Avalonia/src/Markup/Avalonia.Markup/Data/BindingBase.cs

using System;
using System.ComponentModel;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using Avalonia.Controls;
using Avalonia.Data.Converters;
using Avalonia.Data.Core;
using Avalonia.Diagnostics;

namespace Avalonia.Data
{
    public abstract class BindingBase : IBinding, IBinding2
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="Binding"/> class.
        /// </summary>
        public BindingBase()
        {
            FallbackValue = AvaloniaProperty.UnsetValue;
            TargetNullValue = AvaloniaProperty.UnsetValue;
        }

        /// <summary>
        /// Initializes a new instance of the <see cref="Binding"/> class.
        /// </summary>
        /// <param name="mode">The binding mode.</param>
        public BindingBase(BindingMode mode = BindingMode.Default)
            :this()
        {
            Mode = mode;
        }

        /// <summary>
        /// Gets or sets the <see cref="IValueConverter"/> to use.
        /// </summary>
        public IValueConverter? Converter { get; set; }

        /// <summary>
        /// Gets or sets the culture in which to evaluate the converter.
        /// </summary>
        /// <value>The default value is null.</value>
        /// <remarks>
        /// If this property is not set then <see cref="CultureInfo.CurrentCulture"/> will be used.
        /// </remarks>
        [TypeConverter(typeof(CultureInfoIetfLanguageTagConverter))]
        public CultureInfo? ConverterCulture { get; set; }

        /// <summary>
        /// Gets or sets a parameter to pass to <see cref="Converter"/>.
        /// </summary>
        public object? ConverterParameter { get; set; }

        /// <summary>
        /// Gets or sets the value to use when the binding is unable to produce a value.
        /// </summary>
        public object? FallbackValue { get; set; }

        /// <summary>
        /// Gets or sets the value to use when the binding result is null.
        /// </summary>
        public object? TargetNullValue { get; set; }

        /// <summary>
        /// Gets or sets the binding mode.
        /// </summary>
        public BindingMode Mode { get; set; }

        /// <summary>
        /// Gets or sets the binding priority.
        /// </summary>
        public BindingPriority Priority { get; set; }

        /// <summary>
        /// Gets or sets the string format.
        /// </summary>
        public string? StringFormat { get; set; }

        public WeakReference? DefaultAnchor { get; set; }

        public WeakReference<INameScope?>? NameScope { get; set; }

        /// <inheritdoc/>
        [UnconditionalSuppressMessage("Trimming", "IL2026", Justification = TrimmingMessages.TypeConversionSupressWarningMessage)]
        [Obsolete(ObsoletionMessages.MayBeRemovedInAvalonia12)]
        public abstract InstancedBinding? Initiate(
            AvaloniaObject target,
            AvaloniaProperty? targetProperty,
            object? anchor = null,
            bool enableDataValidation = false);

        private protected abstract BindingExpressionBase Instance(AvaloniaProperty targetProperty, AvaloniaObject target);

        private protected BindingMode ResolveBindingMode(AvaloniaObject target, AvaloniaProperty? targetProperty)
        {
            if (Mode != BindingMode.Default)
                return Mode;
            if (targetProperty is null)
                return BindingMode.OneWay;
            return targetProperty.GetMetadata(target.GetType()).DefaultBindingMode;
        }

        BindingExpressionBase IBinding2.Instance(AvaloniaObject target, AvaloniaProperty property) => Instance(property, target);
    }
}