Ios 使用视觉格式语言计算不需要的按钮高度

我有一个

UIViewController

，上面有四个

uibutton

（2 x 2），我在interface builder中展示了它，它工作得非常好。我将有一个免费的、支持广告的应用程序版本，所以我需要根据应用程序是付费版本还是支持广告的版本重做该场景以加载。基于此，我尝试使用可视化格式语言来布局视图。我得到的

ui按钮高度值不正确，尽管我在计算高度时考虑了高度。我想不出我的错误（或遗漏？）

这是我的界面生成器的屏幕截图。

我在interface builder中的按钮没有限制，但我有连接到
MyViewController
的
IBOutlets
MyViewController
位于导航控制器中，底部有一个选项卡栏

我创建了一个名为
layoutButtons
的方法，在
super.viewDidLoad（）
之后调用该方法。这是：

func layoutButtons() {
    // Configure layout constraints

    // Remove interface builder constraints from storyboard
    view.removeConstraints(view.constraints)

    // create array to dump constraints into
    var allConstraints = [NSLayoutConstraint]()

    // determine screen size
    let screenSize: CGRect = UIScreen.mainScreen().bounds

    let navBarRect = navigationController!.navigationBar.frame
    let navBarHeight = navBarRect.height

    let tabBarRect = tabBarController!.tabBar.frame
    let tabBarHeight: CGFloat = tabBarRect.height

    // calculate button width based on screen size

    // padding for left + middle + right = 8.0 + 8.0 + 8.0 = 24.0
    let buttonWidth = (screenSize.width - 24.0) / 2

    /*
    My buttons are extending under the top & bottom layout guides despite accounting
    for them when I set the buttonHeight.
    */

    // padding for top + middle + bottom = 8.0 + 8.0 + 8.0 = 24.0
    let buttonHeight = (screenSize.height - topLayoutGuide.length - bottomLayoutGuide.length - 24.0) / 2

    // create dictionary of metrics
    let metrics = ["buttonWidth": buttonWidth,
        "buttonHeight": buttonHeight,
        "navBarHeight": navBarHeight,
        "tabBarHeight": tabBarHeight,
        "bannerAdWidth": bannerAdWidth,
        "bannerAdHeight": bannerAdHeight]

    // create dictionary of views
    var views: [String : AnyObject] = ["firstButton": firstButton,
        "secondButton": secondButton,
        "thirdButton": thirdButton,
        "fourthButton": fourthButton,
        "topLayoutGuide": topLayoutGuide,
        "bottomLayoutGuide": bottomLayoutGuide]

    let topRowHorizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "H:|-[firstButton(buttonWidth)]-[secondButton(buttonWidth)]-|",
        options: [.AlignAllCenterY],
        metrics: metrics,
        views: views)
    allConstraints += topRowHorizontalConstraints

    let bottomRowHorizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "H:|-[thirdButton(buttonWidth)]-[fourthButton(buttonWidth)]-|",
        options: [.AlignAllCenterY],
        metrics: metrics,
        views: views)
    allConstraints += bottomRowHorizontalConstraints

    let leftColumnVerticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:|[topLayoutGuide]-[firstButton(buttonHeight)]-[thirdButton(buttonHeight)]-[bottomLayoutGuide]|",
        options: [],
        metrics: metrics,
        views: views)
    allConstraints += leftColumnVerticalConstraints

    let rightColumnVerticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:|[topLayoutGuide]-[secondButton(buttonHeight)]-[fourthButton(buttonHeight)]-[bottomLayoutGuide]|",
        options: [],
        metrics: metrics,
        views: views)
    allConstraints += rightColumnVerticalConstraints

    NSLayoutConstraint.activateConstraints(allConstraints)
}

我摆弄了我的
buttonHeight
变量，但我尝试的每次迭代都会导致按钮在
topLayoutGuide
和
bottomLayoutGuide
下扩展。下面是它在运行时的样子：


我欢迎任何关于在哪里寻找我的错误的建议。谢谢阅读。
我最初遵循的是a，教程的设置与我的类似，即
子视图
位于故事板上，并通过
IBOutlets
连接到
MyViewController

出于绝望，我在脚本中创建了
ui按钮。一路上，我发现我的问题是，我设置按钮上的图像之前，它的布局这个故事的寓意是，在按钮布置好之前，不要在按钮上设置图像

下面是从my
viewDidLoad
中的一个方法调用的代码，该方法布置了一个2 x 2的按钮网格：

    // Configure Buttons
    firstButton.translatesAutoresizingMaskIntoConstraints = false
    // code to customize button

    secondButton.translatesAutoresizingMaskIntoConstraints = false
    // code to customize button

    thirdButton.translatesAutoresizingMaskIntoConstraints = false
    // code to customize button

    fourthButton.translatesAutoresizingMaskIntoConstraints = false
    // code to customize button

    // Add buttons to the subview
    view.addSubview(firstButton)
    view.addSubview(secondButton)
    view.addSubview(thirdButton)
    view.addSubview(fourthButton)

    // create views dictionary
    var allConstraints = [NSLayoutConstraint]()

    let views: [String : AnyObject] = ["firstButton": firstButton,
        "secondButton": secondButton,
        "thirdButton": thirdButton,
        "fourthButton": fourthButton,
        "topLayoutGuide": topLayoutGuide,
        "bottomLayoutGuide": bottomLayoutGuide]

    // Calculate width and height of buttons
    // 24.0 = left padding + middle padding + right padding
    let buttonWidth = (screenSize.width - 24.0) / 2
    let buttonHeight = (screenSize.height - topLayoutGuide.length - bottomLayoutGuide.length - 24.0) / 2

    // Create a dictionary of metrics
    let metrics = ["buttonWidth": buttonWidth,
    "buttonHeight" : buttonHeight]

    let topVerticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:|[topLayoutGuide]-[firstButton(buttonHeight)]",
        options: [],
        metrics: metrics,
        views: views)
    allConstraints += topVerticalConstraints

    let topRowHorizontalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "H:|-[firstButton(buttonWidth)]-[secondButton(==firstButton)]-|",
        options: NSLayoutFormatOptions.AlignAllCenterY,
        metrics: metrics,
        views: views)
    allConstraints += topRowHorizontalConstraints

    let bottomRowHorizontalContraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "H:|-[thirdButton(buttonWidth)]-[fourthButton(==thirdButton)]-|",
        options: NSLayoutFormatOptions.AlignAllCenterY,
        metrics: metrics,
        views: views)
    allConstraints += bottomRowHorizontalContraints

    let leftColumnVerticalConstraints = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:[firstButton]-[thirdButton(==firstButton)]-[bottomLayoutGuide]-|",
        options: [],
        metrics: metrics,
        views: views)
    allConstraints += leftColumnVerticalConstraints

    let rightColumnVerticalConstriants = NSLayoutConstraint.constraintsWithVisualFormat(
        "V:[secondButton(buttonHeight)]-[fourthButton(==secondButton)]-[bottomLayoutGuide]-|",
        options: [],
        metrics: metrics,
        views: views)
    allConstraints += rightColumnVerticalConstriants

    NSLayoutConstraint.activateConstraints(allConstraints)

    // ** DON'T SET IMAGES ON THE BUTTONS UNTIL THE BUTTONS ARE LAID OUT!!!**
    firstButton.imageView?.contentMode = UIViewContentMode.ScaleAspectFit
    firstButton.setImage(UIImage(named: "first.png"), forState: .Normal)

    secondButton.imageView?.contentMode = UIViewContentMode.ScaleAspectFit
    secondButton.setImage(UIImage(named: "second.png"), forState: .Normal)

    thirdButton.imageView?.contentMode = UIViewContentMode.ScaleAspectFit
    thirdButton.setImage(UIImage(named: "third.png"), forState: .Normal)

    fourthButton.imageView?.contentMode = UIViewContentMode.ScaleAspectFit
    fourthButton.setImage(UIImage(named: "fourth.png"), forState: .Normal)

从
视图将出现
或
视图显示
运行您的方法。在
viewDidLoad
中，尚未计算视图的实际大小。因为您的高度计算取决于视图高度，所以需要在正确的位置调用它。另外，您实际希望它看起来像什么？我希望在导航栏和选项卡栏之间绘制所有4个按钮。为什么要对按钮使用高度和宽度约束？让他们有相同的层次和宽度不是很好吗？@Fogmeister谢谢你。我在
viewwillbeen
和
viewdidebeen
中尝试过，但运气不佳。