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Is it possible to coerce the UpDown value?
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Joe
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Joe asked on 15 Nov 2019, 04:05 AM

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?

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Dimitar Dinev
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answered on 15 Nov 2019, 02:48 PM

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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Dimitar Dinev
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