[IOS][Swift]点击TextField弹出UIPickerView-选择框(swift)

1.创建一个PickerView

1.1 Storyboard

1. 选择Pick View 拖进Storyboard
2. 按住ctrl，把刚加入的“Pick View”拖到对应的ViewController类中
   @IBOutlet weak var classifyPickerView: UIPickerView!

1.2 对应的ViewController类修改

1.2.1 继承相关类和初始化

1. viewcontroller需要继承UIPickerViewDelegate, UIPickerViewDataSource
   继承后有两个必须要实现的函数

    
    //返回选择框的列数
    func numberOfComponents(in pickerView: UIPickerView) -> Int {
        return 1
    }
    //返回选择框的行数
    func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {
        return pickViewDataSource.count
    }

2. 在override func viewDidLoad()的时候对PickerView的数据来源和delegate初始化

       //pickView
        classifyPickerView.dataSource = self
        classifyPickerView.delegate = self
        //设置默认显示值
        classifyPickerView.showsSelectionIndicator = true
        

1.2.2 添加需要显示的数据

1.定义PickerView需要显示的数据

    //MARK: Private Data
    private let pickViewDataSource = ["a", "b", "c"]

2.重写函数titleForRow来显示数据

    func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {
        return pickViewDataSource[row]
    }

2. 定义一个文本框(Text Field)，用户点击文本框弹出pickerView

2.1 Storyboard

1. 选择Text Field, 拖进Storyboard
2. 按住ctrl，把刚加入的“Text Field”拖到对应的ViewController类中

@IBOutlet weak var classifyTextField: UITextField!

2.2 对应的ViewController类修改

2.2.1 继承相关类和初始化

1. viewcontroller需要继承UITextFieldDelegate
2. 在override func viewDidLoad()的时候对TextField的delegate初始化

classifyTextField.delegate = self

2.2.2 点击TextField，弹出PickerView

TextField的默认动作是弹出键盘，需要重写函数textFieldShouldBeginEditing修改默认行为

    func textFieldShouldBeginEditing(_ textField: UITextField) -> Bool {
        if textField == self.classifyTextField {
            self.classifyTextField.inputView = self.classifyPickerView
            classifyPickerView.isHidden = false
            classifyPickerView.removeFromSuperview()
        }
        
        return true
    }

2.2.3 用户选中的PickerView数据显示到TextField

    func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
        classifyTextField.text = pickViewDataSource[row]
        classifyPickerView.layoutIfNeeded()
    }