C# NumericUpDown.OnValueChanged, how it was changed?

Question

I would like to ask how to make custom EventArgs for existing event handler.

Lets say, that I have NumericUpDown numericUpDown control and I want handler for its OnValueChanged event. Double clicking to ValueChanged in visual studio makes snippet like this

private void numericUpDown_ValueChanged(object sender, EventArgs e)
{

}

However, I'd like to know how it was changed (like +5, -4.7), but plain EventArgs does not have this information. Maybe Decimal change = Value - Decimal.Parse(Text) would do the trick (because of delayed text change), but that's ugly way and may not work every single time.

I guess I should make my own EventArgs like this

class ValueChangedEventArgs : EventArgs
{
    public Decimal Change { get; set; }
}

and then somehow override NumericUpDown.OnValueChanged event to generate my EventArgs with proper information.

Could you just store the previous value of the control and then compare it to the current value in the event handler? — APerson, Sep 19 '14 at 16:17
@APerson If I had more controls of this type using same event handler, I would have to store all possible previous values during whole runtime. — Zereges, Sep 19 '14 at 16:22
There is no built-in storage of previous content. If you need to track that to calculate value changes, you'll need to store it yourself. — Ken White, Sep 19 '14 at 16:24
@Zereges Then make a `Dictionary` mapping `NumericUpDown`s to the values they formerly held. — APerson, Sep 19 '14 at 16:24

score 2 · Accepted Answer · answered Sep 19 '14 at 16:23

2

It may be much easier to just tag the last value.

    private void numericUpDown1_ValueChanged(object sender, EventArgs e) {
        NumericUpDown o = (NumericUpDown)sender;
        int thisValue = (int) o.Value;
        int lastValue = (o.Tag == null) ? 0 : (int) o.Tag;
        o.Tag = thisValue;
        MessageBox.Show("delta = " + (thisValue - lastValue));
    }

answered Sep 19 '14 at 16:23

zam664

757
1
7
18

Well, I didn't think about using tag for this. This could do the trick, I'll probably use it. However, if I wanted to use custom event args, how would I do that? – Zereges Sep 19 '14 at 16:26
1

Just small warning for anyone trying to do the same. `(int) o.Tag` throws `InvalidCastException`, so use rather `int.Parse(o.Tag.ToString())` or `Convert.ToInt32(o.Tag)` – Zereges Sep 19 '14 at 16:43

score 0 · Answer 2 · answered Sep 19 '14 at 16:24

You would have to create your own numeric up down control that extends the .net version, define a delegate type for your event and then hide the base controls event property.

Delegate:

public delegate void MyOnValueChangedEvent(object sender, ValueChangedEventArgs args);

Event Args Class:

class ValueChangedEventArgs : EventArgs
{
    public Decimal Change { get; set; }
}

New NumericUpDown class, hide the inherited event with 'new':

public class MyNumericUpDown : NumericUpDown
{
    public new event MyOnValueChangedEvent OnValueChanged;
}

Look here for instructions on how to raise your custom event, and here for additional information on event handling.

C# NumericUpDown.OnValueChanged, how it was changed?

2 Answers2

Linked