我试图实现模态呈现效果，其中呈现的视图仅部分覆盖父视图，如下图所示。

我知道我可以通过使用实现自定义转换来实现这一点UIPresentationController。我不想重新发明轮子，所以在继续开发之前我想问一下。

API 中是否有对这种转换的内置支持？

我研究了所有可用的模态呈现样式 https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIViewController_Class/index.html#//apple_ref/c/tdef/UIModalPresentationStyle在我看来，我想要进行的转换没有得到支持，实现它的唯一方法就是对其进行编码。

我遇到了完全相同的问题。我也沿着模态演示风格路线前进，但一直碰壁（特别是让它在 iPhone 而不是 iPad 上工作）。

经过一番挖掘后，我终于能够让它工作了。我是这样做的：

首先，我们需要一个将要呈现的视图控制器（模态控制器），将其视图的背景颜色设置为透明，并将导航控制器视图的框架设置为某个偏移量。

模态视图控制器.h

@import UIKit;

@class ModalViewController;

@protocol ModalViewControllerDelegate <NSObject>

- (void)modalViewControllerDidCancel:(ModalViewController *)modalViewController;

@end

@interface ModalViewController : UIViewController
@property (weak, nonatomic) id<ModalViewControllerDelegate> delegate;

- (instancetype)initWithRootViewController:(UIViewController *)rootViewController;
@end

ModalViewController.m

static const CGFloat kTopOffset = 50.0f;

@implementation ModalViewController {
    UINavigationController *_navController;
}

- (instancetype)initWithRootViewController:(UIViewController *)rootViewController
{
    self = [super initWithNibName:nil bundle:nil];
    if (self) {
        rootViewController.navigationItem.leftBarButtonItem = [self cancelButton];
        _navController = [[UINavigationController alloc] initWithRootViewController:rootViewController];
        self.view.backgroundColor = [UIColor clearColor];
        [self.view addSubview:_navController.view];

        // this is important (prevents black overlay)
        self.modalPresentationStyle = UIModalPresentationOverFullScreen;
    }

    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    CGRect bounds = self.view.bounds;
    _navController.view.frame = CGRectMake(0, kTopOffset, CGRectGetWidth(bounds), CGRectGetHeight(bounds) - kTopOffset);
}

- (UIBarButtonItem *)cancelButton
{
    return [[UIBarButtonItem alloc] initWithTitle:@"Cancel" style:UIBarButtonItemStylePlain target:self action:@selector(cancelButtonClicked:)];
}

- (void)cancelButtonClicked:(id)sender
{
    [_delegate modalViewControllerDidCancel:self];
}

@end

接下来，我们需要设置呈现控制器来运行以下动画：

• 缩小自身规模
• 淡出一点点
• 使用以下方式呈现模态视图控制器presentViewController:animated:completion

这就是我所做的

呈现ViewController.m

static const CGFloat kTransitionScale = 0.9f;
static const CGFloat kTransitionAlpha = 0.6f;
static const NSTimeInterval kTransitionDuration = 0.5;

@interface PresentingViewController <ModalViewControllerDelegate>
@end

@implementation PresentingViewController
...
...

- (void)showModalViewController
{
    self.navigationController.view.layer.shouldRasterize = YES;
    self.navigationController.view.layer.rasterizationScale = [UIScreen mainScreen].scale;

    UIViewController *controller = // init some view controller
    ModalViewController *container = [[ModalViewController alloc] initWithRootViewController:controller];
    container.delegate = self;

    __weak UIViewController *weakSelf = self;
    [UIView animateWithDuration:kTransitionDuration animations:^{
        weakSelf.navigationController.view.transform = CGAffineTransformMakeScale(kTransitionScale, kTransitionScale);
        weakSelf.navigationController.view.alpha = kTransitionAlpha;
        [weakSelf presentViewController:container animated:YES completion:nil];
    } completion:^(BOOL finished) {
        weakSelf.navigationController.view.layer.shouldRasterize = NO;
    }];
}

#pragma mark - ModalViewControllerDelegate

- (void)modalViewControllerDidCancel:(ModalViewController *)modalViewController
{
    __weak UIViewController *weakSelf = self;
    [UIView animateWithDuration:kTransitionDuration animations:^{
        weakSelf.navigationController.view.alpha = 1;
        weakSelf.navigationController.view.transform = CGAffineTransformIdentity;
        [weakSelf dismissViewControllerAnimated:YES completion:nil];
    }];
}
@end