面试题

1. 什么是大端和小端？

• 大端模式：高位字节排放在内存的低地址端，低位字节排放在内存的高地址段。
• 小端模式：低位字节排放在内存的低地址端，高位字节排放在内存的高地址端。

2. 一个NSObject对象占用多少内存

• 系统分配了16个字节给NSObject对象（通过malloc_size函数获得）
• 但NSObject对象内部只使用了8个字节的空间（64bit环境下）

 NSObject *obj = [[NSObject alloc] init];
 NSLog(@"%zd", class_getInstanceSize([NSObject class]));
 NSLog(@"%zd", malloc_size((__bridge void *)obj));

3. ImageIO学习

- (void)viewDidLoad {
    [super viewDidLoad];

    
    UIImageView *iv = [[UIImageView alloc] initWithFrame:CGRectMake(60, 120, [UIScreen mainScreen].bounds.size.width - 120, 160)];
    [self.view addSubview:iv];
    
//
//    UIImage *image = [UIImage imageWithContentsOfFile:[[NSBundle mainBundle] pathForResource:@"11.jpeg" ofType:nil]];
//    NSData *data = UIImageJPEGRepresentation(image, 1.0);
//    SDImageFormat type = [NSData sd_imageFormatForImageData:data];
//    NSLog(@"%zd", type);
//
//    NSString *typeStr = (NSString *)[NSData sd_UTTypeFromImageFormat:type];
//    NSLog(@"%@", typeStr);
    
//    CGImageSourceRef source = CGImageSourceCreateWithData((__bridge CFDataRef)data, NULL);

    NSString *path = [[NSBundle mainBundle] pathForResource:@"show.gif" ofType:nil];
    NSURL *url = [NSURL fileURLWithPath:path];

    CGImageSourceRef source = CGImageSourceCreateWithURL((CFURLRef)url, NULL);

    long count = CGImageSourceGetCount(source);
    NSLog(@"图片个数%ld", count);
    //获取第几张图片
    CGImageRef firstImage = CGImageSourceCreateImageAtIndex(source, 23, NULL);

    NSArray *arr = CFBridgingRelease(CGImageSourceCopyTypeIdentifiers());
    NSLog(@"支持的类型\n%@", arr);

    NSString *type = CFBridgingRelease(CGImageSourceGetType(source));
    NSLog(@"所加载图片的类型为：%@", type);

    // 获取某一帧图片的缩略图
    CGImageRef thumbnailImage = CGImageSourceCreateThumbnailAtIndex(source, 0, NULL);
    NSLog(@"%@", thumbnailImage);
    
    CFDictionaryRef properties = CGImageSourceCopyPropertiesAtIndex(source, 0, NULL);
    
    NSInteger orientationValue = 1;
    CFTypeRef val = CFDictionaryGetValue(properties, kCGImagePropertyPixelHeight);
    // 图片的高度
    if (val) CFNumberGetValue(val, kCFNumberLongType, &_height);
    val = CFDictionaryGetValue(properties, kCGImagePropertyPixelWidth);
    // 图片的宽度
    if (val) CFNumberGetValue(val, kCFNumberLongType, &_width);
    val = CFDictionaryGetValue(properties, kCGImagePropertyOrientation);
    // 图片的方向
    if (val) CFNumberGetValue(val, kCFNumberNSIntegerType, &orientationValue);
    
    CFRelease(source);
    _orientation = (CGImagePropertyOrientation)orientationValue;
    
    
    iv.image = [UIImage imageWithCGImage:thumbnailImage];
}