网上的思路基本就是把下载的图片进行压缩，但是我这边遇到点问题，一个是网上的基本是老版本的SDWebImage，我用的5.0.0的不太适用，再一个就是用的pod,直接在源码更改不太理想。
我这边的解决思路就是找到SDWebImage下载图片的方法对下载完的图片进行压缩，当然实现方式使用runtime的swizzledSelector，这样不用改动源码。
SDWebImage下载图片的方法
网上查了一些关于SDWebImage(5.0.0)源码解析的资料，最后基本定位在这个两个方法
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
- (void)callCompletionBlocksWithImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
error:(nullable NSError *)error
finished:(BOOL)finished
hook一个类中的实例方法
这里贴一下代码
+ (void)swizzlingInClass:(Class)cls originalSelector:(SEL)originalSelector swizzledSelector:(SEL)swizzledSelector
{
Class class = cls;
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
if (!originalMethod || !swizzledMethod) {
return;
}
IMP originalIMP = method_getImplementation(originalMethod);
IMP swizzledIMP = method_getImplementation(swizzledMethod);
const char *originalType = method_getTypeEncoding(originalMethod);
const char *swizzledType = method_getTypeEncoding(swizzledMethod);
class_replaceMethod(class,swizzledSelector,originalIMP,originalType);
class_replaceMethod(class,originalSelector,swizzledIMP,swizzledType);
}
这里是具体实现
创建SDWebImageDownloaderOperation一个分类做hook，代码供参考
#import "SDWebImageDownloaderOperation.h"
NS_ASSUME_NONNULL_BEGIN
@interface SDWebImageDownloaderOperation (HDImageCompressHook)
@end
NS_ASSUME_NONNULL_END
#import "SDWebImageDownloaderOperation+HDImageCompressHook.h"
#import "HDBJHookTool.h"
@implementation SDWebImageDownloaderOperation (HDImageCompressHook)
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
SEL originalSelector1 = @selector(URLSession: task: didCompleteWithError:);
SEL swizzledSelector1 = @selector(hd_URLSession: task: didCompleteWithError:);
[HDBJHookTool swizzlingInClass:[self class] originalSelector:originalSelector1 swizzledSelector:swizzledSelector1];
[HDBJHookTool swizzlingInClass:[self class] originalSelector:originalSelector1 swizzledSelector:swizzledSelector1];
SEL originalSelector2 = @selector(callCompletionBlocksWithImage:
imageData:
error:
finished:);
SEL swizzledSelector2 = @selector(hd_callCompletionBlocksWithImage:
imageData:
error:
finished:);
[HDBJHookTool swizzlingInClass:[self class] originalSelector:originalSelector2 swizzledSelector:swizzledSelector2];
});
}
#pragma mark - Method Swizzling
- (void)hd_URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error{
Ivar ivar1 = class_getInstanceVariable([self class], "_imageData");
if (object_getIvar(self, ivar1)) {
NSMutableData * imageData = (NSMutableData *)object_getIvar(self, ivar1);
NSData *imgData = UIImageJPEGRepresentation([UIImage imageWithData:[imageData copy]],1);
NSUInteger sizeOriginKB = imageData.length / 1024;
if (sizeOriginKB > 500){
imgData = UIImageJPEGRepresentation([UIImage imageWithData:[imageData copy]],0.1);
[[SDImageCache sharedImageCache] setValue:nil forKey:@"memCache"];
}
// imgData = [self resetSizeOfImageData:[UIImage imageWithData:[imageData copy]] maxSize:50];
if (imgData.length/1024 > 200) {
UIImage *image = [self compressImageWith:[UIImage imageWithData:imgData]];
imgData = UIImagePNGRepresentation(image);
MyLog(@"didCompleteWithError---------%ld",imgData.length/1024);
if (imgData.length/1024 > 200) {
imageData = [NSMutableData dataWithData:[self resetSizeOfImageData:image maxSize:90]];
MyLog(@"didCompleteWithErrorresetSizeOfImageData---------%ld",imageData.length/1024);
}
}
imageData = [NSMutableData dataWithData:imgData];
object_setIvar(self, ivar1, imageData);
}
[self hd_URLSession:session task:task didCompleteWithError:error];
}
- (void)hd_callCompletionBlocksWithImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
error:(nullable NSError *)error
finished:(BOOL)finished{
NSUInteger sizeOriginKB = imageData.length / 1024;
if (sizeOriginKB > 500){
imageData = UIImageJPEGRepresentation(image,0.1);
image = [UIImage imageWithData:imageData];
}
// imageData = [self resetSizeOfImageData:image maxSize:90];
image = [UIImage imageWithData:imageData];
if (imageData.length/1024 > 200) {
image = [self compressImageWith:image];
imageData = UIImagePNGRepresentation(image);
MyLog(@"hd_callCompletionBlocksWithImage---------%ld",imageData.length/1024);
if (imageData.length/1024 > 200) {
imageData = [self resetSizeOfImageData:image maxSize:90];
image = [UIImage imageWithData:imageData];
MyLog(@"hd_callCompletionBlocksWithImageresetSizeOfImageData---------%ld",imageData.length/1024);
}
}
[self hd_callCompletionBlocksWithImage:image
imageData:imageData
error:error
finished:finished];
}
-(UIImage *)compressImageWith:(UIImage *)image{
float imageWidth = image.size.width;
float imageHeight = image.size.height;
float width = 320;
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;
}
#pragma mark - 图片压缩
- (NSData *)resetSizeOfImageData:(UIImage *)sourceImage maxSize:(NSInteger)maxSize {
//先判断当前质量是否满足要求，不满足再进行压缩
__block NSData *finallImageData = UIImageJPEGRepresentation(sourceImage,1.0);
NSUInteger sizeOrigin = finallImageData.length;
NSUInteger sizeOriginKB = sizeOrigin / 1024;
if (sizeOriginKB <= maxSize) {
return finallImageData;
}
//获取原图片宽高比
CGFloat sourceImageAspectRatio = sourceImage.size.width/sourceImage.size.height;
//先调整分辨率
CGSize defaultSize = CGSizeMake(1024, 1024/sourceImageAspectRatio);
UIImage *newImage = [self newSizeImage:defaultSize image:sourceImage];
finallImageData = UIImageJPEGRepresentation(newImage,1.0);
//保存压缩系数
NSMutableArray *compressionQualityArr = [NSMutableArray array];
CGFloat avg = 1.0/250;
CGFloat value = avg;
for (int i = 250; i >= 1; i--) {
value = i*avg;
[compressionQualityArr addObject:@(value)];
}
/*
调整大小
说明：压缩系数数组compressionQualityArr是从大到小存储。
*/
//思路：使用二分法搜索
finallImageData = [self halfFuntion:compressionQualityArr image:newImage sourceData:finallImageData maxSize:maxSize];
//如果还是未能压缩到指定大小，则进行降分辨率
while (finallImageData.length == 0) {
//每次降100分辨率
CGFloat reduceWidth = 100.0;
CGFloat reduceHeight = 100.0/sourceImageAspectRatio;
if (defaultSize.width-reduceWidth <= 0 || defaultSize.height-reduceHeight <= 0) {
break;
}
defaultSize = CGSizeMake(defaultSize.width-reduceWidth, defaultSize.height-reduceHeight);
UIImage *image = [self newSizeImage:defaultSize
image:[UIImage imageWithData:UIImageJPEGRepresentation(newImage,[[compressionQualityArr lastObject] floatValue])]];
finallImageData = [self halfFuntion:compressionQualityArr image:image sourceData:UIImageJPEGRepresentation(image,1.0) maxSize:maxSize];
}
return finallImageData;
}
#pragma mark 调整图片分辨率/尺寸（等比例缩放）
- (UIImage *)newSizeImage:(CGSize)size image:(UIImage *)sourceImage {
CGSize newSize = CGSizeMake(sourceImage.size.width, sourceImage.size.height);
CGFloat tempHeight = newSize.height / size.height;
CGFloat tempWidth = newSize.width / size.width;
if (tempWidth > 1.0 && tempWidth > tempHeight) {
newSize = CGSizeMake(sourceImage.size.width / tempWidth, sourceImage.size.height / tempWidth);
} else if (tempHeight > 1.0 && tempWidth < tempHeight) {
newSize = CGSizeMake(sourceImage.size.width / tempHeight, sourceImage.size.height / tempHeight);
}
UIGraphicsBeginImageContext(newSize);
[sourceImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return newImage;
}
#pragma mark 二分法
- (NSData *)halfFuntion:(NSArray *)arr image:(UIImage *)image sourceData:(NSData *)finallImageData maxSize:(NSInteger)maxSize {
NSData *tempData = [NSData data];
NSUInteger start = 0;
NSUInteger end = arr.count - 1;
NSUInteger index = 0;
NSUInteger difference = NSIntegerMax;
while(start <= end) {
index = start + (end - start)/2;
finallImageData = UIImageJPEGRepresentation(image,[arr[index] floatValue]);
NSUInteger sizeOrigin = finallImageData.length;
NSUInteger sizeOriginKB = sizeOrigin / 1024;
// NSLog(@"当前降到的质量：%ld", (unsigned long)sizeOriginKB);
// NSLog(@"\nstart：%zd\nend：%zd\nindex：%zd\n压缩系数：%lf", start, end, (unsigned long)index, [arr[index] floatValue]);
if (sizeOriginKB > maxSize) {
start = index + 1;
} else if (sizeOriginKB < maxSize) {
if (maxSize-sizeOriginKB < difference) {
difference = maxSize-sizeOriginKB;
tempData = finallImageData;
}
if (index<=0) {
break;
}
end = index - 1;
} else {
break;
}
}
return tempData;
}
@end
主要的压缩图片代码是这里
NSUInteger sizeOriginKB = imageData.length / 1024;
if (sizeOriginKB > 500){
imageData = UIImageJPEGRepresentation(image,0.1);
image = [UIImage imageWithData:imageData];
}
// imageData = [self resetSizeOfImageData:image maxSize:90];
image = [UIImage imageWithData:imageData];
if (imageData.length/1024 > 200) {
image = [self compressImageWith:image];
imageData = UIImagePNGRepresentation(image);
MyLog(@"hd_callCompletionBlocksWithImage---------%ld",imageData.length/1024);
if (imageData.length/1024 > 200) {
imageData = [self resetSizeOfImageData:image maxSize:90];
image = [UIImage imageWithData:imageData];
MyLog(@"hd_callCompletionBlocksWithImageresetSizeOfImageData---------%ld",imageData.length/1024);
}
}
这些压缩图片的方法是网上找的，在使用- (NSData *)resetSizeOfImageData:(UIImage *)sourceImage maxSize:(NSInteger)maxSize 这个方法直接压缩比较大的图片时比较慢，最后使用了现在这种多级判断压缩图片来实现。
大概就是这么一个思路了谁有更好的方法也可提供一下。