如何移动uibutton来为小型门腾出空间？

Question

我有一个snackbar，有时会出现在我的视图控制器上。但是当出现时，它会阻止已经存在的Uibutton。如何移动按钮以适应Snackbar，而无需硬编码移动按钮的位置？

谢谢！

Answer 1

您可以通过将按钮的底部约束取决于Snackbar容器的顶部约束来做到这一点（如果Snackbar从上方降下）。当什么都没发生时，Snackbar容器高度为零，并且在显示Snackbar时会展开。

但是，我会提出另一种方法。 Snackbars通常不会取代UI，我想用户“错过”按钮会感到沮丧，因为该应用显示Snackbar。另请参见材料设计指南这些事情如何工作。 （它们不是iOS的本地，因此据我所知，苹果没有任何文件）。

Answer 2

这可以通过为按钮的底部约束声明两个不同的nslayoutconstraints，一个基于安全区域（或最初相对于您的按钮定位），而另一个基于Snackbar的位置。然后，通过设置约束属性的属性 false 和true之间，实际使用哪个约束。

我已经在此处确认这有效：

import UIKit

class ViewController: UIViewController {
    // Connect an outlet to the button to allow adding the new constraint
    // to it programatically
    @IBOutlet weak var movingButton: UIButton!
    
    // This is the bottom constraint of the UIButton which will change based on whether or not
    // the snackbar is open.  It was set up in Main.storyboard with parameters as follows:
    // -- First Item:   Button.Bottom
    // -- Relation:     Equal
    // -- Second Item:  Safe Area.Bottom
    // -- Constant:     0
    // -- Priority:     1000
    // -- Multiplier:   1
    @IBOutlet var buttonBottomConstraint: NSLayoutConstraint!
    // Note:  do not use 'weak var' for this constraint, as this would cause a nil exception as the
    // constraint would get deleted as soon as its .isActive property is set to false inside toggleSnackbar
    
    // Will be determined by the snackbar at its initialization
    var newButtonBottomConstraint: NSLayoutConstraint?
    
    // Will be set inside viewDidLayoutSubviews
    var screenWidth: Double?
    var screenHeight: Double?
    
    var snackbar: UILabel?
    var snackbarIsOpen = false
    
    override func viewDidLoad() {
        super.viewDidLoad()
    }
    
    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()
        if screenWidth == nil {
            // These will depend on the device (iPhone, iPad etc.)
            screenWidth = view.safeAreaLayoutGuide.layoutFrame.width;
            screenHeight = view.safeAreaLayoutGuide.layoutFrame.height;
        }
        // Only instantiate snackbar once, not every time
        // viewDidLayoutSubviews is called.
        if snackbar == nil {
            snackbar = UILabel(frame: CGRect(x: 0.1*screenWidth!, y: 0.95*screenHeight!, width: 0.8*screenWidth!, height: 0.1*screenHeight!))
            snackbar?.backgroundColor = .systemGray
            snackbar?.textColor = .white
            snackbar?.numberOfLines = 2
            snackbar?.textAlignment = .center
            snackbar?.font = UIFont.systemFont(ofSize: 18)
            snackbar?.text = "When this appears, the button will move upwards."
            
            // This constraint will replace movingButton's IBOutlet constraint when the snackbar is open
            newButtonBottomConstraint = NSLayoutConstraint(item: movingButton!, attribute: .bottom, relatedBy: .equal, toItem: snackbar!, attribute: .top, multiplier: 1, constant: -10)
        }
    }

    @IBAction func toggleSnackbar(_ sender: UIButton) {
        // Close the snackbar if it's already open
        if snackbarIsOpen {
            snackbar?.removeFromSuperview()
            sender.setTitle("Press For Snackbar", for: .normal)
            snackbarIsOpen = false
            
            movingButton.setTitle("Will Move", for: .normal)
            // Swap which constraint is active:  back to original storyboard value
            newButtonBottomConstraint?.isActive = false
            buttonBottomConstraint.isActive = true
        } else {
            // Open the snackbar if it isn't already open
            view.addSubview(snackbar!)
            sender.setTitle("Dismiss Snackbar", for: .normal)
            snackbarIsOpen = true
            
            movingButton.setTitle("Did Move", for: .normal)
            // Swap which constraint is active:  use new constraint based on snackbar's position
            buttonBottomConstraint.isActive = false
            newButtonBottomConstraint?.isActive = true
        }
    }
}

附加详细信息：按钮设置在Main.Storyboard中，除了相对于Snackbar的限制外，所有约束也是如此。我在代码示例的注释中包括了与示例相关的接口构建器值（按钮的底部约束）。