Custom control picker bindable selected item don't work at the initialisation-CodePudding

I got an issue when trying to create a custom control with a picker inside. I create a bindable property

public static readonly BindableProperty PhoneCodeProperty = BindableProperty.Create(nameof(PhoneCode),
            typeof(PhoneIndex),
            typeof(PhoneEntry),
            defaultBindingMode: BindingMode.TwoWay,
            propertyChanged: PhoneCodePropertyChanged);

private static void PhoneCodePropertyChanged(BindableObject bindable, object oldValue, object newValue)
{
      PhoneEntry control = (PhoneEntry)bindable;

      control.Picker.SelectedItem = newValue ?? oldValue;
      Console.WriteLine($"Picker Value => {control.Picker.SelectedItem}");

}

public PhoneIndex PhoneCode
{
      get => (PhoneIndex)GetValue(PhoneCodeProperty);

      set => SetValue(PhoneCodeProperty, value);
}

Then I populate my picker and set the value that I want to show first in the constructor of my control :

phoneNumberUtil = PhoneNumberUtil.GetInstance();
var callingcode = phoneNumberUtil.GetSupportedRegions();


PhoneCodesStrings = new List<PhoneIndex>();

foreach (string CountryCode in callingcode)
{
      PhoneCodesStrings.Add(new PhoneIndex(CountryCode, phoneNumberUtil.GetCountryCodeForRegion(CountryCode)));
}

PhoneCodesStrings.Sort(CompareByCountryCode);
Picker.ItemsSource = PhoneCodesStrings;
Predicate<PhoneIndex> predicate = IsFr;

Picker.SelectedIndexChanged  = Picker_SelectedIndexChanged;
Entry.TextChanged  = Entry_TextChanged;

PhoneCode = PhoneCodesStrings.Find(predicate);

And after this I call my control like that :

<controls:PhoneEntry
                    Margin="0,8,0,0"
                    PhoneCode="{Binding CurrentIndex}"
                    PhoneNumber="{Binding CurrentPhoneNumber}"
                    ValidPhoneNumber="{Binding ValidPhoneNumber}" />

My picker is set OK, I can see it with any problem in my UI, but I don't get any value in my viewmodel until the user change the value of the picker

Does anyone know why ? Thanks in advance !

CodePudding user response：

I think my problem is solved and it was the binding mode that cause my issue. I set it to onewaytosource and then it was ok

CodePudding user response：

you want to set a default value for a bindableproperty. you must set it to defaultValueCreator parameter.

public static readonly BindableProperty PhoneCodeProperty = BindableProperty.Create(nameof(PhoneCode),
            typeof(PhoneIndex),
            typeof(PhoneEntry),
            defaultBindingMode: BindingMode.TwoWay,
            propertyChanged: PhoneCodePropertyChanged
            defaultValueCreator: PhoneCodeDefaultValue);

public static PhoneIndex PhoneCodeDefaultValue(BindableObject bindable)
{
           PhoneCodesStrings = new List<PhoneIndex>();

           foreach (string CountryCode in callingcode)
           {
                PhoneCodesStrings.Add(new PhoneIndex(CountryCode,phoneNumberUtil.GetCountryCodeForRegion(CountryCode)));
           }
           Predicate<PhoneIndex> predicate = IsFr;
           return PhoneCodesStrings.Find(predicate);
 }