自动适配多种尺寸占位图（带缓存）

#import "UIImage+Placeholder.h"

#import "MyCommon.h"

#define SCLoading @"SCLoading"

static NSMutableDictionary *mutableImageDic;

@implementation UIImage (Placeholder)

+ (UIImage *)loadingImage:(CGSize)size{

//初始化

if (!mutableImageDic) {

mutableImageDic = [NSMutableDictionary new];

[mutableImageDic setObject:[UIImage imageNamed:SCLoading] forKey:SCLoading];

}

if (CGSizeEqualToSize(size, CGSizeZero)) {//如果是自动布局没有size，则三倍面积

UIImage *img = (UIImage *)[mutableImageDic objectForKey:SCLoading];

size = CGSizeMake(img.size.width * 3, img.size.height * 3);

}

//如果缓存里面，马上返回

NSString *imageSizeKey = NSStringFromCGSize(size);

UIImage *cacheImage = [mutableImageDic objectForKey:imageSizeKey];

if (cacheImage) {

return cacheImage;

}

//没有就绘制

UIImage *img = [mutableImageDic objectForKey:SCLoading];

UIGraphicsBeginImageContextWithOptions(size, NO, [UIScreen mainScreen].scale);

CGContextRef context = UIGraphicsGetCurrentContext();

CGContextSetFillColorWithColor(context, UIColorFromRGB(0xDBDBDB).CGColor);

CGContextFillRect(context, CGRectMake(0, 0, size.width, size.height));

if (size.width < img.size.width || size.height < img.size.height) {

[img drawInRect:CGRectMake(0, 0, size.width, size.height)];

}else{

[img drawInRect:CGRectMake((size.width - img.size.width)/2, (size.height - img.size.height)/2, img.size.width, img.size.height)];

}

UIImage* retImage = UIGraphicsGetImageFromCurrentImageContext();

UIGraphicsEndImageContext();

//绘制后添加到到字典内

[mutableImageDic setObject:retImage forKey:imageSizeKey];

return retImage;

}

@end