判断图片格式

//枚举定义图片类型

{
    NSPUIImageType_JPEG,
    NSPUIImageType_PNG,
    NSPUIImageType_GIF,
    NSPUIImageType_Unknown
};

//定义方法

static inline NSPUIImageType NSPUIImageTypeFromData(NSData *imageData) {

    if (imageData.length > 4) {

        const unsigned char * bytes = [imageData bytes];

        

        if (bytes[0] == 0xff &&

            bytes[1] == 0xd8 &&

            bytes[2] == 0xff)

        {

            return NSPUIImageType_JPEG;

        }

        

        if (bytes[0] == 0x89 &&

            bytes[1] == 0x50 &&

            bytes[2] == 0x4e &&

            bytes[3] == 0x47)

        {

            return NSPUIImageType_PNG;

        }

        

        if (bytes[0] == 0x47)

        {

            return NSPUIImageType_GIF;

        }

    }

    

    return NSPUIImageType_Unknown;

}

//调用

    NSURL *url = [NSURL URLWithString:@"http://g.hiphotos.baidu.com/image/pic/item/c2cec3fdfc03924578c6cfe18394a4c27c1e25e8.jpg"];
    NSData *data = [NSData dataWithContentsOfURL:url];
    //NSData *data = [NSData dataWithContentsOfFile:@"/Users/apple/Desktop/book_cover.png"];

    NSPUIImageType type = NSPUIImageTypeFromData(data);
    if (type == NSPUIImageType_JPEG) {
        NSLog(@"JPEG");
    }else if (type == NSPUIImageType_PNG) {
        NSLog(@"PNG");
    }else if (type == NSPUIImageType_PNG) {
        NSLog(@"GIF");
    }else {
        NSLog(@"Unknown");
    }