Is it possible to coerce the UpDown value?

[Joe]

I'm wondering if you can suggest an approach to achieve an effect I want (which I describe below).  I don't think so but I thought I would check.

I'm using a NumericUpDown to show length values of type double.    I want to be able to make the Up/Down buttons change the displayed value to an even multiples of a a whole number, regardless of the starting value or the direction (up vs down)  of the button they hit.  Is there a way to do this?

For example, suppose the initial value is 1.23.   

If the user hits the "Up" button, I want the value to change from 1.23 to 2.00. But the next time he/she hits it I want it to change from 2.00 to 3.00
But if the user hits the "Down" button, I want the value to change from 1.23 to 1.00.  The next time, I want it to change from 1.00 to 0.00

If there were separate "SmallChange" properties for the up and down directions, this would be easy.   I could bind them and do the math whenever the value changes.  But I only have the one "SmallChange" property.

If there were some way for me to insert a "CoerceValue" callback into the "Value" property, I could do that.  But I don't believe that is possible.  If it is, please tell me how

Is there any way to achieve this?

[Dimitar Dinev]

Hi Joe,

Thank you for the description.

You can achieve this behavior by implementing custom logic in the setter of the property you have bound to the Value property. Please, take a look at the following code snippet which checks if the value is a whole number:

privatedouble boxValue = 1.23;

publicdouble BoxValue
{
    get { return boxValue; }
    set
    {
        var isIncreasing = value > this.boxValue;

        if (isIncreasing)
        {
            boxValue = (int)value;
        }
        else
        {
            if (!(this.boxValue == Math.Truncate(boxValue)))
            {
                this.boxValue = Math.Truncate(boxValue);
            }
            else
            {
                this.boxValue = boxValue - 1;
            }
        }
        OnPropertyChanged("BoxValue");
    }
}

Attached, you can find a sample project demonstrating this approach. Please, review it and let me know if it delivered the desired result.

Regards,
Dimitar Dinev
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