Swift 5 UIButton 標題沒變

Question

剛剛學習了Swift，開發了一個iOS的項目。

但是當我點擊它時按鈕標題不會改變。 如何更改標題？

模擬器：iPhone 11 iOS14.4

這是代碼：

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var helloButton: UIButton!
    
    @IBAction func showAlert(_ sender: Any) {
    //var alert = UIAlertController(title: "Hello!", message: "Hello, world!",preferredStyle: UIAlertControllerStyle.Alert)
    let alert = UIAlertController(title: "Hello", message: "Hello, world", preferredStyle: UIAlertController.Style.alert)
        
    alert.addAction(UIAlertAction(title: "close", style: UIAlertAction.Style.default, handler: nil))
        
    self.present(alert,animated:true,completion:nil)
    // ❌ it didn't work
    self.helloButton.setTitle("Clicked",for:.normal)     
    }
    
    override func viewDidLoad() {
      super.viewDidLoad()
    }
}

Answer 1

您尚未在代碼中調用 function showAlert()。 您需要在用戶單擊所需按鈕后立即調用 function，為此您需要使用 function，一旦發生單擊操作並調用和處理您所需的功能，就會調用它。

Answer 2

上面的代碼運行良好，並且標題發生了變化。 您還可以更新警報處理程序中的標題，如下所示。

   @IBAction func helloButtonTapped(_ sender: Any) {
    let alert = UIAlertController(title: "Hello", message: "Hello, world", preferredStyle: UIAlertController.Style.alert)
    alert.addAction(UIAlertAction(title: "close", style: .default, handler: { (_) in
        self.helloButton.setTitle("Clicked",for:.normal)
    }))
    self.present(alert,animated:true,completion:nil)}

Answer 3

我找到了原因！

這是因為 UIButton 標題是【Attributed】或【Plain】。

✅不同的屬性有不同的API改標題

如果是【Attributed】：我們應該把UIButton標題改成：

//
//  ViewController.swift
//  HelloCocoa
//
//  Created by LearnChild on 2021/4/14.
//

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var helloButton: UIButton!
    
    
    @IBAction func showAlert(_ sender: Any) {
//        var alert = UIAlertController(title: "Hello!", message: "Hello, world!",preferredStyle: UIAlertControllerStyle.Alert)
        let alert = UIAlertController(title: "Hello", message: "Hello, world", preferredStyle: UIAlertController.Style.alert)

        alert.addAction(UIAlertAction(title: "close", style: UIAlertAction.Style.default, handler: nil))

        self.present(alert,animated:true,completion:nil)

        //        if UIButton title is Plain
//        self.helloButton.setTitle("Clicked",for:.normal)
        
        
        
//        if UIButton title is Attributed✅👇
        let myNormalAttributedTitle = NSAttributedString(string: "Click Here",
                                                         attributes: [NSAttributedString.Key.foregroundColor : UIColor.blue])
        self.helloButton.setAttributedTitle(myNormalAttributedTitle,for:.normal)


    }

    
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }


}

如果是【普通】：

//
//  ViewController.swift
//  HelloCocoa
//
//  Created by LearnChild on 2021/4/14.
//

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var helloButton: UIButton!
    
    
    @IBAction func showAlert(_ sender: Any) {
//        var alert = UIAlertController(title: "Hello!", message: "Hello, world!",preferredStyle: UIAlertControllerStyle.Alert)
        let alert = UIAlertController(title: "Hello", message: "Hello, world", preferredStyle: UIAlertController.Style.alert)

        alert.addAction(UIAlertAction(title: "close", style: UIAlertAction.Style.default, handler: nil))

        self.present(alert,animated:true,completion:nil)

        //        if UIButton title is Plain✅👇
        self.helloButton.setTitle("Clicked",for:.normal)
        
        
        
//        if UIButton title is Attributed✅
//        let myNormalAttributedTitle = NSAttributedString(string: "Click Here",
//                                                         attributes: [NSAttributedString.Key.foregroundColor : UIColor.blue])
//        self.helloButton.setAttributedTitle(myNormalAttributedTitle,for:.normal)


    }

    

    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }


}