Silverlight XAML TextBlock当前日期 [英] Current Date in Silverlight XAML TextBlock

问题描述

我来自于Flex，你可以在大括号内做任何事情。我试图获得一个 TextBlock 来显示今天的日期和时间，而不用在C＃中编码它。我尝试了许多不同的变化，没有运气。

  TextBlock Text ={Source = Date，Path = Now，StringFormat ='dd / MM / yyyy'}
  

我知道我可能只需要设置一个属性 MyDate 并绑定到那个，但为什么我不能直接绑定到 DateTime.Now 属性？

解决方案

Silverlight中的绑定需要一个Source对象或一个Dependency对象。从该源对象可以绑定到属性（因此根据定义绑定到实例成员）或依赖属性。

由于 DateTime.Now 是一个静态属性，您不能直接在Silverlight中绑定它，因此需要一些代码。最好的办法是使用代码： -

• 确保您可以在XAML中表达所需的许多


• 以尽可能的解耦方式执行此操作。

因此，我们可以分析我们需要两个

1. 将DateTime的静态成员作为某个对象的实例属性


2. 有一些方法将DateTime格式化为所需的输出。

要处理第一个项目，我将创建一个 StaticSurrogate class，我将为我们需要访问的静态属性创建实例属性： -

  public class StaticSurrogate 
 {
 public DateTime Today {get {return DateTime.Today; }} 
 public DateTime Now {get {return DateTime.Now; }} 
} 
  

现在我们需要一种格式化日期时间的方法。价值转换器是这项工作的正确工具，大量借鉴了这个 Tim Heuer Blog ： -

  public class FormatConverter：IValueConverter 
 {
 public object Convert（object value，Type targetType，object parameter，System.Globalization.CultureInfo culture）
 {
 if（parameter！= null）
 {
 string formatterString = parameter.ToString（）; 
 
 if（！String.IsNullOrEmpty（formatterString））
 {
 return String.Format（culture，String.Format（{{0：{0}}}， formatterString），value）; 
} 
} 
 
 return（value ??）.ToString（）; 
 
 
 public object ConvertBack（object value，Type targetType，object parameter，System.Globalization.CultureInfo culture）
 {
 throw new NotImplementedException（）; 
} 
} 
  

有了这两个类，我们现在可以做休息在Xaml中，首先我们在资源中需要这些类的实例： -

 < UserControl.Resources> 
< local：StaticSurrogate x：Key =Static/> 
< local：FormatConverter x：Key =Formatter/> 
< /UserControl.Resources> 
  

现在我们可以连接 TextBlock -

 < TextBlock Text ={Binding Today，Source = {StaticResource Static}，
 Converter = {StaticResource Formatter}，ConverterParameter ='dd MMM yyy'}/> 
  

请注意，这种方法具有以下优点： -

• 我们不需要向放置TextBlock的UserControl添加代码，也不需要随意转动任何数据上下文。


• 静态资源可以被放置在App.Resources中，这样可以使TextBlock的创建完全独立于不必为UserControl添加任何东西。


• 用于显示日期的格式可以独立修改。


• 访问其他静态属性可以轻松地添加到 StaticSurrogate 类中。

I am coming from Flex where you can do just about anything inside of curly braces. I am trying to get a TextBlock to display today's Date and Time without just coding it in C#. I have tried many different variations of the following with no luck.

TextBlock Text="{Source=Date, Path=Now, StringFormat='dd/MM/yyyy'}"

I know I could probably just set a property MyDate and bind to that but why can't I bind directly to the DateTime.Now property?

解决方案

Binding in Silverlight requires a Source object or a Dependency object. From that source object you can bind to Properties (hence by definition you are binding to instance members) or Dependency Properties.

Since DateTime.Now is a static property you cannot bind to it in Silverlight directly, hence some code is needed. The next best thing is to use code to:-

• ensure as much of what you need can be expressed in XAML
• to do so in an as de-coupled manner as possible.

Hence we can analyse that we need two things.

1. Expose the static members of DateTime as instance properties of some object
2. Have some way to format the DateTime to a desirable output.

To handle the first item I would create a StaticSurrogate class, where I would create instance properties for the static properties that we need access to:-

public class StaticSurrogate
{
    public DateTime Today { get { return DateTime.Today; } }
    public DateTime Now { get { return DateTime.Now; } }
}

Now we need a way to format a Date time. A value converter is the right tool for this job, borrowing heavily from this Tim Heuer Blog :-

public class FormatConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (parameter != null)
        {
            string formatterString = parameter.ToString();

            if (!String.IsNullOrEmpty(formatterString))
            {
                return String.Format(culture, String.Format("{{0:{0}}}", formatterString), value);
            }
        }

        return (value ?? "").ToString();
    }

    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
}

With these two classes in place we can now do the rest in Xaml, first we need instances of these classes in our resources:-

<UserControl.Resources>
    <local:StaticSurrogate x:Key="Static" />
    <local:FormatConverter x:Key="Formatter" />     
</UserControl.Resources>

Now we can wire up the TextBlock :-

<TextBlock Text="{Binding Today, Source={StaticResource Static},
    Converter={StaticResource Formatter}, ConverterParameter='dd MMM yyy'}" />

Note that this approach has the following advantages:-

• we do not need to add code to the UserControl on which the TextBlock is placed, nor do we have to fiddle around with any data context.
• The Static resources could be placed in the App.Resources which would make the creation of the TextBlock entirely independent of having to add anything else to the UserControl.
• The formatting used to display the date can be independently modified.
• Access to additional static properties can easily be added to the StaticSurrogate class.

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