应用场景，屏幕上只有一个Imageview，你只有一堆图片的url地址。需求：有个按钮点了以后，要快速切换到下一张图片。
这时候用SDWebImage的”UImageView+WebCache”是不是感觉有点捉急了，他TM还要一张张的加载。这里我们要的效果是，我在看某张图片的时候，后面的几张也给我TM加载好，就算没有加载好，我切过去的时候也给我显示一个进度条啊。
我的ImageDownloader的思路是：
1、既然有一组url地址，那就先给我吧，我直接去开始加载了。针对每个operation，加载完后就把value:图片 key:url地址 存到我这个singleton的NSCache里
- (void)startDownloadImagesWithURLArray:(NSArray *)urlstrArray
{
for (NSString *str in urlstrArray) {
if (str.length > 0) {
[self enqueueOperationWithStr:str];
}
}
}
- (void)enqueueOperationWithStr:(NSString *)str
{
NSMutableURLRequest *req = [[NSMutableURLRequest alloc] initWithURL:[NSURL URLWithString:str] cachePolicy:NSURLCacheStorageAllowed timeoutInterval:8.0];
ILSMLWebImageDownloaderOperation *op = [[ILSMLWebImageDownloaderOperation alloc] initWithRequest:req queue:self.workingQueue];
[self.downloadQueue addOperation:op];
op.completedBlock = ^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
if (!error) {
MYLog(@"ILSMLImageDownloader is cache image for url %@", str);
[self.dlCache setObject:image forKey:str];
}else {
MYLog(@"ILSMLWebImageDownloaderOperation download image error occured %@", error);
}
};
if (!self.blocksDic[str]) {
self.blocksDic[str] = op;
}
}
2、外部接口就提供，你直接根据你的url地址来获取我这个singleton里cache的图片吧，如果我还没cache吧，那么我就告诉你，我现在的进度progressBlock，另外，一但我加载完，我也会告诉你的哦，compeletionBlock
- (UIImage *)imageForUrl:(NSString *)imageURLStr progressBlock:(SDWebImageDownloaderProgressBlock)progressBlock compeletionBlock:(SDWebImageDownloaderCompletedBlock)compeletionBlock
{
UIImage *cacheImage = [self.dlCache objectForKey:imageURLStr];
if (!cacheImage) {
ILSMLWebImageDownloaderOperation *op = self.blocksDic[imageURLStr];
if (op) {
if (progressBlock) {
op.progressBlock = ^(NSUInteger receivedSize, long long expectedSize) {
progressBlock(receivedSize, expectedSize);
};
}
if (compeletionBlock) {
op.completedBlock = ^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
if (!error) {
[self.dlCache setObject:image forKey:imageURLStr];
}
compeletionBlock(image, data, error, finished);
};
}
}else {
MYLog(@"ILSMLImageDownloader operation block does not exist");
}
}
return cacheImage;
}
3、做男人当然要做一个有责任心的男人，既然你和它没关系了，那let it free吧。所以第三个接口就是清理掉不用的image
- (void)removeImageWithURLStr:(NSString *)imageURLStr
{
ILSMLWebImageDownloaderOperation *op = self.blocksDic[imageURLStr];
[op cancel];
[self.blocksDic removeObjectForKey:imageURLStr];
[self.dlCache removeObjectForKey:imageURLStr];
}
具体的使用例子：
- (void)loadImageData
{
if (self.mediaDicArray.count == 0) {
[[ILSINSNewInsatgramApi sharedInstance] otherUserDownloadMeidaWithCursor:self.currentCusor
userId:@"203560" compeletionHandler:^(NSArray *mediaDicArray, NSString *nextCusor, NSError *error)
{
if (!error) {
[self.mediaDicArray addObjectsFromArray:mediaDicArray];
NSMutableArray *mArray = [NSMutableArray arrayWithCapacity:mediaDicArray.count];
for (id obj in mediaDicArray) {
[mArray addObject:[obj valueForKeyPath:@"images.low_resolution.url"]];
}
[[ILSMLImageDownloader sharedDownloader] startDownloadImagesWithURLArray:mArray];
self.currentCusor = nextCusor;
[self customImage];
}
}];
}else {
[self customImage];
}
}
- (void)customImage
{
NSString *path = [self.mediaDicArray[0] valueForKeyPath:@"images.low_resolution.url"];
UIImage *result = [[ILSMLImageDownloader sharedDownloader] imageForUrl:path progressBlock:^(NSUInteger receivedSize, long long expectedSize) {
MYLog(@"-----ILSMLEarnCoinsViewController is loading is %d total is %llu", receivedSize, expectedSize);
} compeletionBlock:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
MYLog(@"-----ILSMLEarnCoinsViewController is compeletion");
self.currentImageView.image = image;
}];
self.currentImageView.image = result;
}
- (void)skip:(id)sender
{
if (self.mediaDicArray.count > 0) {
NSString *path = [self.mediaDicArray[0] valueForKeyPath:@"images.low_resolution.url"];
[[ILSMLImageDownloader sharedDownloader] removeImageWithURLStr:path];
[self.mediaDicArray removeObjectAtIndex:0];
}
[self loadImageData];
}
记录一下最近吧，昨天早上被指派了一个新项目，自己iOS端逻辑今天全弄好了（过段时间整理下Instagram objc的API，open source出来），下午贴图。再过几天，等服务器端同事接口写好，我再花个两天，测试再花个几天，下周估计就能上线了。这个鸡巴项目叫morelikers。我们app扮演了一个”拉皮条“的角色。
下下周，中秋， lonely alone 去北京感受一下。