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IOS 獲取網絡圖片大小實例詳解
在iOS開發過程中經常需要通過網絡請求加載圖片，有時，需要在創建UIImageView或UIButton來顯示圖片之前需要提前知道圖片的尺寸，根據圖片尺寸創建對應大小的控件。但是對于網絡圖片來說，要想通過最優的方法獲得尺寸就略微有點困難，大體思路就是下面這種：
如果有使用SDWebImage，則首先檢查是否緩存過該圖片，如果沒有，先通過文件頭獲取圖片大小(針對格式為png、gif、jpg文件獲取其尺寸大小)，如果獲取失敗，則下載完整的圖片data，然后計算大小，如果有使用SDWebImage，則使用SDWebImage緩存該圖片。
實例代碼：
+(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;
#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 cachePolicy:NSURLRequestUseProtocolCachePolicy timeoutInterval:1];
NSString* pathExtendsion = [URL.pathExtension lowercaseString];
CGSize size = CGSizeZero;
if ([pathExtendsion rangeOfString:@"png"].location != NSNotFound) {
size = [self downloadPNGImageSizeWithRequest:request];
}
else if([pathExtendsion rangeOfString:@"gif"].location != NSNotFound)
{
size = [self downloadGIFImageSizeWithRequest:request];
}
else{
size = [self downloadJPGImageSizeWithRequest:request];
}
if(CGSizeEqualToSize(CGSizeZero, size))
{
NSData* data = [NSData dataWithContentsOfURL:URL];
UIImage* image = [UIImage imageWithData:data];
if(image)
{
//如果未使用SDWebImage，則忽略；緩存該圖片
#ifdef dispatch_main_sync_safe
[[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:YES imageData:data forKey:URL.absoluteString toDisk:YES];
#endif
size = image.size;
}
}
//過濾掉不符合大小的圖片，大圖太大浪費流量，用戶體驗不好
if (size.height > 2048 || size.height <= 0 || size.width > 2048 || size.width <= 0 ) {
return CGSizeZero;
}
else
{
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 h2 = 0, h3 = 0, h4 = 0, h5 = 0;
[data getBytes:&h2 range:NSMakeRange(4, 1)];
[data getBytes:&h3 range:NSMakeRange(5, 1)];
[data getBytes:&h4 range:NSMakeRange(6, 1)];
[data getBytes:&h5 range:NSMakeRange(7, 1)];
int h = (h2 << 24) + (h3 << 16) + (h4 << 8) + h5;
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 h2 = 0, h3 = 0;
[data getBytes:&h2 range:NSMakeRange(2, 1)];
[data getBytes:&h3 range:NSMakeRange(3, 1)];
short h = h2 + (h3 << 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) {// 肯定只有一個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 h2 = 0, h3 = 0;
[data getBytes:&h2 range:NSMakeRange(0x5e, 0x1)];
[data getBytes:&h3 range:NSMakeRange(0x5f, 0x1)];
short h = (h2 << 8) + h3;
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) {// 兩個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 h2 = 0, h3 = 0;
[data getBytes:&h2 range:NSMakeRange(0xa3, 0x1)];
[data getBytes:&h3 range:NSMakeRange(0xa4, 0x1)];
short h = (h2 << 8) + h3;
return CGSizeMake(w, h);
} else {// 一個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 h2 = 0, h3 = 0;
[data getBytes:&h2 range:NSMakeRange(0x5e, 0x1)];
[data getBytes:&h3 range:NSMakeRange(0x5f, 0x1)];
short h = (h2 << 8) + h3;
return CGSizeMake(w, h);
}
} else {
return CGSizeZero;
}
}
}
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