SDWebImage有一个SDWebImageDownloaderOperation类来执行下载操作的。里面有个下载完成的方法：
- (void)connectionDidFinishLoading:(NSURLConnection *)aConnection {
SDWebImageDownloaderCompletedBlock completionBlock = self.completedBlock;
@synchronized(self) {
CFRunLoopStop(CFRunLoopGetCurrent());
self.thread = nil;
self.connection = nil;
[[NSNotificationCenter defaultCenter] postNotificationName:SDWebImageDownloadStopNotification object:nil];
}
if (![[NSURLCache sharedURLCache] cachedResponseForRequest:_request]) {
responseFromCached = NO;
}
if (completionBlock)
{
if (self.options & SDWebImageDownloaderIgnoreCachedResponse && responseFromCached) {
completionBlock(nil, nil, nil, YES);
}
else {
UIImage *image = [UIImage sd_imageWithData:self.imageData];
NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:self.request.URL];
image = [self scaledImageForKey:key image:image];
// Do not force decoding animated GIFs
if (!image.images) {
image = [UIImage decodedImageWithImage:image];
}
if (CGSizeEqualToSize(image.size, CGSizeZero)) {
completionBlock(nil, nil, [NSError errorWithDomain:@"SDWebImageErrorDomain" code:0 userInfo:@{NSLocalizedDescriptionKey : @"Downloaded image has 0 pixels"}], YES);
}
else {
completionBlock(image, self.imageData, nil, YES);
}
}
}
self.completionBlock = nil;
[self done];
}
其中，UIImage *image = [UIImage sd_imageWithData:self.imageData];就是将data转换成image。
再看看sd_imageWithData:这个方法：
+ (UIImage *)sd_imageWithData:(NSData *)data {
UIImage *image;
NSString *imageContentType = [NSData sd_contentTypeForImageData:data];
if ([imageContentType isEqualToString:@"image/gif"]) {
image = [UIImage sd_animatedGIFWithData:data];
}
#ifdef SD_WEBP
else if ([imageContentType isEqualToString:@"image/webp"])
{
image = [UIImage sd_imageWithWebPData:data];
}
#endif
else {
image = [[UIImage alloc] initWithData:data];
UIImageOrientation orientation = [self sd_imageOrientationFromImageData:data];
if (orientation != UIImageOrientationUp) {
image = [UIImage imageWithCGImage:image.CGImage
scale:image.scale
orientation:orientation];
}
}
return image;
}
这个方法在UIImage+MultiFormat里面，是UIImage的一个类别处理。这句话很重要image = [[UIImage alloc] initWithData:data]; SDWebImage把下载下来的data直接转成image，然后没做等比缩放直接存起来使用。所以，我们只需要在这边做处理即可：
UIImage+MultiFormat添加一个方法：
+(UIImage *)compressImageWith:(UIImage *)image
{
float imageWidth = image.size.width;
float imageHeight = image.size.height;
float width = 640;
float height = image.size.height/(image.size.width/width);
float widthScale = imageWidth /width;
float heightScale = imageHeight /height;
// 创建一个bitmap的context
// 并把它设置成为当前正在使用的context
UIGraphicsBeginImageContext(CGSizeMake(width, height));
if (widthScale > heightScale) {
[image drawInRect:CGRectMake(0, 0, imageWidth /heightScale , height)];
}
else {
[image drawInRect:CGRectMake(0, 0, width , imageHeight /widthScale)];
}
// 从当前context中创建一个改变大小后的图片
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
// 使当前的context出堆栈
UIGraphicsEndImageContext();
return newImage;
}
然后在：image = [[UIImage alloc] initWithData:data];下面调用以下：
if (data.length/1024 > 1024) {
image = [self compressImageWith:image];
}
当data大于1M的时候做压缩处理。革命尚未成功，还需要一步处理。在SDWebImageDownloaderOperation的connectionDidFinishLoading方法里面的：
UIImage *image = [UIImage sd_imageWithData:self.imageData];
//将等比压缩过的image在赋在转成data赋给self.imageData
NSData *data = UIImageJPEGRepresentation(image, 1);
self.imageData = [NSMutableData dataWithData:data];
修改好之后的代码
#import "UIImage+MultiFormat.h"
#import "UIImage+GIF.h"
#import "NSData+ImageContentType.h"
#import <ImageIO/ImageIO.h>
#ifdef SD_WEBP
#import "UIImage+WebP.h"
#endif
@implementation UIImage (MultiFormat)
+ (UIImage *)sd_imageWithData:(NSData *)data {
UIImage *image;
NSString *imageContentType = [NSData sd_contentTypeForImageData:data];
if ([imageContentType isEqualToString:@"image/gif"]) {
image = [UIImage sd_animatedGIFWithData:data];
}
#ifdef SD_WEBP
else if ([imageContentType isEqualToString:@"image/webp"])
{
image = [UIImage sd_imageWithWebPData:data];
}
#endif
else {
image = [[UIImage alloc] initWithData:data];
if (data.length/1024 > 100) {
image = [self compressImageWith:image];
}
UIImageOrientation orientation = [self sd_imageOrientationFromImageData:data];
if (orientation != UIImageOrientationUp) {
image = [UIImage imageWithCGImage:image.CGImage
scale:image.scale
orientation:orientation];
}
}
return image;
}
+(UIImage *)compressImageWith:(UIImage *)image
{
float imageWidth = image.size.width;
float imageHeight = image.size.height;
float width = 750;
float height = image.size.height/(image.size.width/width);
float widthScale = imageWidth /width;
float heightScale = imageHeight /height;
UIGraphicsBeginImageContext(CGSizeMake(width, height));
if (widthScale > heightScale) {
[image drawInRect:CGRectMake(0, 0, imageWidth /heightScale , height)];
}
else {
[image drawInRect:CGRectMake(0, 0, width , imageHeight /widthScale)];
}
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
+(UIImageOrientation)sd_imageOrientationFromImageData:(NSData *)imageData {
UIImageOrientation result = UIImageOrientationUp;
CGImageSourceRef imageSource = CGImageSourceCreateWithData((__bridge CFDataRef)imageData, NULL);
if (imageSource) {
CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, NULL);
if (properties) {
CFTypeRef val;
int exifOrientation;
val = CFDictionaryGetValue(properties, kCGImagePropertyOrientation);
if (val) {
CFNumberGetValue(val, kCFNumberIntType, &exifOrientation);
result = [self sd_exifOrientationToiOSOrientation:exifOrientation];
} // else - if it's not set it remains at up
CFRelease((CFTypeRef) properties);
} else {
}
CFRelease(imageSource);
}
return result;
}
#pragma mark EXIF orientation tag converter
// Convert an EXIF image orientation to an iOS one.
// reference see here: http://sylvana.net/jpegcrop/exif_orientation.html
+ (UIImageOrientation) sd_exifOrientationToiOSOrientation:(int)exifOrientation {
UIImageOrientation orientation = UIImageOrientationUp;
switch (exifOrientation) {
case 1:
orientation = UIImageOrientationUp;
break;
case 3:
orientation = UIImageOrientationDown;
break;
case 8:
orientation = UIImageOrientationLeft;
break;
case 6:
orientation = UIImageOrientationRight;
break;
case 2:
orientation = UIImageOrientationUpMirrored;
break;
case 4:
orientation = UIImageOrientationDownMirrored;
break;
case 5:
orientation = UIImageOrientationLeftMirrored;
break;
case 7:
orientation = UIImageOrientationRightMirrored;
break;
default:
break;
}
return orientation;
}
@end
