如何在NumericUpDown旋转框中显示不同的单位？

Question

I'm trying to create a control that will allow users to enter a length in a unit of their choice. For the sake of brevity, I'm limiting my code below to centimeters and inches, but in actuality their are more units to choose from than just those two (2).

I thought I could just affect the display of a spinbox with overrides of UpdateEditText() and ValidateEditText() . This is what I came up with:

public enum UnitSystem { Metric, Imperial };

public class UnitNumberUpDown : NumericUpDown
{
    public UnitNumberUpDown() { }

    private void IncrementAndRound(decimal conversion, int denominator)
    {
        this.Increment = conversion / denominator;
        this.Maximum = conversion * Math.Round(MaximumPointSize * denominator / conversion) / denominator;
        this.Value = conversion * Math.Round(this.Value * denominator / conversion) / denominator;
    }

    public decimal MaximumPointSize { get; set; }

    private UnitSystem units;
    public UnitSystem Units
    {
        get { return units; }
        set { if (value != Units) {
                units = value;
                switch (Units)
                {
                    case UnitSystem.Metric:
                        IncrementAndRound(POINTS_PER_CM, 80);
                        break;
                    case UnitSystem.Imperial:
                        IncrementAndRound(POINTS_PER_INCH, 64);
                        break;
                }
            }
        }
    }

    private const decimal POINTS_PER_CM = 28.3464567m;
    private const decimal POINTS_PER_INCH = 72m;

    protected override void UpdateEditText()
    {
        switch (Units)
        {
            case UnitSystem.Metric:
                this.Text = (this.Value / POINTS_PER_CM).ToString("0.00");
                break;
            case UnitSystem.Imperial:
                this.Text = (this.Value / POINTS_PER_INCH).ToString("0.00");
                break;
        }
    }

    protected override void ValidateEditText()
    {
        try {
            decimal value = decimal.Parse(this.Text.Trim());
            switch (Units)
            {
                case UnitSystem.Metric:
                    this.Value = value * POINTS_PER_CM;
                    break;
                case UnitSystem.Imperial:
                    this.Value = value * POINTS_PER_INCH;
                    break;
            } 
        } catch {
            base.ValidateEditText();
        }
    }
}

The above doesn't work all the time. Sometimes, ValidateEditText() is invoked in the wrong order relative to the Units property changing and the switch statement causes an incorrect conversion.

How would I either fix the code implementation or my design?

Answer 1

I'd select numbers in NumericUpDown , while units in ComboBox next to it. Its the most obvious for the customer thing to use.

MS Word numeric up-down with units is working differently, than your solution. In there you have only one unit (lets say cm ). You can enter text with any units (to example, mm ), but it get internally converted to said unit ( cm ). Text is not updated until you press Up Down or close the window (next time it is opened, you will see value in cm ).

I think you have to check for TextChanged (not ValidateEditText , but keep it overriden and doing nothing), just threat it differently when you are setting text in UpdateEditText . Another thing is dynamic increment/decrement. It may not work well for the user (to example, user is expecting to have value incremented by 0.1 disregards of units).

Also, check this .