Data binding to visibility of button from ViewModel

StephenHarris · September 2016

I have a ContentPage that is binded to a ViewModel and I want to update the visibility of a button from the ViewModel. If I remove the Path, the binding works, but it doesn't update in the view when I change it in the viewModel. With the Path set, nothing seems to work. Does anyone have any experience doing this in code as opposed to xaml? Here is what I have so far.

From viewModel:

public bool DoneIsAvailable { get { return _doneIsAvailable; } set { _doneIsAvailable = value; OnPropertyChanged("ShowDone"); } }

And here from the ContentPage

            var doneButton = new Button
                {
                    BackgroundColor = Color.Gray,
                    Text = "Done",
                    TextColor = Color.Blue,
                    FontSize = 15,
                    Command = viewModel.DoneButton
                };

                Binding doneBinding = new Binding
                {
                    Source = viewModel.DoneIsAvailable,
                    Path = "ShowDone",
                    Mode = BindingMode.OneWay,
                };
                doneButton.SetBinding(IsVisibleProperty, doneBinding);

JoeManke · October 2016

The name of the property you're binding to and the name you pass into OnPropertyChanged must be the same. The nameof operator is extremely useful for this, or if your implementation of OnPropertyChanged uses the [CallerMemberName] attribute for its parameter you don't even need to pass anything in when you call it from a setter. (BindableObject has this attribute.)

ViewModel:

public bool DoneIsAvailable
{
    get
    {
        return _doneIsAvailable;
    }
    set
    {
        _doneIsAvailable = value;
        OnPropertyChanged(nameof(DoneIsAvailable);
    }
}

Page:

doneButton.SetBinding(IsVisibleProperty, nameof(viewModel.DoneIsAvailable));

StephenHarris · October 2016

I still would like to know the correct way to get this binding to update but, I was able to work-around this issue by creating a button in my viewModel and referencing it in my view. Then when I dynamically updated the button in my viewModel, it also updated in my view.

NMackay · October 2016

@StephenHarris

Try changing the binding mode to BindingMode.TwoWay.

JoeManke · October 2016

The name of the property you're binding to and the name you pass into OnPropertyChanged must be the same. The nameof operator is extremely useful for this, or if your implementation of OnPropertyChanged uses the [CallerMemberName] attribute for its parameter you don't even need to pass anything in when you call it from a setter. (BindableObject has this attribute.)

ViewModel:

public bool DoneIsAvailable
{
    get
    {
        return _doneIsAvailable;
    }
    set
    {
        _doneIsAvailable = value;
        OnPropertyChanged(nameof(DoneIsAvailable);
    }
}

Page:

doneButton.SetBinding(IsVisibleProperty, nameof(viewModel.DoneIsAvailable));

StephenHarris · October 2016

You nailed it JoeManke! I made sure the property name was the same name I passed to OnPropertyChanged and used the nameof operator. It works like it's supposed to. Thank you very much!

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