c# – 带有标记扩展名的字符串格式

我试图使string.Format作为 WPF中的一个方便的函数可用,以便各种文本部分可以在纯XAML中组合,而不需要代码隐藏的样板.主要问题是对函数的参数来自其他嵌套标记扩展(如Binding)的情况的支持.

实际上,有一个非常接近我所需要的功能：MultiBinding.不幸的是,它只能接受绑定,但不能接受其他动态类型的内容,如DynamicResources.

如果我的所有数据源都是绑定的,我可以使用这样的标记：

<TextBlock>
    <TextBlock.Text>
        <MultiBinding Converter="{StaticResource StringFormatConverter}">
            <Binding Path="FormatString"/>
            <Binding Path="Arg0"/>
            <Binding Path="Arg1"/>
            <!-- ... -->
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>

与StringFormatConveter的明显实现.

我试图实现一个自定义的标记扩展,以便语法是这样的：

<TextBlock>
    <TextBlock.Text>
        <l:StringFormat Format="{Binding FormatString}">
            <DynamicResource ResourceKey="ARG0ID"/>
            <Binding Path="Arg1"/>
            <StaticResource ResourceKey="ARG2ID"/>
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>

或者也许只是

<TextBlock Text="{l:StringFormat {Binding FormatString},arg0={DynamicResource ARG0ID},arg1={Binding Arg2},arg2='literal string',...}"/>

但是,对于参数为另一个标记扩展的情况,我坚持执行ProvideValue(IServiceProvider serviceProvider).

互联网中的大多数示例都是微不足道的：他们根本不使用serviceProvider,或者查询IProvideValueTarget,这主要是说标记扩展的目标是什么依赖属性.在任何情况下,代码都知道在ProvideValue调用时应该提供的值.然而,ProvideValue只会被调用一次(except for templates,这是一个单独的故事),所以如果实际值不是常数,就应该使用另外的策略(就像Binding等).

我在Reflector中查找了Binding的实现,它的ProvideValue方法实际上并没有返回真正的目标对象,而是返回System.Windows.Data.BindingExpression类的一个实例,它似乎做了所有的真正的工作.关于DynamicResource也是一样的：它只是返回一个System.Windows.ResourceReferenceExpression的一个实例,该实例关心订阅(内部)InheritanceContextChanged并在适当时使该值无效.然而,我从代码中看不到什么是以下内容：

>如何发生类型BindingExpression / ResourceReferenceExpression的对象不被“按原样”处理,但被要求基础值？
> MultiBindingExpression如何知道底层绑定的值已更改,因此它也必须使其值无效？

我实际上发现了一个标记扩展库实现,声称支持连接字符串(这完全映射到我的用例)(project,code,concatenation implementation依赖于other code),但似乎只支持库类型的嵌套扩展(即,你不能在里面嵌入一个香草Binding).

有没有办法实现问题顶部提出的语法？这是一个受支持的场景,还是只能从WPF框架内部执行此操作(因为System.Windows.Expression有一个内部构造函数)？

实际上,我使用自定义的不可见助手UI元素来实现所需的语义：

<l:FormatHelper x:Name="h1" Format="{DynamicResource FORMAT_ID'">
    <l:FormatArgument Value="{Binding Data1}"/>
    <l:FormatArgument Value="{StaticResource Data2}"/>
</l:FormatHelper>
<TextBlock Text="{Binding Value,ElementName=h1}"/>

(其中FormatHelper跟踪其子项及其依赖属性更新,并将最新结果存储到Value中),但这种语法似乎是丑陋的,我想在视觉树中摆脱帮助项.

最终的目的是为了便于翻译：像15秒直到爆炸一样的UI字符串自然地表示为本地化格式“{0}直到爆炸”(进入ResourceDictionary,当语言改变时将被替换),并绑定到表示时间的VM依赖属性.

更新报告：我尝试使用我可以在互联网上找到的所有信息实现标记扩展.全面实施在这里([1],[2],[3]),这里是核心部分：

var result = new MultiBinding()
{
    Converter = new StringFormatConverter(),Mode = BindingMode.OneWay
};

foreach (var v in values)
{
    if (v is MarkupExtension)
    {
        var b = v as Binding;
        if (b != null)
        {
            result.Bindings.Add(b);
            continue;
        }

        var bb = v as BindingBase;
        if (bb != null)
        {
            targetObjFE.SetBinding(AddBindingTo(targetObjFE,result),bb);
            continue;
        }
    }

    if (v is System.Windows.Expression)
    {
        DynamicResourceExtension mex = null;
        // didn't find other way to check for dynamic resource
        try
        {
            // rrc is a new ResourceReferenceExpressionConverter();
            mex = (MarkupExtension)rrc.ConvertTo(v,typeof(MarkupExtension))
                as DynamicResourceExtension;
        }
        catch (Exception)
        {
        }
        if (mex != null)
        {
            targetObjFE.SetResourceReference(
                    AddBindingTo(targetObjFE,mex.ResourceKey);
            continue;
        }
    }

    // fallback
    result.Bindings.Add(
        new Binding() { Mode = BindingMode.OneWay,Source = v });
}

return result.ProvideValue(serviceProvider);

这似乎适用于嵌套绑定和动态资源,但是尝试将其嵌套在本身中可能失败,因为在这种情况下,从IProvideValueTarget获取的targetObj为null.我试图解决这个问题,将嵌套绑定合并到外部绑定([1a],[2a])(添加多绑定溢出到外部绑定),这可能与嵌套的多绑定和格式扩展一起使用,但仍然使用嵌套的动态资源失败.

有趣的是,当嵌套不同种类的标记扩展时,我在外部扩展中获得Bindings和MultiBindings,但ResourceReferenceExpression代替DynamicResourceExtension.我不知道为什么它不一致(和BindingExpression重构的Binding如何).

更新报告：不幸的是,答案中提出的想法并没有解决问题.也许这证明,标记扩展虽然功能强大,功能多样,但需要WPF团队更多的关注.

无论如何,我感谢参加讨论的任何人.所提出的部分解决方案足够复杂,值得更多的提升.

更新报告：似乎没有很好的解决方案与标记扩展,或至少WPF知识需要创建的水平太深,不实际.

然而,@adabyron有一个改进的想法,这有助于隐藏主机项目中的帮助元素(但是这个价格是将主机的子类化).我会尝试看看是否可以摆脱子类化(使用劫持主机的LogicalChildren的行为,并添加帮助器元素到我的脑海中,灵感来自同一答案的旧版本).

解决方法

看看下面是否适合你.我拿了你在评论中提供的 test case,并稍微扩展,以更好地说明机制.我猜关键是通过在嵌套容器中使用DependencyProperties来保持灵活性.

编辑：我已经用TextBlock的子类替换了混合行为.这增加了DataContext和DynamicResources更容易的连接.

在旁注中,您的项目使用DynamicResources引入条件的方式不是我会推荐的.而是尝试使用viewmodel来建立条件和/或使用触发器.

XAML：

<UserControl x:Class="WpfApplication1.Controls.ExpiryView" xmlns:system="clr-namespace:System;assembly=mscorlib" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
                 xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity"
                 xmlns:props="clr-namespace:WpfApplication1.Properties" xmlns:models="clr-namespace:WpfApplication1.Models"
                 xmlns:h="clr-namespace:WpfApplication1.Helpers" xmlns:c="clr-namespace:WpfApplication1.CustomControls"
                 Background="#FCF197" FontFamily="Segoe UI"
                 TextOptions.TextFormattingMode="Display">    <!-- please notice the effect of this on font fuzzyness -->

    <UserControl.DataContext>
        <models:Expiryviewmodel />
    </UserControl.DataContext>
    <UserControl.Resources>
        <system:String x:Key="ShortOrLongDateFormat">{0:d}</system:String>
    </UserControl.Resources>
    <Grid>
        <StackPanel>
            <c:TextBlockComplex VerticalAlignment="Center" HorizontalAlignment="Center">
                <c:TextBlockComplex.Content>
                    <h:StringFormatContainer StringFormat="{x:Static props:Resources.ExpiryDate}">
                        <h:StringFormatContainer.Values>
                            <h:StringFormatContainer Value="{Binding ExpiryDate}" StringFormat="{DynamicResource ShortOrLongDateFormat}" />
                            <h:StringFormatContainer Value="{Binding SecondsToExpiry}" />
                        </h:StringFormatContainer.Values>
                    </h:StringFormatContainer>
                </c:TextBlockComplex.Content>
            </c:TextBlockComplex>
        </StackPanel>
    </Grid>
</UserControl>

TextBlockComplex：

using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Windows;
using System.Windows.Controls;
using WpfApplication1.Helpers;

namespace WpfApplication1.CustomControls
{
    public class TextBlockComplex : TextBlock
    {
        // Content
        public StringFormatContainer Content { get { return (StringFormatContainer)GetValue(ContentProperty); } set { SetValue(ContentProperty,value); } }
        public static readonly DependencyProperty ContentProperty = DependencyProperty.Register("Content",typeof(StringFormatContainer),typeof(TextBlockComplex),new PropertyMetadata(null));

        private static readonly DependencyPropertyDescriptor _dpdValue = DependencyPropertyDescriptor.FromProperty(StringFormatContainer.ValueProperty,typeof(StringFormatContainer));
        private static readonly DependencyPropertyDescriptor _dpdValues = DependencyPropertyDescriptor.FromProperty(StringFormatContainer.ValuesProperty,typeof(StringFormatContainer));
        private static readonly DependencyPropertyDescriptor _dpdStringFormat = DependencyPropertyDescriptor.FromProperty(StringFormatContainer.StringFormatProperty,typeof(StringFormatContainer));
        private static readonly DependencyPropertyDescriptor _dpdContent = DependencyPropertyDescriptor.FromProperty(TextBlockComplex.ContentProperty,typeof(StringFormatContainer));

        private EventHandler _valueChangedHandler;
        private NotifyCollectionChangedEventHandler _valuesChangedHandler;

        protected override IEnumerator LogicalChildren { get { yield return Content; } }

        static TextBlockComplex()
        {
            // take default style from TextBlock
            DefaultStyleKeyProperty.OverrideMetadata(typeof(TextBlockComplex),new FrameworkPropertyMetadata(typeof(TextBlock)));
        }

        public TextBlockComplex()
        {
            _valueChangedHandler = delegate { AddListeners(this.Content); UpdateText(); };
            _valuesChangedHandler = delegate { AddListeners(this.Content); UpdateText(); };

            this.Loaded += TextBlockComplex_Loaded;
        }

        void TextBlockComplex_Loaded(object sender,RoutedEventArgs e)
        {
            OnContentChanged(this,EventArgs.Empty); // initial call

            _dpdContent.AddValueChanged(this,_valueChangedHandler);
            this.Unloaded += delegate { _dpdContent.RemoveValueChanged(this,_valueChangedHandler); };
        }

        /// <summary>
        /// Reacts to a new topmost StringFormatContainer
        /// </summary>
        private void OnContentChanged(object sender,EventArgs e)
        {
            this.AddLogicalChild(this.Content); // inherits DataContext
            _valueChangedHandler(this,EventArgs.Empty);
        }

        /// <summary>
        /// Updates Text to the Content values
        /// </summary>
        private void UpdateText()
        {
            this.Text = Content.GetValue() as string;
        }

        /// <summary>
        /// Attaches listeners for changes in the Content tree
        /// </summary>
        private void AddListeners(StringFormatContainer cont)
        {
            // in case they have been added before
            RemoveListeners(cont);

            // listen for changes to values collection
            cont.CollectionChanged += _valuesChangedHandler;

            // listen for changes in the bindings of the StringFormatContainer
            _dpdValue.AddValueChanged(cont,_valueChangedHandler);
            _dpdValues.AddValueChanged(cont,_valueChangedHandler);
            _dpdStringFormat.AddValueChanged(cont,_valueChangedHandler);

            // prevent memory leaks
            cont.Unloaded += delegate { RemoveListeners(cont); };

            foreach (var c in cont.Values) AddListeners(c); // recursive
        }

        /// <summary>
        /// Detaches listeners
        /// </summary>
        private void RemoveListeners(StringFormatContainer cont)
        {
            cont.CollectionChanged -= _valuesChangedHandler;

            _dpdValue.RemoveValueChanged(cont,_valueChangedHandler);
            _dpdValues.RemoveValueChanged(cont,_valueChangedHandler);
            _dpdStringFormat.RemoveValueChanged(cont,_valueChangedHandler);
        }
    }
}

StringFormatContainer：

using System.Linq;
using System.Collections;
using System.Collections.ObjectModel;
using System.Windows;

namespace WpfApplication1.Helpers
{
    public class StringFormatContainer : FrameworkElement
    {
        // Values
        private static readonly DependencyPropertyKey ValuesPropertyKey = DependencyProperty.RegisterReadOnly("Values",typeof(ObservableCollection<StringFormatContainer>),new FrameworkPropertyMetadata(new ObservableCollection<StringFormatContainer>()));
        public static readonly DependencyProperty ValuesProperty = ValuesPropertyKey.DependencyProperty;
        public ObservableCollection<StringFormatContainer> Values { get { return (ObservableCollection<StringFormatContainer>)GetValue(ValuesProperty); } }

        // StringFormat
        public static readonly DependencyProperty StringFormatProperty = DependencyProperty.Register("StringFormat",typeof(string),new PropertyMetadata(default(string)));
        public string StringFormat { get { return (string)GetValue(StringFormatProperty); } set { SetValue(StringFormatProperty,value); } }

        // Value
        public static readonly DependencyProperty ValueProperty = DependencyProperty.Register("Value",typeof(object),new PropertyMetadata(default(object)));
        public object Value { get { return (object)GetValue(ValueProperty); } set { SetValue(ValueProperty,value); } }

        public StringFormatContainer()
            : base()
        {
            SetValue(ValuesPropertyKey,new ObservableCollection<StringFormatContainer>());
            this.Values.CollectionChanged += OnValuesChanged;
        }

        /// <summary>
        /// The implementation of LogicalChildren allows for DataContext propagation.
        /// This way,the DataContext needs only be set on the outermost instance of StringFormatContainer.
        /// </summary>
        void OnValuesChanged(object sender,System.Collections.Specialized.NotifyCollectionChangedEventArgs e)
        {
            if (e.NewItems != null)
            {
                foreach (var value in e.NewItems)
                    AddLogicalChild(value);
            }
            if (e.OldItems != null)
            {
                foreach (var value in e.OldItems)
                    RemoveLogicalChild(value);
            }
        }

        /// <summary>
        /// Recursive function to piece together the value from the StringFormatContainer hierarchy
        /// </summary>
        public object GetValue()
        {
            object value = null;
            if (this.StringFormat != null)
            {
                // convention: if StringFormat is set,Values take precedence over Value
                if (this.Values.Any())
                    value = string.Format(this.StringFormat,this.Values.Select(v => (object)v.GetValue()).ToArray());
                else if (Value != null)
                    value = string.Format(this.StringFormat,Value);
            }
            else
            {
                // convention: if StringFormat is not set,Value takes precedence over Values
                if (Value != null)
                    value = Value;
                else if (this.Values.Any())
                    value = string.Join(string.Empty,this.Values);
            }
            return value;
        }

        protected override IEnumerator LogicalChildren
        {
            get
            {
                if (Values == null) yield break;
                foreach (var v in Values) yield return v;
            }
        }
    }
}

Expiryviewmodel：

using System;
using System.ComponentModel;

namespace WpfApplication1.Models
{
    public class Expiryviewmodel : INotifyPropertyChanged
    {
        public event PropertyChangedEventHandler PropertyChanged;
        protected void OnPropertyChanged(string propertyName)
        {
            if (this.PropertyChanged != null)
                PropertyChanged(this,new PropertyChangedEventArgs(propertyName));
        }

        private DateTime _expiryDate;
        public DateTime ExpiryDate { get { return _expiryDate; } set { _expiryDate = value; OnPropertyChanged("ExpiryDate"); } }

        public int SecondsToExpiry { get { return (int)ExpiryDate.Subtract(DateTime.Now).TotalSeconds; } }

        public Expiryviewmodel()
        {
            this.ExpiryDate = DateTime.Today.AddDays(2.67);

            var timer = new System.Timers.Timer(1000);
            timer.Elapsed += (s,e) => OnPropertyChanged("SecondsToExpiry");
            timer.Start();
        }
    }
}

原文链接：https://www.f2er.com/csharp/97241.html

c# – 带有标记扩展名的字符串格式

解决方法

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