工作三年了，都没写过博客，没想到第一篇居然在上写的。
最近工作不好找啊，写点博客聊以自慰吧。不吐槽了，开始上正题吧。
我们经常会遇到头像圆角问题，当然如果一个界面里就一个圆角的imageView，感觉也没必要优化。
简单粗暴代码如下：
imageView.layer.cornerRadius = CGRectGetWidth(imageView.bounds)/2;
imageView.layer.masksToBounds = YES;
但是当在一个tableView的每一个Cell中的imageView都要设置圆角的话，麻烦就来了。就会导致离屏渲染，让CPU处理它不擅长而GPU擅长的切图工作，让GPU等着渲染。一帧下来，CPU还没处理完，GPU只能不渲染了，这就引起了掉帧。滑动卡顿是必须的。
当然了，用GPU去切图就好了，所以最好的办法就是对image进行处理，切圆角。我用了一个image的category添加一个方法处理图片圆角
@interface UIImage (WebRadius)
- (UIImage*)imageByRoundCornerRadius;
@end
@implementation UIImage (WebRadius)
- (UIImage*)imageByRoundCornerRadius{
UIGraphicsBeginImageContextWithOptions(self.size, NO, self.scale);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextScaleCTM(context, 1, -1);
CGContextTranslateCTM(context, 0, -self.size.height);
CGFloat minSize = MIN(self.size.width, self.size.height);
CGRect rect = CGRectMake((self.size.width-minSize)/2, (self.size.height-minSize)/2, minSize, minSize);
UIBezierPath * path = [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:minSize/2];
[path closePath];
CGContextSaveGState(context);
[path addClip];
CGContextDrawImage(context, rect, self.CGImage);
CGContextRestoreGState(context);
UIImage * image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
@end
图片只需要调用这个方法就可以进行image圆角处理。处理是在GPU中进行。（灵感来源于YYKit）
那么对于网络加载的图片该怎么处理？
我们很多人会使用SDWebImage进行网络请求图片，难道每次获取图片都要进行图片圆角化处理，然后显示吗？如果tableview一直滑动，那不是一直在圆角化处理吗？于是我想在SDWebImage从网络下载中对图片圆角化处理一下，然后保存在memory和disk中，再次从缓存中获取图片就不用圆角化处理了。SDWebImage在从网络下载图片成功后一般都会走SDImageCache的
storeImage:imageData:forKey:toDisk:completion:
方法进行保存。于是我使用了SDImageCache的category替换了storeImage:imageData:forKey:toDisk:completion:方法
代码如下：
@interface SDImageCache (WebRadius)
@property (nonatomic,retain)NSNumber * isCornerRadius;
@end
@implementation SDImageCache (WebRadius)
+ (void)load{
Method originalMethod = class_getInstanceMethod(self, @selector(storeImage:imageData:forKey:toDisk:completion:));
Method myMethod = class_getInstanceMethod(self, @selector(lh_storeImage:imageData:forKey:toDisk:completion:));
method_exchangeImplementations(originalMethod, myMethod);
}
static const char cornerRadiusKey = '\0';
- (void)setIsCornerRadius:(NSNumber *)isCornerRadius{
[self willChangeValueForKey:@"isCornerRadius"];
objc_setAssociatedObject(self, &cornerRadiusKey, isCornerRadius, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
[self didChangeValueForKey:@"isCornerRadius"];
}
- (NSNumber*)isCornerRadius{
return objc_getAssociatedObject(self, &cornerRadiusKey);
}
- (void)lh_storeImage:(nullable UIImage *)image
imageData:(nullable NSData *)imageData
forKey:(nullable NSString *)key
toDisk:(BOOL)toDisk
completion:(nullable SDWebImageNoParamsBlock)completionBlock
{
if (!image || !key) {
if (completionBlock) {
completionBlock();
}
return;
}
if ([self.isCornerRadius boolValue]) {
image = [image imageByRoundCornerRadius];
NSString * imageType = [self typeForImageData:imageData];
if ([imageType isEqualToString:@"image/jpeg"]) {
imageData = UIImageJPEGRepresentation(image, 1.0);
}
else if ([imageType isEqualToString:@"image/png"]){
imageData = UIImagePNGRepresentation(image);
}
}
Ivar memCachevar = class_getInstanceVariable([self class], [@"memCache" UTF8String]);
if (memCachevar == nil) {
memCachevar = class_getInstanceVariable([self class], [[NSString stringWithFormat:@"_%@",@"memCache"] UTF8String]);
}
NSCache * memCache = object_getIvar(self, memCachevar);
Ivar ioQueuevar = class_getInstanceVariable([self class], [@"ioQueue" UTF8String]);
if (ioQueuevar == nil) {
ioQueuevar = class_getInstanceVariable([self class], [[NSString stringWithFormat:@"_%@",@"ioQueue"] UTF8String]);
}
dispatch_queue_t ioQueue = object_getIvar(self, ioQueuevar);
if (self.config.shouldCacheImagesInMemory) {
NSUInteger cost = image.size.height * image.size.width * image.scale * image.scale;
[memCache setObject:image forKey:key cost:cost];
}
if (toDisk) {
dispatch_async(ioQueue, ^{
@autoreleasepool {
NSData *data = imageData;
if (!data && image) {
SDImageFormat imageFormatFromData = [NSData sd_imageFormatForImageData:data];
data = [image sd_imageDataAsFormat:imageFormatFromData];
}
[self storeImageDataToDisk:data forKey:key];
}
if (completionBlock) {
dispatch_async(dispatch_get_main_queue(), ^{
completionBlock();
});
}
});
}
else {
if (completionBlock) {
completionBlock();
}
}
}
- (NSString *)typeForImageData:(NSData *)data {
uint8_t c;
[data getBytes:&c length:1];
switch (c) {
case 0xFF:
return @"image/jpeg";
case 0x89:
return @"image/png";
case 0x47:
return @"image/gif";
case 0x49:
case 0x4D:
return @"image/tiff";
}
return nil;
}
其中isCornerRadius是是否圆角的判断。这样就可以在不修改SDWebImage源码的情况下进行图片圆角操作了。不过主程序就得这样写
[SDImageCache sharedImageCache].isCornerRadius = [NSNumber numberWithBool:YES];
UIImageView * imageView = [[UIImageView alloc] init];
imageView.backgroundColor = [UIColor clearColor];
NSString * urlString = @"http://www.cdhdky.com/images/ttt.jpg";
UIImage * image = [[SDImageCache sharedImageCache] imageFromCacheForKey:urlString];
if (image) {
imageView.frame = CGRectMake(0, 0, image.size.width, image.size.height);
imageView.center = self.view.center;
imageView.image = image;
}
else{
__weak __typeof(self) weakSelf = self;
[[SDWebImageManager sharedManager] loadImageWithURL:[NSURL URLWithString:urlString] options:SDWebImageRetryFailed progress:nil completed:^(UIImage * _Nullable image, NSData * _Nullable data, NSError * _Nullable error, SDImageCacheType cacheType, BOOL finished, NSURL * _Nullable imageURL) {
imageView.frame = CGRectMake(0, 0, image.size.width, image.size.height);
imageView.center = weakSelf.view.center;
imageView.image = [[SDImageCache sharedImageCache]imageFromCacheForKey:imageURL.absoluteString];
}];
}
[self.view addSubview:imageView];
本人有点懒，如果有什么不懂的请留言。这个category有点缺陷需要继续完善。从今天起，开始分享我的知识，虽然我很笨。
完整demo在github中。