如何将使用Rx Observable.FromEventPattern编写的用于事件处理程序的函数转换为纯.net事件处理程序（不带Rx）

Question

I have a code snippet that someone has written using Rx in C# that uses Observable.FromEventPattern for event handling.

Here's the existing code that I have which uses Rx

private void RegisterToDigitFocusEvents(int index, TextBox digit)
{
    Observable.FromEventPattern<RoutedEventHandler, RoutedEventArgs>(
        h => digit.GotFocus += h,
        h => digit.GotFocus -= h)
        .SubscribeToElement(digit,
            _ => this.ResetDigit(digit, index),
            error => this.Log().Error("Observing digit GotFocus", error),
            () =>
            {
                /* Do nothing on complete */
            });
}

I am not allowed to use Rx in my project. I looked up the documentation for FromEventPattern, I was unable to clearly understand what is the pure .Net equivalent of writing the same code without Rx

Here's my attempted conversion which as you might know didn't work quite as expected

//Global index so that it can be used across functions
int index1;

private void RegisterToDigitFocusEvents(int index, TextBox digit)
{
    digit.GotFocus += digit_GotFocus;
    index1 = index;
}

void digit_GotFocus(object sender, RoutedEventArgs e)
{
    this.ResetDigit(sender as TextBox, index1);
}

As you notice I haven't written code to unregister the event handler. I am not sure where to put the logic.

I am a beginner to Rx. Just to be clear - I do not want re implement the whole observable pattern that Rx provides me, I just want to write a function equivalent of the first snippet without using Rx, pure .Net events. Any help to write the first code snippet in this post without Rx would be highly appreciated.

Answer 1

It seems to me that this is the pure equivalent:

    private void RegisterToDigitFocusEvents(int index, TextBox digit)
    {
        RoutedEventHandler gotFocusHandler = (s, e) =>
        {
            try
            {
                this.ResetDigit(digit, index)
            }
            catch (Exception error)
            {
                this.Log().Error("Observing digit GotFocus", error);
            }
        };

        digit.GotFocus += gotFocusHandler;
    }

You really should extend this code to handle the detaching of the handler when your form closes, but the above should be the basics required.

Please let me know if I've misunderstood the question.