如何在 .Net 4.0 中实现 .Net 4.5 的延迟属性(描述 here)？

我知道我无法从 BindingBase 继承，因为 ProvideValue 是密封的。

我可以实现 MarkupExtension，但这意味着我现在必须重写 BindingExtension 的所有属性，还有其他方法吗？

最佳答案

最后，我决定使用组合将 DelayedBinding 实现为 MarkupExtension。

我遇到的唯一问题是如果 IProvideValueTarget 中的 TargetProperty 为 null，DataTemplates ProvideValue 应该返回此值。

[MarkupExtensionReturnType(typeof(object))]
public class DelayedBindingExtension : MarkupExtension
{
    private readonly Binding _binding = new Binding();

    public DelayedBindingExtension()
    {
        //Default value for delay
        Delay = TimeSpan.FromSeconds(0.5);
    }

    public DelayedBindingExtension(PropertyPath path)
        : this()
    {
        Path = path;
    }

    #region properties

    [DefaultValue(null)]
    public object AsyncState
    {
        get { return _binding.AsyncState; }
        set { _binding.AsyncState = value; }
    }

    [DefaultValue(false)]
    public bool BindsDirectlyToSource
    {
        get { return _binding.BindsDirectlyToSource; }
        set { _binding.BindsDirectlyToSource = value; }
    }

    [DefaultValue(null)]
    public IValueConverter Converter
    {
        get { return _binding.Converter; }
        set { _binding.Converter = value; }
    }

    [TypeConverter(typeof(CultureInfoIetfLanguageTagConverter)), DefaultValue(null)]
    public CultureInfo ConverterCulture
    {
        get { return _binding.ConverterCulture; }
        set { _binding.ConverterCulture = value; }
    }

    [DefaultValue(null)]
    public object ConverterParameter
    {
        get { return _binding.ConverterParameter; }
        set { _binding.ConverterParameter = value; }
    }

    [DefaultValue(null)]
    public string ElementName
    {
        get { return _binding.ElementName; }
        set { _binding.ElementName = value; }
    }

    [DefaultValue(null)]
    public object FallbackValue
    {
        get { return _binding.FallbackValue; }
        set { _binding.FallbackValue = value; }
    }

    [DefaultValue(false)]
    public bool IsAsync
    {
        get { return _binding.IsAsync; }
        set { _binding.IsAsync = value; }
    }

    [DefaultValue(BindingMode.Default)]
    public BindingMode Mode
    {
        get { return _binding.Mode; }
        set { _binding.Mode = value; }
    }

    [DefaultValue(false)]
    public bool NotifyOnSourceUpdated
    {
        get { return _binding.NotifyOnSourceUpdated; }
        set { _binding.NotifyOnSourceUpdated = value; }
    }

    [DefaultValue(false)]
    public bool NotifyOnTargetUpdated
    {
        get { return _binding.NotifyOnTargetUpdated; }
        set { _binding.NotifyOnTargetUpdated = value; }
    }

    [DefaultValue(false)]
    public bool NotifyOnValidationError
    {
        get { return _binding.NotifyOnValidationError; }
        set { _binding.NotifyOnValidationError = value; }
    }

    [DefaultValue(null)]
    public PropertyPath Path
    {
        get { return _binding.Path; }
        set { _binding.Path = value; }
    }

    [DefaultValue(null)]
    public RelativeSource RelativeSource
    {
        get { return _binding.RelativeSource; }
        set { _binding.RelativeSource = value; }
    }

    [DefaultValue(null)]
    public object Source
    {
        get { return _binding.Source; }
        set { _binding.Source = value; }
    }

    [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden)]
    public UpdateSourceExceptionFilterCallback UpdateSourceExceptionFilter
    {
        get { return _binding.UpdateSourceExceptionFilter; }
        set { _binding.UpdateSourceExceptionFilter = value; }
    }

    [DefaultValue(UpdateSourceTrigger.Default)]
    public UpdateSourceTrigger UpdateSourceTrigger
    {
        get { return _binding.UpdateSourceTrigger; }
        set { _binding.UpdateSourceTrigger = value; }
    }

    [DefaultValue(null)]
    public object TargetNullValue
    {
        get { return _binding.TargetNullValue; }
        set { _binding.TargetNullValue = value; }
    }

    [DefaultValue(null)]
    public string StringFormat
    {
        get { return _binding.StringFormat; }
        set { _binding.StringFormat = value; }
    }

    [DefaultValue(false)]
    public bool ValidatesOnDataErrors
    {
        get { return _binding.ValidatesOnDataErrors; }
        set { _binding.ValidatesOnDataErrors = value; }
    }

    [DefaultValue(false)]
    public bool ValidatesOnExceptions
    {
        get { return _binding.ValidatesOnExceptions; }
        set { _binding.ValidatesOnExceptions = value; }
    }

    [DefaultValue(null)]
    public string XPath
    {
        get { return _binding.XPath; }
        set { _binding.XPath = value; }
    }

    [DefaultValue(null)]
    public Collection<ValidationRule> ValidationRules
    {
        get { return _binding.ValidationRules; }
    }

    #endregion

    [DefaultValue(null)]
    public TimeSpan Delay { get; set; }

    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        try
        {
            _binding.Mode = BindingMode.TwoWay;
            _binding.UpdateSourceTrigger = UpdateSourceTrigger.Explicit;
        }
        catch (InvalidOperationException)  //Binding in use already don't change it
        {
        }

        var valueProvider = serviceProvider.GetService(typeof (IProvideValueTarget)) as IProvideValueTarget;
        if (valueProvider != null)
        {
            var bindingTarget = valueProvider.TargetObject as DependencyObject;
            var bindingProperty = valueProvider.TargetProperty as DependencyProperty;
            if (bindingProperty != null && bindingTarget != null)
            {
                var result = (BindingExpression)_binding.ProvideValue(serviceProvider);

                new DelayBindingManager(result, bindingTarget, bindingProperty, Delay);
                return result;
            }
        }

        return this;
    }

    private class DelayBindingManager
    {
        private readonly BindingExpressionBase _bindingExpression;
        private readonly DependencyProperty _bindingTargetProperty;
        private DependencyPropertyDescriptor _descriptor;
        private readonly DispatcherTimer _timer;

        public DelayBindingManager(BindingExpressionBase bindingExpression, DependencyObject bindingTarget, DependencyProperty bindingTargetProperty, TimeSpan delay)
        {
            _bindingExpression = bindingExpression;
            _bindingTargetProperty = bindingTargetProperty;

            _descriptor = DependencyPropertyDescriptor.FromProperty(_bindingTargetProperty, bindingTarget.GetType());
            if (_descriptor != null)
                _descriptor.AddValueChanged(bindingTarget, BindingTargetTargetPropertyChanged);

            _timer = new DispatcherTimer();
            _timer.Tick += TimerTick;
            _timer.Interval = delay;
        }

        private void BindingTargetTargetPropertyChanged(object sender, EventArgs e)
        {
            var source = (DependencyObject)sender;
            if (!BindingOperations.IsDataBound(source, _bindingTargetProperty))
            {
                if (_descriptor != null)
                {
                    _descriptor.RemoveValueChanged(source, BindingTargetTargetPropertyChanged);
                    _descriptor = null;
                }
                return;
            }

            _timer.Stop();
            _timer.Start();
        }

        private void TimerTick(object sender, EventArgs e)
        {
            _timer.Stop();
            _bindingExpression.UpdateSource();
        }
    }
}

关于c# - 在 .Net 4.0 中从 .Net 4.5 绑定(bind)的延迟属性，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/7661149/