模型binder无法处理double.MAX字符串表示形式返回到double [英] Model binder can't handle double.MAX string representation back to double

问题描述

现在我有一个属性 double Maximum 的ViewModel。在视图方面，它保留在隐藏的输入中，以帮助不显眼的验证。

当发布后备值时，绑定会以静默方式失败。我不得不在这一行上放一个断点：

  if（ModelState.IsValid）
  

并检查哪个 ModelState 属性有错误。然后我发现这个 double Maximum property has a error with the following message：

从System.String类型到
'System.Double'的参数转换失败。查看更多
信息的内部异常。

在视图侧检查 HTML 与 Firebug 我可以看到隐藏的输入有这个值：

  1.79769313486232E + 308 
  

其中正确表示 double.MAX 常量。

我发现这个Scott Hanselman的帖子来自于2005年1月/ 2005年（几乎9年前），处理类似的事情：

为什么你不能Double.Parse（Double.MaxValue.ToString（））或System.OverloadExceptions当使用Double.Parse

我的应用程序配置有问题或从 strin直接转换g 回到 double 不支持？注意：我尝试使用Firebug更改隐藏的输入值，并以Scott的身份在他的帖子中做了说明。 ：我从最后一位数字减去1 ...

  1.79769313486231E + 308 
  

并再次做了回发，只是为了找到这次正确处理的模型binder。

解决方案

我使用 @ Html.HiddenFor 创建隐藏的输入。

在仔细阅读Scott的帖子后，我看到他提到了往返说明符。我还在StackOverflow上找到了一个例子。

R代表往返。从 MSDN ：

只有单和双类型才支持此格式。往返说明符保证转换为
字符串的数值将被解析为相同的数值。

所以我这样做：

  @ Html.HiddenFor（m => m.Maximum，
 new {Value = Model.Maximum.ToString（R）}）
  

现在这给了我一个 double.MAX 字符串表示，可以回滚到控制器端的 double ：

  1.7976931348623157E + 308 
  

尼斯...问题解决了。

希望它帮助任何可能面临同样问题的人。

---

这是多么有趣！

  1.79769313486232E + 308 // double。 MAX 
 1.7976931348623157E + 308 // double.MAX.ToString（R）
  

值得一提的是，所有这一切也适用于 double.MIN 。

Right now I have a ViewModel with a property double Maximum. On the view side it's kept in a hidden input to help with unobtrusive validation.

When post backing the values, the binding silently fails. I had to put a breakpoint on this line:

if(ModelState.IsValid)

and check which ModelState property had an error. Then I found that this double Maximum property had an error with the following message:

The parameter conversion from type 'System.String' to type 'System.Double' failed. See the inner exception for more information.

On the view side inspecting the HTML with Firebug I can see that the hidden input has this value:

1.79769313486232E+308

which correctly represents double.MAX constant.

I found this Scott Hanselman post from Jan/2005 (almost 9 years ago) which deals with something similar:

Why you can't Double.Parse(Double.MaxValue.ToString()) or System.OverloadExceptions when using Double.Parse

Is there something wrong with my app config or this direct conversion from string back to double is not supported? I think it should handle it without errors.

Note: I tried changing the hidden input value with Firebug and did as Scott mentions on his post: I subtracted 1 from the last digit...

1.79769313486231E+308

and did a postback again just to find the model binder handled it correctly this time.

解决方案

I'm using @Html.HiddenFor to create the hidden input.

After carefully reading Scott's post I saw that he mentions the round-trip specifier. I also found an example here on StackOverflow.

The R stands for "round-trip". From MSDN:

This format is supported only for the Single and Double types. The round-trip specifier guarantees that a numeric value converted to a string will be parsed back into the same numeric value.

So I did this:

@Html.HiddenFor(m => m.Maximum,
                new { Value = Model.Maximum.ToString("R") })

Now this gives me a double.MAX string representation that can be round-tripped back to a double on the controller side:

1.7976931348623157E+308

Nice... problem solved.

Hope it helps anyone that might face this same problem in the future.

---

How interesting this is?!

1.79769313486232E+308   // double.MAX
1.7976931348623157E+308 // double.MAX.ToString("R")

It's worth mentioning that all this is also applicable to double.MIN.

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