/maui-data-binding

Data Binding API Reference

Binding Modes

BindingContext and Property Paths

• Every BindableObject inherits BindingContext from its parent unless explicitly set.
• Property paths support dot notation and indexers:

<Label Text="{Binding Address.City}" />
<Label Text="{Binding Items[0].Name}" />

• Set BindingContext in XAML or code-behind:

<ContentPage xmlns:vm="clr-namespace:MyApp.ViewModels"
             x:DataType="vm:MainViewModel">
    <ContentPage.BindingContext>
        <vm:MainViewModel />
    </ContentPage.BindingContext>
</ContentPage>

IValueConverter

Implement IValueConverter with Convert (source → target) and ConvertBack (target → source):

public class IntToBoolConverter : IValueConverter
{
    public object? Convert(object? value, Type targetType,
        object? parameter, CultureInfo culture)
        => value is int i && i != 0;

    public object? ConvertBack(object? value, Type targetType,
        object? parameter, CultureInfo culture)
        => value is true ? 1 : 0;
}

Declaring converters in XAML resources

<ContentPage.Resources>
    <local:IntToBoolConverter x:Key="IntToBool" />
</ContentPage.Resources>

<Switch IsToggled="{Binding Count, Converter={StaticResource IntToBool}}" />

ConverterParameter

ConverterParameter is always passed as a string. Parse it inside Convert:

<Label Text="{Binding Score, Converter={StaticResource ThresholdConverter},
              ConverterParameter=50}" />

int threshold = int.Parse((string)parameter);

StringFormat

Use Binding.StringFormat for simple display formatting without a converter:

<Label Text="{Binding Price, StringFormat='Total: {0:C2}'}" />
<Label Text="{Binding DueDate, StringFormat='{0:MMM dd, yyyy}'}" />

Note: Wrap the format string in single quotes when it contains commas or braces.

Multi-Binding

Combine multiple source values with IMultiValueConverter:

<Label>
    <Label.Text>
        <MultiBinding Converter="{StaticResource FullNameConverter}"
                      StringFormat="{}{0}">
            <Binding Path="FirstName" />
            <Binding Path="LastName" />
        </MultiBinding>
    </Label.Text>
</Label>

public class FullNameConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType,
        object parameter, CultureInfo culture)
    {
        if (values.Length == 2 && values[0] is string first && values[1] is string last)
            return $"{first} {last}";
        return string.Empty;
    }

    public object[] ConvertBack(object value, Type[] targetTypes,
        object parameter, CultureInfo culture)
        => throw new NotSupportedException();
}

Relative Bindings

<!-- Square box: Height = Width -->
<BoxView WidthRequest="100"
         HeightRequest="{Binding Source={RelativeSource Self}, Path=WidthRequest}" />

Binding Fallbacks

• FallbackValue – used when the binding path cannot be resolved or the converter throws.
• TargetNullValue – used when the bound value is null.

<Label Text="{Binding MiddleName, TargetNullValue='(none)',
              FallbackValue='unavailable'}" />
<Image Source="{Binding AvatarUrl, TargetNullValue='default_avatar.png'}" />