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Nullable<T>.Value 属性

2013/12/13

获取当前的 Nullable<T> 值。

Namespace:  System
程序集:  mscorlib(位于 mscorlib.dll 中)

public T Value { get; }

属性值

类型: T
如果 HasValue 属性为 true,则为当前 Nullable<T> 对象的值。如果 HasValue 属性为 false,则将引发异常。

异常条件
InvalidOperationException

HasValue 属性为 false

下面的代码示例在 Nullable<T> 对象具有已定义值的情况下返回该对象的值;否则返回默认值。


// This code example demonstrates the Nullable<T>.HasValue 
// and Value properties.

using System;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      DateTime? myNow;

      //  Assign the current date and time to myNow then display its value.
      myNow = DateTime.Now;
      Display(outputBlock, myNow, "1) ");

      //  Assign null (Nothing in Visual Basic) to myNow then display its value.
      myNow = null;
      Display(outputBlock, myNow, "2) ");
   }

   // Display the date and time.
   public static void Display(System.Windows.Controls.TextBlock outputBlock, DateTime? displayDateTime, string title)
   {
      // If a value is defined for the displayDatetime argument, display its value; otherwise, 
      // display that no value is defined.
      outputBlock.Text += title;
      if (displayDateTime.HasValue == true)
         outputBlock.Text += String.Format("The date and time is {0:F}.", displayDateTime.Value) + "\n";
      else
         outputBlock.Text += "The date and time is not defined." + "\n";
   }
}

/*
This code example produces the following results:

1) The date and time is Tuesday, April 19, 2005 4:16:06 PM.
2) The date and time is not defined.

*/


Windows Phone OS

受以下版本支持: 8.0, 7.1, 7.0

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