How to set a constant decimal value

Question

Hi guys

I'm using C# to set a default value for a decimal value in my config class

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

An attribute argument must be a constant expression, typeof expression

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."

Now, how do I workaround it?

Answer 1

Just use 440 and leave out the 'M'. I get no compilation errors, and this program works as expected:

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; }
        }
    }
}

Answer 2

My Code as below

public class ConfigSection : ConfigurationSection {

    [ConfigurationProperty("paymentInAdvanceAmount", **DefaultValue = 440m**)]
    public decimal PaymentInAdvanceAmount
    {
        get { return (decimal)base["paymentInAdvanceAmount"]; }
        set { base["paymentInAdvanceAmount"] = value; }
    }

}

In my web app

protected void Page_Load(object sender, EventArgs e) { Response.Write(ConfigSection.PaymentInAdvanceAmount); }

with 440m it got compiled not successfully, with 440 or 440.00 it got compiled but another error will get thrown The default value for the property 'paymentInAdvanceAmount' has different type than the one of the property itself

Answer 3

I finally found out it I enter "440" instead of 440m or 440. It got compiled and runs well

Answer 4

You should place 440 inside quotation marks, like this:

[ConfigurationProperty("paymentInAdvanceAmount", DefaultValue = "440")]

Answer 5

yes. have double quotation marks and it works.

Answer 6

[DefaultValue(typeof(Decimal), "440")]

public decimal TestValue { get; set; }

Answer 7

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.

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'.

To get it to work I had to use the same code as tphaneuf suggested i.e.

[DefaultValue(typeof(Decimal), "440")]
public decimal TestValue { get; set; }