Binding Custom View Properties

Introduction

Binding in Gum supports binding to built-in properties as well as custom properties. This page shows how to perform binding on custom properties.

Custom Properties in Controls

Custom properties are typically added to views to control additional visuals. For example, a button may have a TextRuntime subtext, and its Text property might be exposed through a property as is shown in the following code:

using Gum.Forms.Controls;
using Gum.Forms.DefaultVisuals.V3;
using Microsoft.Xna.Framework;
using MonoGameGum.GueDeriving;
using System;

namespace MonoGameAndGum;

public class ButtonWithSubtext : Button
{
    TextRuntime _textRuntime;

    public string Subtext
    {
        get => _textRuntime.Text;
        set
        {
            if (_textRuntime.Text != value)
            {
                _textRuntime.Text = value;
            }
        }
    }

    public ButtonWithSubtext() : base()
    {
        ButtonVisual visual = (ButtonVisual)Visual;

        _textRuntime = new TextRuntime();
        this.AddChild(_textRuntime);
        _textRuntime.Anchor(Gum.Wireframe.Anchor.Center);
        _textRuntime.Y = 20;
        _textRuntime.Color = Color.Yellow;
    }
}

An instance of this view could be created using the following code:

ButtonWithSubtext button = new ();
button.AddToRoot();
button.Anchor(Anchor.Center);
button.Text = "Click me please";
button.Subtext = "0 clicks";

Although this property is a standard C# property, it can be (one way) bound with no additional code on the view. This makes binding very easy since it does not require the creation of a dependency property.

The following code shows how to create a view model, and bind the Subtext property:

class ExampleViewModel : ViewModel
{
    public int NumberOfClicks
    {
        get => Get<int>();
        set => Set(value);
    }

    [DependsOn(nameof(NumberOfClicks))]
    public string ClicksDisplay => $"{NumberOfClicks} click(s)";
}

protected override void Initialize()
{
    // either one of these:
    //GumUI.Initialize(this, "GumProject/GumProject.gumx");
    GumUI.Initialize(this, Gum.Forms.DefaultVisualsVersion.Newest);

    ButtonWithSubtext button = new ();
    button.AddToRoot();
    button.Anchor(Anchor.Center);
    button.Text = "Click me please";

    ExampleViewModel viewModel = new ();
    button.BindingContext = viewModel;
    button.SetBinding(
        nameof(button.Subtext),
        nameof(viewModel.ClicksDisplay));

    button.Click += (not, used) => 
    {
        viewModel.NumberOfClicks++;
    };

    base.Initialize();
}

Button responding to clicks and updating itself through the ViewModel