How to bind?

[PlayCreatively]

I was trying to bind a label's TextProperty to the page's local string (just to see how binding works and get the ball rolling), but I'm not able to make it bind.

This is the code I've written and I've tried all kinds of different variations of this but non work, so clearly I don't understand how binding works. However, I haven't found any info on the internet on how to make this simple binding. I've only seen people use an event handler or the sample code here which I'm trying to immitate, but evidently failing. Can someone explain this for me? 🙏

class MyPage : ContentPage
    {
        public string myVal = "initial value";
        public DataPage()
        {
            Content =
                new VerticalStackLayout()
                {
                    Children = 
                    { 
                        new Label().Bind(Label.TextProperty, path: nameof(MyPage.myVal), source: this)
                    }
                };
        }
    }

[bijington]

Hey @PlayCreatively,

We do link over to the .NET MAUI docs but I don't actually see anything clearly helpful there either. Essentially when creating a binding we need to do so against a property that is accessible (public or internal), to tell the control the context of the binding (BindingContext) and we also need a way of notifying the control when things change (INotifyPropertyChanged).

What you had was close but there are some extra bits you needed. See this modified version of your code:

class MyPage : ContentPage
{
    public string MyVal { get; } = "initial value";

    public DataPage()
    {
        BindingContext = this;

        Content =
            new VerticalStackLayout()
            {
                Children = 
                { 
                    new Label().Bind(Label.TextProperty, path: nameof(MyPage.MyVal))
                }
            };
    }
}

The changes I made are:

1. Set the BindingContext on the page to itself to know where the binding comes from.
2. Changed your field myVar to a property MyVar
3. I haven't added the notification of changes as you don't need it in this example and it adds more noise to getting this sample working. I can add that separately if you need

[PlayCreatively]

I haven't added the notification of changes as you don't need it in this example and it adds more noise to getting this sample working. I can add that separately if you need

I would actually love it if you could maybe bind the Label to an Entry so I can see how it works.

How I understand how it works is that when a View has an INotifyPropertyChanged interface the XAML subscribes to it automatically when you bind it through XAML, but since I'm not using XAML I'll have to do it manually, I'm guessing 🤔

[bijington]

Oh if you are binding two controls together you can actually ignore my point about INotifyPropertyChanged we use this when one side of the binding needs to trigger the updates which is typically implemented in a View Model, the controls themselves already handle the updates for you.

If you wanted to bind your Label to an Entry you can do something like:

class MyPage : ContentPage
{
    public DataPage()
    {
        Content =
            new VerticalStackLayout()
            {
                Children = 
                { 
                    new Entry().Assign(out var myEntry),

                    new Label()
                      .Bind(
                        Label.TextProperty,
                        path: nameof(Entry.Text),
                        source: myEntry)
                }
            };
    }
}

This is binding the TextProperty of your Label to the Text property on your Entry called myEntry.

The Assign method is another extension that we provide to allow you to keep creating the UI fluently but assign it out to a variable for use later on, more documentation here

[CliffAgius]

Closed and answered