如何将视图的 BackgroundColor 属性绑定到 Xamarin Forms 中的视图模型？

Question

So I am making an app in Xamarin Forms, using Fresh MVVM, and I want an event to be executed when a button is pressed, and only if the BackgroundColor of the button is white. The backgroundColor of the button will change in the XAML.CS, while this event will occur in the ViewModel.

The problem is that with the current code that I have the property of my ViewModel has all primary colors and properties set to 0 instead of the actual button color properties. I have already looked for an answer, but nothing helped me.

Here goes the XAML code:

<Button
            x:Name="Button_NextStep"
            HeightRequest="50"
            WidthRequest="400"
            BackgroundColor="{Binding NextStepBackgroundColor}"
            CornerRadius="30"

            Text="Next step"
            TextColor="#4847FF"
            FontAttributes="Bold"
            FontSize="20"

            VerticalOptions="Start"
            HorizontalOptions="Start"
            Margin="25,178,25,5"

            Command="{Binding NextStep}"
></Button>

ViewModel code:

class CreateAccount_UsernameViewModel: FreshBasePageModel
    {
        public ICommand NextStep { get; set; }
        public Color NextStepBackgroundColor { get; set; }

        public InavigationService navigationService; //this is irrelevant for this question

        public CreateAccount_UsernameViewModel(InavigationService _navService)
        {
            navigationService = _navService; //this is irrelevant for this question

            NextStep = new Command(() =>
            {
                if (NextStepBackgroundColor == Color.FromHex("#FFD3D3D3"))
                    navigationService.SwitchNavigationStacks(Enums.NavigationStacks.CreateAccount, this); //this is irrelevant for this question
            });
        }
    }

And that is all, if you need more info to facilitate the solution I will provide it to you as soon as I see your request. Thank you all for your time, hope you have a good day.

Answer 1

Major Binding modes are - ( Expect OneTime and Default(self-explanatory from name ))

1. OneWay = the value change in ViewModel is set to the View(here button). This is the default for most Properties.

2. TwoWay = The Value change in both ViewModel and View gets Notified. This is set to properties that change from the source side, like the Text property of Entry , SelectedItem property of ListView , and so on.

3. OneWayToSource = The value change in View is notified to ViewModel but value change in ViewModel is not notified to the View.

The problem in your scenario is that the BindingMode of BackgroundColor property of Button is OneWay by default, it also does not make sense to keep BindingMode of BackgroundColor of Button as TwoWay as the value is not going to change from the control side.

But the change in BackgroundColor property has to be reflected in ViewModel, Hence BindingMode has to be set to OneWayToSource .