根据url获取图片尺寸

```

// 根据图片url获取图片尺寸

-(CGSize)getImageSizeWithURL:(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;                  // url不正确返回CGSizeZero

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

NSString* pathExtendsion = [URL.pathExtension lowercaseString];

CGSize size = CGSizeZero;

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

size =  [self getPNGImageSizeWithRequest:request];

}

else{

size = [self getJPGImageSizeWithRequest:request];

}

if(CGSizeEqualToSize(CGSizeZero, size))                    // 如果获取文件头信息失败,发送异步请求请求原图

{

NSData* data = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:URL] returningResponse:nil error:nil];

UIImage* image = [UIImage imageWithData:data];

if(image)

{

size = image.size;

}

}

return size;

}

//  获取PNG图片的大小

-(CGSize)getPNGImageSizeWithRequest:(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;

}

//  获取jpg图片的大小

-(CGSize)getJPGImageSizeWithRequest:(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;

}

}

}

```