C# 如何设置常量十进制值
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How to set a constant decimal value
提问by ldsenow
I'm using C# to set a default value for a decimal value in my config class
我正在使用 C# 为我的配置类中的十进制值设置默认值
public class ConfigSection : ConfigurationSection
{
[ConfigurationProperty("paymentInAdvanceAmount", **DefaultValue = 440m**)]
public decimal PaymentInAdvanceAmount
{
get { return (decimal)base["paymentInAdvanceAmount"]; }
set { base["paymentInAdvanceAmount"] = value; }
}
}
but it won't be compiled and throws an error
但它不会被编译并抛出错误
An attribute argument must be a constant expression, typeof expression
属性参数必须是常量表达式，typeof 表达式
I found a post says: "It's not a bug. "1000M" is merely shorthand for "new Decimal(1000)", which involves a method call, which means it's not considered a constant. Just because the compile lets you pretend it's a constant most of the time, doesn't mean you can all of the time."
我发现一个帖子说：“这不是一个错误。“1000M”只是“new Decimal(1000)”的简写，它涉及一个方法调用，这意味着它不被认为是一个常量。仅仅因为编译让你假装它是一个大部分时间保持不变，并不意味着你可以一直保持。”
Now, how do I workaround it?
现在，我该如何解决它？
回答by Ed S.
Just use 440 and leave out the 'M'. I get no compilation errors, and this program works as expected:
只需使用 440 并省略“M”。我没有遇到编译错误，这个程序按预期工作：
namespace WindowsApplication5
{
public partial class Form1 : Form
{
public Form1( )
{
InitializeComponent( );
AttributeCollection attributes =
TypeDescriptor.GetProperties( mTextBox1 )[ "Foo" ].Attributes;
DefaultValueAttribute myAttribute =
( DefaultValueAttribute ) attributes[ typeof( DefaultValueAttribute ) ];
// prints "440.1"
MessageBox.Show( "The default value is: " + myAttribute.Value.ToString( ) );
}
}
class mTextBox : TextBox
{
private decimal foo;
[System.ComponentModel.DefaultValue( 440.1 )]
public decimal Foo
{
get { return foo; }
set { foo = value; }
}
}
}
回答by ldsenow
I finally found out it I enter "440" instead of 440m or 440. It got compiled and runs well
我终于发现我输入了“440”而不是 440m 或 440。它被编译并且运行良好
回答by ldsenow
You should place 440 inside quotation marks, like this:
您应该将 440 放在引号内，如下所示：
[ConfigurationProperty("paymentInAdvanceAmount", DefaultValue = "440")]
回答by user461707
I found that if you set a default value for a decimal property and specified that value in quotes, it did not work for me with a WinForms control and .NET 3.5.
我发现如果您为小数属性设置默认值并在引号中指定该值，则它不适用于 WinForms 控件和 .NET 3.5。
When ever I right clicked on the property in the designer "Properties" window and selected the "Reset" option I got the message "Object of type 'System.String' cannot be converted to type 'System.Decimal'.
当我右键单击设计器“属性”窗口中的属性并选择“重置”选项时，我收到消息“'System.String'类型的对象无法转换为'System.Decimal'类型。
To get it to work I had to use the same code as tphaneuf suggested i.e.
为了让它工作，我必须使用与 tphaneuf 建议的相同的代码，即
[DefaultValue(typeof(Decimal), "440")]
public decimal TestValue { get; set; }
