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();
}
}
}