我为 UIAlertController（在 Swift 4 中）编写了一个扩展，它解决了自动布局的布局问题。甚至还有一个备用消息字符串以防万一（由于 UIAlertController 布局的未来更改）。
import Foundation
extension UIAlertController {
/// Creates a `UIAlertController` with a custom `UIView` instead the message text.
/// - Note: In case anything goes wrong during replacing the message string with the custom view, a fallback message will
/// be used as normal message string.
///
/// - Parameters:
/// - title: The title text of the alert controller
/// - customView: A `UIView` which will be displayed in place of the message string.
/// - fallbackMessage: An optional fallback message string, which will be displayed in case something went wrong with inserting the custom view.
/// - preferredStyle: The preferred style of the `UIAlertController`.
convenience init(title: String?, customView: UIView, fallbackMessage: String?, preferredStyle: UIAlertController.Style) {
let marker = "__CUSTOM_CONTENT_MARKER__"
self.init(title: title, message: marker, preferredStyle: preferredStyle)
// Try to find the message label in the alert controller's view hierarchie
if let customContentPlaceholder = self.view.findLabel(withText: marker),
let customContainer = customContentPlaceholder.superview {
// The message label was found. Add the custom view over it and fix the autolayout...
customContainer.addSubview(customView)
customView.translatesAutoresizingMaskIntoConstraints = false
customContainer.addConstraints(NSLayoutConstraint.constraints(withVisualFormat: "H:|-[customView]-|", options: [], metrics: nil, views: ["customView": customView]))
customContainer.addConstraint(NSLayoutConstraint(item: customContentPlaceholder,
attribute: .top,
relatedBy: .equal,
toItem: customView,
attribute: .top,
multiplier: 1,
constant: 0))
customContainer.addConstraint(NSLayoutConstraint(item: customContentPlaceholder,
attribute: .height,
relatedBy: .equal,
toItem: customView,
attribute: .height,
multiplier: 1,
constant: 0))
customContentPlaceholder.text = ""
} else { // In case something fishy is going on, fall back to the standard behaviour and display a fallback message string
self.message = fallbackMessage
}
}
}
private extension UIView {
/// Searches a `UILabel` with the given text in the view's subviews hierarchy.
///
/// - Parameter text: The label text to search
/// - Returns: A `UILabel` in the view's subview hierarchy, containing the searched text or `nil` if no `UILabel` was found.
func findLabel(withText text: String) -> UILabel? {
if let label = self as? UILabel, label.text == text {
return label
}
for subview in self.subviews {
if let found = subview.findLabel(withText: text) {
return found
}
}
return nil
}
}
这是一个使用示例：
// Create a custom view for testing...
let customView = UIView()
customView.translatesAutoresizingMaskIntoConstraints = false
customView.backgroundColor = .red
// Set the custom view to a fixed height. In a real world application, you could use autolayouted content for height constraints
customView.addConstraint(NSLayoutConstraint(item: customView,
attribute: .height,
relatedBy: .equal,
toItem: nil,
attribute: .notAnAttribute,
multiplier: 1,
constant: 100))
// Create the alert and show it
let alert = UIAlertController(title: "Alert Title",
customView: customView,
fallbackMessage: "This should be a red rectangle",
preferredStyle: .actionSheet)
alert.addAction(UIAlertAction(title: "Yay!", style: .default, handler: nil))
alert.addAction(UIAlertAction(title: "Cancel", style: .cancel, handler: nil))
self.present(alert, animated: true, completion: nil)
这将显示如下内容：