/// <inheritdoc/>
public InstancedBinding Initiate(
IAvaloniaObject target,
AvaloniaProperty targetProperty,
object?anchor = null,
bool enableDataValidation = false)
{
_ = target ?? throw new ArgumentNullException(nameof(target));
anchor = anchor ?? DefaultAnchor?.Target;
enableDataValidation = enableDataValidation && Priority == BindingPriority.LocalValue;
var observer = CreateExpressionObserver(target, targetProperty, anchor, enableDataValidation);
var fallback = FallbackValue;
// If we're binding to DataContext and our fallback is UnsetValue then override
// the fallback value to null, as broken bindings to DataContext must reset the
// DataContext in order to not propagate incorrect DataContexts to child controls.
// See Avalonia.Markup.UnitTests.Data.DataContext_Binding_Should_Produce_Correct_Results.
if (targetProperty == StyledElement.DataContextProperty && fallback == AvaloniaProperty.UnsetValue)
{
fallback = null;
}
var converter = Converter;
var targetType = targetProperty?.PropertyType ?? typeof(object);
// We only respect `StringFormat` if the type of the property we're assigning to will
// accept a string. Note that this is slightly different to WPF in that WPF only applies
// `StringFormat` for target type `string` (not `object`).
if (!string.IsNullOrWhiteSpace(StringFormat) &&
(targetType == typeof(string) || targetType == typeof(object)))
{
converter = new StringFormatValueConverter(StringFormat, converter);
}
var subject = new BindingExpression(
observer,
targetType,
fallback,
TargetNullValue,
converter ?? DefaultValueConverter.Instance,
ConverterParameter,
Priority);
return(new InstancedBinding(subject, Mode, Priority));
}
/// <inheritdoc/>
public InstancedBinding Initiate(
IAvaloniaObject target,
AvaloniaProperty targetProperty,
object anchor = null,
bool enableDataValidation = false)
{
Contract.Requires <ArgumentNullException>(target != null);
anchor = anchor ?? DefaultAnchor?.Target;
enableDataValidation = enableDataValidation && Priority == BindingPriority.LocalValue;
ExpressionObserver observer;
var(node, mode) = ExpressionObserverBuilder.Parse(Path, enableDataValidation, TypeResolver);
if (ElementName != null)
{
observer = CreateElementObserver(
(target as IStyledElement) ?? (anchor as IStyledElement),
ElementName,
node);
}
else if (Source != null)
{
observer = CreateSourceObserver(Source, node);
}
else if (RelativeSource == null)
{
if (mode == SourceMode.Data)
{
observer = CreateDataContextObserver(
target,
node,
targetProperty == StyledElement.DataContextProperty,
anchor);
}
else
{
observer = new ExpressionObserver(
(target as IStyledElement) ?? (anchor as IStyledElement),
node);
}
}
else if (RelativeSource.Mode == RelativeSourceMode.DataContext)
{
observer = CreateDataContextObserver(
target,
node,
targetProperty == StyledElement.DataContextProperty,
anchor);
}
else if (RelativeSource.Mode == RelativeSourceMode.Self)
{
observer = CreateSourceObserver(
(target as IStyledElement) ?? (anchor as IStyledElement),
node);
}
else if (RelativeSource.Mode == RelativeSourceMode.TemplatedParent)
{
observer = CreateTemplatedParentObserver(
(target as IStyledElement) ?? (anchor as IStyledElement),
node);
}
else if (RelativeSource.Mode == RelativeSourceMode.FindAncestor)
{
if (RelativeSource.Tree == TreeType.Visual && RelativeSource.AncestorType == null)
{
throw new InvalidOperationException("AncestorType must be set for RelativeSourceMode.FindAncestor when searching the visual tree.");
}
observer = CreateFindAncestorObserver(
(target as IStyledElement) ?? (anchor as IStyledElement),
RelativeSource,
node);
}
else
{
throw new NotSupportedException();
}
var fallback = FallbackValue;
// If we're binding to DataContext and our fallback is UnsetValue then override
// the fallback value to null, as broken bindings to DataContext must reset the
// DataContext in order to not propagate incorrect DataContexts to child controls.
// See Avalonia.Markup.UnitTests.Data.DataContext_Binding_Should_Produce_Correct_Results.
if (targetProperty == StyledElement.DataContextProperty && fallback == AvaloniaProperty.UnsetValue)
{
fallback = null;
}
var converter = Converter;
var targetType = targetProperty?.PropertyType ?? typeof(object);
// We only respect `StringFormat` if the type of the property we're assigning to will
// accept a string. Note that this is slightly different to WPF in that WPF only applies
// `StringFormat` for target type `string` (not `object`).
if (!string.IsNullOrWhiteSpace(StringFormat) &&
(targetType == typeof(string) || targetType == typeof(object)))
{
converter = new StringFormatValueConverter(StringFormat, converter);
}
var subject = new BindingExpression(
observer,
targetType,
fallback,
converter ?? DefaultValueConverter.Instance,
ConverterParameter,
Priority);
return(new InstancedBinding(subject, Mode, Priority));
}
