告时，直接将缓存的全部内容清空
- (void)deleteOldFiles {
[self deleteOldFilesWithCompletionBlock:nil];
}
- (void)deleteOldFilesWithCompletionBlock:(nullable SDWebImageNoParamsBlock)completionBlock {
dispatch_async(self.ioQueue, ^{
NSURL *diskCacheURL = [NSURL fileURLWithPath:self.diskCachePath isDirectory:YES];
NSArray<NSString *> *resourceKeys = @[NSURLIsDirectoryKey, NSURLContentModificationDateKey, NSURLTotalFileAllocatedSizeKey];
// This enumerator prefetches useful properties for our cache files.
NSDirectoryEnumerator *fileEnumerator = [_fileManager enumeratorAtURL:diskCacheURL
includingPropertiesForKeys:resourceKeys
options:NSDirectoryEnumerationSkipsHiddenFiles
errorHandler:NULL];
NSDate *expirationDate = [NSDate dateWithTimeIntervalSinceNow:-self.config.maxCacheAge];
NSMutableDictionary<NSURL *, NSDictionary<NSString *, id> *> *cacheFiles = [NSMutableDictionary dictionary];
NSUInteger currentCacheSize = 0;
// Enumerate all of the files in the cache directory. This loop has two purposes:
//
// 1. Removing files that are older than the expiration date.
// 2. Storing file attributes for the size-based cleanup pass.
NSMutableArray<NSURL *> *urlsToDelete = [[NSMutableArray alloc] init];
for (NSURL *fileURL in fileEnumerator) {
NSError *error;
NSDictionary<NSString *, id> *resourceValues = [fileURL resourceValuesForKeys:resourceKeys error:&error];
// Skip directories and errors.
if (error || !resourceValues || [resourceValues[NSURLIsDirectoryKey] boolValue]) {
continue;
}
// Remove files that are older than the expiration date;
NSDate *modificationDate = resourceValues[NSURLContentModificationDateKey];
if ([[modificationDate laterDate:expirationDate] isEqualToDate:expirationDate]) {
[urlsToDelete addObject:fileURL];
continue;
}
// Store a reference to this file and account for its total size.
NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
currentCacheSize += totalAllocatedSize.unsignedIntegerValue;
cacheFiles[fileURL] = resourceValues;
}
for (NSURL *fileURL in urlsToDelete) {
[_fileManager removeItemAtURL:fileURL error:nil];
}
// If our remaining disk cache exceeds a configured maximum size, perform a second
// size-based cleanup pass. We delete the oldest files first.
if (self.config.maxCacheSize > 0 && currentCacheSize > self.config.maxCacheSize) {
// Target half of our maximum cache size for this cleanup pass.
const NSUInteger desiredCacheSize = self.config.maxCacheSize / 2;
// Sort the remaining cache files by their last modification time (oldest first).
NSArray<NSURL *> *sortedFiles = [cacheFiles keysSortedByValueWithOptions:NSSortConcurrent
usingComparator:^NSComparisonResult(id obj1, id obj2) {
return [obj1[NSURLContentModificationDateKey] compare:obj2[NSURLContentModificationDateKey]];
}];
// Delete files until we fall below our desired cache size.
for (NSURL *fileURL in sortedFiles) {
if ([_fileManager removeItemAtURL:fileURL error:nil]) {
NSDictionary<NSString *, id> *resourceValues = cacheFiles[fileURL];
NSNumber *totalAllocatedSize = resourceValues[NSURLTotalFileAllocatedSizeKey];
currentCacheSize -= totalAllocatedSize.unsignedIntegerValue;
if (currentCacheSize < desiredCacheSize) {
break;
}
}
}
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock();
});
}
});
}当程序进入后台和程序结束时执行上述方法。略有差别的是，当程序进入后台会申请时间处理清理过程。
具体清理策略是，先清理已过期的文件，如果设置了最大缓存空间（默认没设置，等于0），当超出缓存空间时间，先将缓存内容按时间排序，从最久远的时间开始删除，一致删到 安全空间值（最大缓存空间的一半）
下篇分析 SDWebImageDownloader