Swift/iOS : UIPicker display is not refreshed until tapped after changing the datasource programmatically

问题

In my app, I have a picker that's filled with data from my server after a POST request.

It has one element initially (used as a label), and when the POST request is filled the datasource get changed and I call picker.reloadAllComponents() to refresh it.

When this run, nothing appears to happen on screen, the picker doesn't change. But once tapped, the new data instantly appear and it works correctly. Seems like the data source change works correctly but the display doesn't change until refreshed.

Is there a way to refresh it, or a different method to change the datasource

Here's the relevant code :

class MyController: UIViewController, UIPickerViewDelegate, UIPickerViewDataSource {

@IBOutlet weak var dossiers_picker: UIPickerView!
var pickerData: [Dossier] = [Dossier(nom: "Dossier", id: 0)]
// Dossier is just a tuple class with 2 attributes

override func viewDidLoad() {
    super.viewDidLoad()
    self.dossiers_picker.delegate = self
    self.dossiers_picker.dataSource = self
    getDossiers()
}

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].nom
}

func getDossiers() {
    ... // Cut the code where I call the server to get the data, etc ...
    let task = session.dataTask(with: request) { data, response, error in
        guard let data = data, error == nil else {
                // check for fundamental networking error
                print("error=\(String(describing: error))")
                return
            }
        ... // get the data and turn it into an array of Dossier classes in var dossiers
        self.pickerData = dossiers
        dossiers_picker.reloadAllComponents()
    }
    task.resume()
}
}

回答1:

Figured it out when adding the asynchronous tag to the question... good old rubber duck debugging.

As said by @rmaddy, all UI updates must be done on the main thread.

In this case, replace

dossiers_picker.reloadAllComponents()

with

DispatchQueue.main.async {
    self.dossiers_picker.reloadAllComponents()
}

来源：https://stackoverflow.com/questions/45221065/swift-ios-uipicker-display-is-not-refreshed-until-tapped-after-changing-the-da

标签

ios

swift

user-interface

asynchronous

picker