Swift开发：UIPickerView显示异常、崩溃及日期同步问题

Hey there, fellow Swift newbie! Let's break down each of your UIPickerView issues one by one and fix them step by step:

1. UIPickerView displays on view controller load instead of being hidden #

This is a common gotcha when setting up pickers for the first time. Here's how to fix it:

• If you're using Storyboards/XIBs: Select your UIPickerView in the interface builder, head to the Attributes Inspector, and check the Hidden checkbox to set its initial state.
• If you're creating it programmatically: Add yourPickerView.isHidden = true inside your viewDidLoad() method. This ensures it stays hidden until you explicitly show it (like when the user taps the birth date text field).

2. App crashes when tapping the Done button on the UIPickerView #

Crashes here almost always tie to issues with the button's target-action setup, especially since UIKit relies on Objective-C runtime compatibility for these callbacks. Here's what to check:

• Make sure your Done button's handler method is marked with @objc. For example:

  @objc func doneButtonTapped() {
      yourPickerView.isHidden = true
      // Don't forget to update the text field with the selected date here!
  }
  

• Double-check the addTarget call if you're creating the button programmatically—ensure the selector matches your method name exactly:

  doneButton.addTarget(self, action: #selector(doneButtonTapped), for: .touchUpInside)
  

• Confirm the toolbar holding the Done button is properly added to your view hierarchy, and that neither the button nor picker has a nil reference.

3. UIPickerView doesn't sync selected date to UITextField #

You need to leverage the UIPickerView delegate method that triggers when a row is selected, then update your text field directly from there. Here's how:

1. First, verify your view controller conforms to UIPickerViewDelegate and UIPickerViewDataSource (you likely have this set up already, but it's worth a double-check).
2. Implement the pickerView(_:didSelectRow:inComponent:) method to capture selected date components and format them into a string for your text field:

   func pickerView(_ pickerView: UIPickerView, didSelectRow row: Int, inComponent component: Int) {
       // Replace these arrays with your actual year/month/day data sources
       let selectedYear = yearOptions[pickerView.selectedRow(inComponent: 0)]
       let selectedMonth = monthOptions[pickerView.selectedRow(inComponent: 1)]
       let selectedDay = dayOptions[pickerView.selectedRow(inComponent: 2)]
       
       birthDateTextField.text = "\(selectedYear)-\(selectedMonth)-\(selectedDay)"
   }
   

3. If you want a default date to show when the screen loads, you can either set birthDateTextField.text directly in viewDidLoad() or manually call the delegate method to populate it.

Bonus tip: Instead of manually managing picker visibility, set it as the inputView of your birth date text field. Tapping the text field will automatically bring up the picker, and you can add a toolbar with the Done button to the inputAccessoryView for dismissal—it's a more native iOS pattern!

内容的提问来源于stack exchange，提问作者user9432913