获取网络图片的尺寸大小

来源：互联网发布：iphone4s刷机软件编辑：程序博客网时间：2024/06/04 19:00

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:[NSURLclass]]){

URL = imageURL;

}

if([imageURL isKindOfClass:[NSStringclass]]){

URL = [NSURLURLWithString:imageURL];

}

if(URL == nil)

return CGSizeZero;

NSString* absoluteString = URL.absoluteString;

#ifdef dispatch_main_sync_safe

if([[SDImageCachesharedImageCache] diskImageExistsWithKey:absoluteString])

{

UIImage* image = [[SDImageCachesharedImageCache] imageFromMemoryCacheForKey:absoluteString];

if(!image)

{

NSData* data = [[SDImageCachesharedImageCache] performSelector:@selector(diskImageDataBySearchingAllPathsForKey:)withObject:URL.absoluteString];

image = [UIImageimageWithData:data];

}

if(image)

{

return image.size;

}

#endif

NSMutableURLRequest *request = [[NSMutableURLRequestalloc] initWithURL:URL];

NSString* pathExtendsion = [URL.pathExtensionlowercaseString];

CGSize size = CGSizeZero;

if([pathExtendsion isEqualToString:@"png"]){

size = [selfdownloadPNGImageSizeWithRequest:request];

}

else if([pathExtendsionisEqual:@"gif"])

{

size = [selfdownloadGIFImageSizeWithRequest:request];

}

else{

size = [selfdownloadJPGImageSizeWithRequest:request];

}

if(CGSizeEqualToSize(CGSizeZero, size))

{

NSData* data = [NSURLConnectionsendSynchronousRequest:[NSURLRequestrequestWithURL:URL] returningResponse:nilerror:nil];

UIImage* image = [UIImageimageWithData:data];

if(image)

{

#ifdef dispatch_main_sync_safe

[[SDImageCachesharedImageCache] storeImage:imagerecalculateFromImage:YESimageData:data forKey:URL.absoluteStringtoDisk:YES];

#endif

size = image.size;

}

return size;

}

+(CGSize)downloadPNGImageSizeWithRequest:(NSMutableURLRequest*)request

{

[request setValue:@"bytes=16-23"forHTTPHeaderField:@"Range"];

NSData* data = [NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror:nil];

if(data.length ==8)

{

int w1 = 0, w2 =0, w3 = 0, w4 =0;

[datagetBytes:&w1 range:NSMakeRange(0,1)];

[datagetBytes:&w2 range:NSMakeRange(1,1)];

[datagetBytes:&w3 range:NSMakeRange(2,1)];

[datagetBytes:&w4 range:NSMakeRange(3,1)];

int w = (w1 << 24) + (w2 <<16) + (w3 << 8) + w4;

int h1 = 0, h2 =0, h3 = 0, h4 =0;

[datagetBytes:&h1 range:NSMakeRange(4,1)];

[datagetBytes:&h2 range:NSMakeRange(5,1)];

[datagetBytes:&h3 range:NSMakeRange(6,1)];

[datagetBytes:&h4 range:NSMakeRange(7,1)];

int h = (h1 << 24) + (h2 <<16) + (h3 << 8) + h4;

return CGSizeMake(w, h);

}

returnCGSizeZero;

}

+(CGSize)downloadGIFImageSizeWithRequest:(NSMutableURLRequest*)request

{

[request setValue:@"bytes=6-9"forHTTPHeaderField:@"Range"];

NSData* data = [NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror:nil];

if(data.length ==4)

{

short w1 = 0, w2 =0;

[datagetBytes:&w1 range:NSMakeRange(0,1)];

[datagetBytes:&w2 range:NSMakeRange(1,1)];

short w = w1 + (w2 << 8);

short h1 = 0, h2 =0;

[datagetBytes:&h1 range:NSMakeRange(2,1)];

[datagetBytes:&h2 range:NSMakeRange(3,1)];

short h = h1 + (h2 << 8);

return CGSizeMake(w, h);

}

returnCGSizeZero;

}

+(CGSize)downloadJPGImageSizeWithRequest:(NSMutableURLRequest*)request

{

[request setValue:@"bytes=0-209"forHTTPHeaderField:@"Range"];

NSData* data = [NSURLConnectionsendSynchronousRequest:request returningResponse:nilerror: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;

[datagetBytes:&w1 range:NSMakeRange(0x60,0x1)];

[datagetBytes:&w2 range:NSMakeRange(0x61,0x1)];

short w = (w1 << 8) + w2;

short h1 = 0, h2 =0;

[datagetBytes:&h1 range:NSMakeRange(0x5e,0x1)];

[datagetBytes:&h2 range:NSMakeRange(0x5f,0x1)];

short h = (h1 << 8) + h2;

return CGSizeMake(w, h);

}else {

short word = 0x0;

[datagetBytes:&word range:NSMakeRange(0x15,0x1)];

if (word == 0xdb) {

[datagetBytes:&word range:NSMakeRange(0x5a,0x1)];

if (word == 0xdb) {//两个DQT字段

short w1 = 0, w2 =0;

[datagetBytes:&w1 range:NSMakeRange(0xa5,0x1)];

[datagetBytes:&w2 range:NSMakeRange(0xa6,0x1)];

short w = (w1 << 8) + w2;

short h1 = 0, h2 =0;

[datagetBytes:&h1 range:NSMakeRange(0xa3,0x1)];

[datagetBytes:&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;

[datagetBytes:&w1 range:NSMakeRange(0x60,0x1)];

[datagetBytes:&w2 range:NSMakeRange(0x61,0x1)];

short w = (w1 << 8) + w2;

short h1 = 0, h2 =0;

[datagetBytes:&h1 range:NSMakeRange(0x5e,0x1)];

[datagetBytes:&h2 range:NSMakeRange(0x5f,0x1)];

short h = (h1 << 8) + h2;

return CGSizeMake(w, h);

}

}else {

return CGSizeZero;

}

@end

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