Advanced Binding Options

Introduction

Gum provides multiple options to control how binding behaves using the Binding type.

Using the Binding Class

The fastest way to set up binding is to use the name of the properties being bound, as shown in the following code example:

label.SetBinding(
    // UI property:
    nameof(label.Text),

    // ViewModel property:
    nameof(MyViewModel.LabelText));

The SetBinding call shown above is a shortcut for creating a Binding object. The following code is functionally identical:

// Binding is created using the ViewModel property
Binding binding = new(nameof(MyViewModel.LabelText));
label.SetBinding(
    // UI property:
    nameof(label.Text),
    binding);

The Binding instance can be modified by setting its properties on initializers. For example the following code shows how to update the binding to be one-way from the source (ViewModel) to the target (Label):

Binding binding = new(nameof(MyViewModel.LabelText))
{
    Mode = BindingMode.OneWay
};

label.SetBinding(
    nameof(label.Text),
    binding);

Available Binding Properties

The following properties are available on the Binding class. Note that the term "source" typically refers to the ViewModel:

• Path - the property name on the source, such as LabelText

• Mode - the direction of data flow in binding. This can be used to create one-way binding.

• UpdateSourceTrigger - controls when binding is applied

• FallbackValue - the value to apply when when binding cannot retrieve a value from the source

• TargetNullValue - Gets or sets the value to use when the source property value is null

• Converter - Gets or sets a converter to transform values between the source and target

• ConverterParameter - Gets or sets an optional parameter to pass to the Converter

• StringFormat - Gets or sets a format string to apply to the value