覆盖十进制ToString（）方法

Question

I have a decimal datatype with a precision of (18, 8) in my database and even if its value is simply 14.765 it will still get displayed as 14.76500000 when I use Response.Write to return its value into a webpage.

Is it possible to override its default ToString method to return the number in the format #,###,##0.######## so that it only displays relevant decimal places?

UPDATE

I'm assuming that when one outputs number on a page like <%= item.price %> (where item.price is a number) that the number's ToString method is being called?

I'm trying to avoid having to change every instance where the value is displayed by defaulting the ToString() format somehow.

Answer 1

您不想重写ToString() ，您想调用ToString()并指定IFormatProvider或格式化String

Answer 2

You can't override ToString for decimal type since it's a struct .

But you can use extension methods to do so:

public static class DecimalExtensions
{
      public static string ToString(this decimal some, bool compactFormat)
      {
            if(compactFormat) 
            {
                return some.ToString("#,###,##0.########");
            }
            else
            {
                return some.ToString();
            }
      }
}

So now you can do this:

string compactedDecimalText = 16.38393m.ToString(true);

Answer 3

I ran into the same problem as you. People wanted decimals to be formatted in crazy custom ways throughout the application.

My first idea was to create a wrapper around Decimal and override the ToString() method.

Although you cannot inherit from Decimal, you can create a type that implicitly casts to and from a Decimal.

This creates a facade in front of Decimal, and gives you a place to write custom formatting logic.

Below is my possible solution, let me know if this works or if this is a horrible idea.

public struct Recimal
{

    private decimal _val;
    public Recimal(decimal d) { _val = d; }

    public static implicit operator Recimal(decimal d)
    {
        return new Recimal(d);
    }

    public static implicit operator Decimal(Recimal d)
    {
        return d._val;
    }

    public override string ToString()
    {
        //if negative, show the minus sign to the right of the number
        if (_val < 0)
            return String.Format("{0:0.00;0.00-;}", _val);

        return _val.ToString();
    }

}

It works just like a Decimal:

        Decimal d = 5;
        Recimal r = -10M;
        Recimal result = r + d;

        //result: 5.00-
        textBox1.Text = result.ToString();

Answer 4

Why not use string.Format() directly on double ?

Here are some references for the formatting options:

• Formatting Double
• MSDN Numeric Format