Swift 3 UIPicker

Question

为了更好地学习Swift 3/ iOS，我做了一个小小的测试应用程序。我刚开始使用Swift 2，但是停止了，所以回到它，但是有这么多的iOS需要学习！

它似乎工作得很好，所以当用户按下“完成”按钮时，我将选择视图值插入到textfield中。我发现如果没有这样做，如果用户想要选择视图的第一个值，就不会像滚动到另一个值时那样插入。我留下了控制器的相关代码。

class ViewController: UITableViewController, UIPickerViewDataSource, UIPickerViewDelegate {
 let pickerData: [String] = ["1", "2", "3", "4"]
 var picker = UIPickerView()

 @IBOutlet weak var textField: UITextField!

 // set the pickerview for number of periods
func setPickerView(){
    picker.dataSource = self
    picker.delegate = self
    textField.inputView = picker
    textField.inputAccessoryView = initToolBar()
}

// build the toolbar for uipicker, so a user can select a value
func initToolBar() -> UIToolbar {
    let toolBar = UIToolbar()
    toolBar.barStyle = UIBarStyle.default
    toolBar.isTranslucent = true
    toolBar.tintColor = UIColor(red:14.0/255, green:122.0/255, blue:254.0/255, alpha: 1)
    toolBar.sizeToFit()
    // TODO need to update actions for all buttons
    let cancelButton = UIBarButtonItem(title: "Cancel", style: UIBarButtonItemStyle.plain, target: self, action: nil)
    let doneButton = UIBarButtonItem(title: "Done", style: UIBarButtonItemStyle.plain, target: self, action: #selector(pickerDoneAction))
    let spaceButton = UIBarButtonItem(barButtonSystemItem: UIBarButtonSystemItem.flexibleSpace, target: nil, action: nil)
    toolBar.setItems([cancelButton, spaceButton, doneButton], animated: false)
    toolBar.isUserInteractionEnabled = true

    return toolBar
}

// Take pickerview value and insert into textfield, this stops the first row on load not being loaded into textfield
func pickerDoneAction(sender: UITextField){
    let indexPath = picker.selectedRow(inComponent: 0)
    textField.text = pickerData[indexPath]
    // resign first responder dropping the uipicker
    UIApplication.shared.sendAction(#selector(resignFirstResponder), to:nil, from:nil, for:nil)
}

// Pickerview delegates
func numberOfComponents(in pickerView: UIPickerView) -> Int { return 1 }
func pickerView(_ pickerView: UIPickerView, numberOfRowsInComponent component: Int) -> Int {return pickerData.count}
func pickerView(_ pickerView: UIPickerView, titleForRow row: Int, forComponent component: Int) -> String? {return pickerData[row]}
func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
    textField.text = pickerData[row]
}
 }

如果代码非常合适，并让它在同一个屏幕上具有不同数据源的多个uipickers上工作，我想使用这个方法。虽然我还不太确定

Answer 1

一个简单的修复方法是在数据源的开头添加一个空的额外值。

设pickerData：字符串 = “、”1“、”2“、”3“、”4“

或者，只要他们开始编辑let textField.text = pickerData[0]，您就可以立即使用textField。