###结合 SDWebImage 修改图片显示效果
原理 method swizzling 实际上就是一种在运行时动态修改原有方法的技术, 它实际上是基于ObjC runtime的特性, 而 method swizzling 的核心方法就是 method_exchangeImplementations(SEL origin, SEL swizzle)使用这个方法就可以在运行时动态地改变原有的方法实现。
+ (void)load {
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
Class class = [self class];
SEL originalSelector = @selector(sd_setImageWithURL:placeholderImage:);
SEL swizzledSelector = @selector(sd_fadeSetImageWithURL:placeholderImage:);
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
BOOL success = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
if (success) {
class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
}else {
method_exchangeImplementations(originalMethod, swizzledMethod);
}
});
}
- (void)sd_fadeSetImageWithURL:(NSURL *)url placeholderImage:(UIImage *)placeholder {
__weak typeof(self) weakSelf = self;
[self sd_setImageWithURL:url placeholderImage:placeholder options:SDWebImageAvoidAutoSetImage completed:^(UIImage * _Nullable image, NSError * _Nullable error, SDImageCacheType cacheType, NSURL * _Nullable imageURL) {
if (!weakSelf || error) {
return ;
}
weakSelf.image = image;
if (image || cacheType == SDImageCacheTypeNone) {
CATransition *transition = [CATransition animation];
transition.duration = 1;
transition.type = kCATransitionFade;
transition.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseInEaseOut];
[self.layer addAnimation:transition forKey:nil];
}
[weakSelf setNeedsLayout];
}];
}