WPF中的自定义NumericUpDown ValueChanged事件

Question

Since WPF doesn't contain a NumericUpDown control as known from WinForms , I implemented my own and take care of upper and lower value bounds as well as other validation.

Now, the WinForms NumericUpDown held a ValueChanged event which would be nice to implement it too. My question is: How can I lift the TextChangedEvent of a TextBox to my main application? Delegate s? Or are there any other preferred ways to implement this?

Answer 1

I would personally prefer to use a delegate for this purpose, as I can set my own input parameters for it. I would do something like this:

public delegate void ValueChanged(object oldValue, object newValue);

Using object as the data type would allow you to use different numerical types in the NumericUpDown control, but then you'd have to cast it to the correct type each time... I'd find this a bit of a pain, so if your control would only use one type, int for instance, then you could change your delegate to this:

public delegate void ValueChanged(int oldValue, int newValue);

Then you would need a public property for users of the control to attach handlers:

public ValueChanged OnValueChanged { get; set; }

Used like so:

NumericUpDown.OnValueChanged += NumericUpDown_OnValueChanged;

...

public void NumericUpDown_OnValueChanged(int oldValue, int newValue)
{
    // Do something with the values here
}

Of course, that's no good unless we actually call the delegate from inside the control and let's not forget to check for null in case no handler has been attached:

public int Value
{ 
    get { return theValue; }
    set
    { 
        if (theValue != value)
        {
            int oldValue = theValue;
            theValue = value;
            if (OnValueChanged != null) OnValueChanged(oldValue, theValue);
            NotifyPropertyChanged("Value"); // Notify property change
        }
    }
}