UIButton以编程方式创建但未显示在视图上(addSubview被调用)

let button = UIButton(type: .system)
button.frame = CGRect(x: 100, y: 100, width: 100, height: 50)
button.setTitle("Click Me", for: .normal)
button.addTarget(self, action: #selector(buttonClicked), for: .touchUpInside)
view.addSubview(button)

button.translatesAutoresizingMaskIntoConstraints = false
NSLayoutConstraint.activate([
    button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
    button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
    button.widthAnchor.constraint(equalToConstant: 100),
    button.heightAnchor.constraint(equalToConstant: 50)
])

@objc func buttonClicked(sender: UIButton) {
    // 处理按钮点击事件
}