CODEWITHSUNDEEP
c#.netwinforms
Boris
Boris

Reputation: 8931

Creating a hexadecimal NumericUpDown control

I have created a hexadecimal NumericUpDown control by sub-classing the basic NumericUpDown and adding the following method:

protected override void UpdateEditText()
{
  this.Text = "0x" + ((int) Value).ToString("X2");
}

This works pretty well. The control now shows values in the format:

0x3F

which is exactly what I was after.

But one thing bothers me: every time the Text-property is assigned, a System.FormatException is thrown. This doesn't seem to affect the control's functionality, but still I think it's ugly.

This is the top of the callstack:

MyAssembly.dll!HexNumericUpDown.UpdateEditText() Line 31 C# System.Windows.Forms.dll!System.Windows.Forms.NumericUpDown.ValidateEditText() Unknown System.Windows.Forms.dll!System.Windows.Forms.UpDownBase.Text.set(string value) Unknown

Can I just ignore this exception? Or is there a clean way to get rid of this?

Upvotes: 8

Views: 2076

Answers (3)

Hans Passant
Hans Passant

Reputation: 941455

You need to override the ValidateEditText() method so you can properly handle the (optional) "0x" prefix. And override UpdateEditText() to prefix "0x". Add a new class to your project and paste the code shown below. Compile. Drop the new control from the top of the toolbox onto your form:

using System;
using System.Windows.Forms;

class HexUpDown : NumericUpDown {
    public HexUpDown() {
        this.Hexadecimal = true;
    }

    protected override void ValidateEditText() {
        try {
            var txt = this.Text;
            if (!string.IsNullOrEmpty(txt)) {
                if (txt.StartsWith("0x")) txt = txt.Substring(2);
                var value = Convert.ToDecimal(Convert.ToInt32(txt, 16));
                value = Math.Max(value, this.Minimum);
                value = Math.Min(value, this.Maximum);
                this.Value = value;
            }
        }
        catch { }
        base.UserEdit = false;
        UpdateEditText();
    }

    protected override void UpdateEditText() {
        int value = Convert.ToInt32(this.Value);
        this.Text = "0x" + value.ToString("X4");
    }
}

Fwiw, the quirky try/catch-em-all comes straight from the .NET version. I kept it to make the control behave the same way. Tweak the ToString() argument the way you want it.

Upvotes: 7

israel altar
israel altar

Reputation: 1794

There is a Difference between casting and ConvertTo:

(int)obj - this is an explicit cast of obj to the type int, you are telling the compiler that obj is an int. If obj is not a int type, you will get a cast exception. But it is not REALLY an int. and the X2 format needs real ints.

Convert.ToInt32(obj) - This is an explicit call to the Convert class to return a int representation of obj.

Because of that you need to use Convert.ToInt32(Value)

BUT in MSDN it says:

1)This API (numericUpDown.Text) supports the .NET Framework infrastructure and is not intended to be used directly from your code.

2)The Text has no affect on the appearance of the NumericUpDown control; therefore, it is hidden in the designer and from IntelliSense.

Upvotes: 0

Hans Kesting
Hans Kesting

Reputation: 39284

I guess you also need to override the ParseEditText ValidateEditText method, to accept the hex value and set the Value property to the correct int value.

Upvotes: 0

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