c# - WPF 中 DisplayFormatAttribute 的推荐替代方法是什么？

Question

所以我找到了 DisplayFormatAttribute 类(我猜它只用于 Web 开发？)。它确实会在可维护性方面改进我的项目，因为我有许多小数属性，它们的小数位数似乎一次又一次地改变(客户要求与我的“聪明”想法混合在一起)。

基本上，我会有这样的属性:

[DisplayFormat(DataFormatString = "{0:n4} %")]
public decimal Nh3 {get; set;}

如 DisplayFormatAttribute 所示，需要在当前用户语言环境中显示四位小数，后跟一个 %。

在 XAML 中我会有类似的东西

<TextBlock Text="{Binding Nh3}"/>

但对于像 0.123456 这样的值，它将显示 0.123456 而对于像 0.12 这样的值，它将显示 0.12。我需要它分别显示 0.1235 % 和 0.1200 %。

对于特定的 TextBlock，这可以通过

实现

<TextBlock Text="{Binding Nh3, StringFormat={}{0:n4} %"/>

但正如我提到的那样，这是重复且容易出错的。

我见过有人用类似的东西

<TextBlock Text="{Binding Nh3, StringFormat={StaticResource Nh3Format} %"/>

但我发现这相当复杂(与 Nh3 属性上的属性相比)。但我希望有人能以更好的方式帮助我解决这个问题。

Answer 1

您可以定义自己的 DisplayFormatAttribute 和 custom markup-extension自动为您创建这些绑定(bind)。

///Custom attribute
[AttributeUsageAttribute(AttributeTargets.Property, AllowMultiple = false)]
public class DisplayFormatAttribute : Attribute
{
    public string DataFormatString { get; set; }
}

///Custom markup extension
[ContentProperty("ResourceKey")]
[MarkupExtensionReturnType(typeof(object))]
public class FormattedBindingExtension : MarkupExtension
{
    public FormattedBindingExtension()
    {
    }

    public FormattedBindingExtension(PropertyPath path)
    {
        Path = path;
    }

    public IValueConverter Converter { get; set; }
    public object ConverterParamter { get; set; }

    [ConstructorArgument("path")]
    public PropertyPath Path { get; set; }

    [TypeConverter(typeof(CultureInfoIetfLanguageTagConverter))]
    public CultureInfo ConverterCulture { get; set; }

    private DependencyProperty _bindingTargetProperty;
    public override object ProvideValue(IServiceProvider serviceProvider)
    {
        var valueProvider = serviceProvider.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
        if (valueProvider != null)
        {
            var bindingTarget = valueProvider.TargetObject as DependencyObject;
            var bindingTargetProperty = valueProvider.TargetProperty as DependencyProperty;
            if (bindingTargetProperty == null || bindingTarget == null || Path == null)
            {
                throw new NotSupportedException(string.Format(
                    "The property '{0}' on target '{1}' is not valid for a FormattedBinding. The FormattedBinding target must be a DependencyObject, "
                    + "and the target property must be a DependencyProperty, and a Path must be specified.",
                    valueProvider.TargetProperty,
                    valueProvider.TargetObject));
            }

            // Add support so that the datacontext change causes an immediate commit with format
            var frameworkElement = bindingTarget as FrameworkElement;
            if (frameworkElement != null)
            {
                frameworkElement.DataContextChanged += FrameworkElement_DataContextChanged;
            }

            _bindingTargetProperty = bindingTargetProperty;
            FrameworkElement_DataContextChanged(frameworkElement, new DependencyPropertyChangedEventArgs());

            // Return the current value of the binding (since it will have been evaluated because of the binding above)
            return bindingTarget.GetValue(bindingTargetProperty);
        }
        return null;
    }

    private void FrameworkElement_DataContextChanged(object sender, DependencyPropertyChangedEventArgs ignored)
    {
        var element = sender as FrameworkElement;
        if (element == null || element.DataContext == null)
            return;

        var propertyName = Path.Path;
        if (propertyName == null)
            return;

        var source = element.DataContext;
        var type = source.GetType();

        var property = type.GetProperty(propertyName);
        var format = property.GetCustomAttribute<DisplayFormatAttribute>()?.DataFormatString;
        Binding binding = GetBinding(format);

        // Apply and evaluate the binding
        var bindingExpression = BindingOperations.SetBinding(element, _bindingTargetProperty, binding);
        bindingExpression.UpdateTarget();
    }

    private Binding GetBinding(string format)
    {
        var binding = new Binding();
        binding.Path = Path;
        binding.Converter = Converter;
        binding.ConverterCulture = ConverterCulture;
        binding.ConverterParameter = ConverterParamter;
        binding.StringFormat = format;
        return binding;
    }
}

示例用法:

XAML

<TextBlock Text="{local:FormattedBinding Path=Nh3}"  />

<!-- specify price US currency -->
<TextBlock Text="{local:FormattedBinding Path=Price, ConverterCulture='en-US'}" />

<!-- specify price German currency -->
<TextBlock Text="{local:FormattedBinding Path=Price, ConverterCulture='de-DE'}" />

<!-- specify price Japanese currency -->
<TextBlock Text="{local:FormattedBinding Path=Price, ConverterCulture='ja-JP'}" />

<TextBlock Text="{local:FormattedBinding Path=Today}" />

ViewModel 属性

[DisplayFormat(DataFormatString = "{0:n4} %")]
public double Nh3 { get; set; }

[DisplayFormat(DataFormatString = "{0:C}")]
public decimal Price { get; set; }

[DisplayFormat(DataFormatString = "{0:dddd, MMMM dd}")]
public DateTime Today { get; set; }