iOS底部将对象与程序化自动布局约束对齐

Question

我试图放置一个按钮，使其始终是屏幕底部的X像素。 使用自动布局以编程方式对视图进行布局。 如果使用： @"V:|-44-[closeModalButton]" ，对象将按预期从屏幕顶部对齐44个像素。 但是， @"V:[closeModalButton]-44-|" 导致按钮永不显示。 似乎应该很简单，所以我觉得我缺少真正明显的东西。

执行视图

#import "DetailView.h"

@implementation DetailView

@synthesize closeModalButton;

- (id)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        // Initialization code
        self.backgroundColor = [UIColor whiteColor];
        CGRect aFrame = [[UIScreen mainScreen] bounds];
        self.frame = aFrame;

        closeModalButton = [UIButton buttonWithType:UIButtonTypeCustom];
        [closeModalButton setImage: [UIImage imageNamed:@"closeButton.png"] forState:UIControlStateNormal];
        [closeModalButton setTranslatesAutoresizingMaskIntoConstraints:NO];
        [self addSubview:closeModalButton];

        NSDictionary *viewArranging = NSDictionaryOfVariableBindings(closeModalButton);

        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[closeModalButton(44)]-44-|"
                                                                     options:0
                                                                     metrics:0
                                                                       views:viewArranging]];

        [self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-149-[closeModalButton(44)]-149-|"
                                                                     options:0
                                                                     metrics:0
                                                                       views:viewArranging]];
    }
    return self;
}

@end

视图控制器

#import "DetailViewController.h"

@interface DetailViewController ()

@end

@implementation DetailViewController
{
    DetailView *_detailView;
}

- (void)loadView
{    
    _detailView = [[DetailView alloc] init];
    [self setView:_detailView];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.

    [_detailView.closeModalButton addTarget:self
                                     action:@selector(closeModalButtonPressed:)
                           forControlEvents:UIControlEventTouchUpInside];

}

- (void)closeModalButtonPressed:(UIButton *)sender{
    [self dismissViewControllerAnimated:YES
                             completion:nil];
}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

@end

Answer 1

好的，因此看起来DetailView.h继承了UIScrollView而不是UIView。 设置适当的子类会导致约束按预期运行。