在iOS开发过程中经常需要通过网络请求加载图片，有时，需要在创建UIImageView或UIButton来显示图片之前需要提前知道图片的尺寸，根据图片尺寸创建对应大小的控件。但是对于网络图片来说，要想通过最优的方法获得尺寸就略微有点困难，大体思路有这么几种：
1.通过服务器处理。即在下行图片路径时拼接该图片的宽高。这种方法最简单，避免了不必要的网络请求，只需要从URL中截取即可。
2.网络请求。先通过文件头获取图片大小，如果获取失败，则下载完整的图片data，然后计算大小；如果有使用SDWebImage，则首先检查是否缓存过该图片，下面针对格式为png、fig、jpg文件获取其尺寸大小，直接上代码：
首先宏定义一个单例实现
// @interface
#define singleton_interface(className) \
+ (className *)shared##className;
// @implementation
#define singleton_implementation(className) \
static className *_instance; \
+ (id)allocWithZone:(NSZone *)zone \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [super allocWithZone:zone]; \
}); \
return _instance; \
} \
+ (className *)shared##className \
{ \
static dispatch_once_t onceToken; \
dispatch_once(&onceToken, ^{ \
_instance = [[self alloc] init]; \
}); \
return _instance; \
}
********************************************************************
然后头文件如下
#import <Foundation/Foundation.h>
#import "Singleton.h"
@interface BLImageSize : NSObject
singleton_interface(BLImageSize)
/**
获取网络图片的Size, 先通过文件头来获取图片大小
如果失败 会下载完整的图片Data 来计算大小 所以最好别放在主线程
如果你有使用SDWebImage就会先看下 SDWebImage有缓存过改图片没有
支持文件头大小的格式 png、gif、jpg
*/
+(CGSize)downloadImageSizeWithURL:(id)imageURL;
@end
*************************************************************************
最后是.m文件实现
#import "BLImageSize.h"
#import "SDImageCache.h"
@implementation BLImageSize
singleton_implementation(BLImageSize)
+(CGSize)downloadImageSizeWithURL:(id)imageURL
{
NSURL* URL = nil;
if([imageURL isKindOfClass:[NSURL class]]){
URL = imageURL;
}
if([imageURL isKindOfClass:[NSString class]]){
URL = [NSURL URLWithString:imageURL];
}
if(URL == nil)
return CGSizeZero;
NSString* absoluteString = URL.absoluteString;
#ifdef dispatch_main_sync_safe
if([[SDImageCache sharedImageCache] diskImageExistsWithKey:absoluteString])
{
UIImage* image = [[SDImageCache sharedImageCache] imageFromMemoryCacheForKey:absoluteString];
if(!image)
{
NSData* data = [[SDImageCache sharedImageCache] performSelector:@selector(diskImageDataBySearchingAllPathsForKey:) withObject:URL.absoluteString];
image = [UIImage imageWithData:data];
}
if(image)
{
return image.size;
}
}
#endif
NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:URL];
NSString* pathExtendsion = [URL.pathExtension lowercaseString];
CGSize size = CGSizeZero;
if([pathExtendsion isEqualToString:@"png"]){
size = [self downloadPNGImageSizeWithRequest:request];
}
else if([pathExtendsion isEqual:@"gif"])
{
size = [self downloadGIFImageSizeWithRequest:request];
}
else{
size = [self downloadJPGImageSizeWithRequest:request];
}
if(CGSizeEqualToSize(CGSizeZero, size))
{
NSData* data = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:URL] returningResponse:nil error:nil];
UIImage* image = [UIImage imageWithData:data];
if(image)
{
#ifdef dispatch_main_sync_safe
[[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:YES imageData:data forKey:URL.absoluteString toDisk:YES];
#endif
size = image.size;
}
}
return size;
}
+(CGSize)downloadPNGImageSizeWithRequest:(NSMutableURLRequest*)request
{
[request setValue:@"bytes=16-23" forHTTPHeaderField:@"Range"];
NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
if(data.length == 8)
{
int w1 = 0, w2 = 0, w3 = 0, w4 = 0;
[data getBytes:&w1 range:NSMakeRange(0, 1)];
[data getBytes:&w2 range:NSMakeRange(1, 1)];
[data getBytes:&w3 range:NSMakeRange(2, 1)];
[data getBytes:&w4 range:NSMakeRange(3, 1)];
int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;
int h1 = 0, h2 = 0, h3 = 0, h4 = 0;
[data getBytes:&h1 range:NSMakeRange(4, 1)];
[data getBytes:&h2 range:NSMakeRange(5, 1)];
[data getBytes:&h3 range:NSMakeRange(6, 1)];
[data getBytes:&h4 range:NSMakeRange(7, 1)];
int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + h4;
return CGSizeMake(w, h);
}
return CGSizeZero;
}
+(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request
{
[request setValue:@"bytes=6-9" forHTTPHeaderField:@"Range"];
NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
if(data.length == 4)
{
short w1 = 0, w2 = 0;
[data getBytes:&w1 range:NSMakeRange(0, 1)];
[data getBytes:&w2 range:NSMakeRange(1, 1)];
short w = w1 + (w2 << 8);
short h1 = 0, h2 = 0;
[data getBytes:&h1 range:NSMakeRange(2, 1)];
[data getBytes:&h2 range:NSMakeRange(3, 1)];
short h = h1 + (h2 << 8);
return CGSizeMake(w, h);
}
return CGSizeZero;
}
+(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request
{
[request setValue:@"bytes=0-209" forHTTPHeaderField:@"Range"];
NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
if ([data length] <= 0x58) {
return CGSizeZero;
}
if ([data length] < 210) {// 肯定只有一个DQT字段
short w1 = 0, w2 = 0;
[data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];
[data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];
short w = (w1 << 8) + w2;
short h1 = 0, h2 = 0;
[data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];
[data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];
short h = (h1 << 8) + h2;
return CGSizeMake(w, h);
} else {
short word = 0x0;
[data getBytes:&word range:NSMakeRange(0x15, 0x1)];
if (word == 0xdb) {
[data getBytes:&word range:NSMakeRange(0x5a, 0x1)];
if (word == 0xdb) {// 两个DQT字段
short w1 = 0, w2 = 0;
[data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];
[data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];
short w = (w1 << 8) + w2;
short h1 = 0, h2 = 0;
[data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];
[data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];
short h = (h1 << 8) + h2;
return CGSizeMake(w, h);
} else {// 一个DQT字段
short w1 = 0, w2 = 0;
[data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];
[data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];
short w = (w1 << 8) + w2;
short h1 = 0, h2 = 0;
[data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];
[data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];
short h = (h1 << 8) + h2;
return CGSizeMake(w, h);
}
} else {
return CGSizeZero;
}
}
}
@end |
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