Please help me to figure out a purpose of this code.

Pew_new

This is in a Class called ST:

public Class ST
{
private readonly System.Timers.Timer _timer;
private DateTime _lastScanTime;

public ST()
{

        \_timer = new System.Timers.Timer();
        \_timer.Interval = 250;
        \_timer.Start();
        \_timer.Elapsed += OnTimerElapsed;
    }



     public TimeSpan ScanTime { get; private set; }

      private void OnTimerElapsed(object sender, ElapsedEventArgs e)
    {
        try
        {
            \_timer.Stop();
            ScanTime = DateTime.Now - \_lastScanTime;
            
            OnValuesRefreshed();
        }
        finally
        {
            \_timer.Start();
        }
        \_lastScanTime = DateTime.Now;
    }
    
    private void OnValuesRefreshed()
    {
        ValuesRefreshed?.Invoke(this, new EventArgs());
    }

}

Then a value of Scantime is being transferred via MVVM pattern (ViewModel) to UI. The major question is what do we really have valuable when we do a substraction as follows: ScanTime = DateTime.Now - _lastScanTime? This point I can't figure out. Thanks in advance!

Mycroft Holmes

This code would be called in a loop structure. First time it is called _LastScanTime is populated and the ScanTime is irrelevant. All subsequent calls update the ScanTime using subtraction and the _LastScanTime with the current time. I suggest you get a book (or many books) and work through the examples if this simple logic baffles you.

Never underestimate the power of human stupidity RAH

Pew_new

@__Holmes__, my dear, oddly enough, I knew a structure of this code, like nobody's business. I asked a bit a different stuff. Let me repeat that: I wish I knew what we really have useful by substraction as follows: ScanTime = DateTime.Now - _lastScanTime?? When the code is running I have a quickly alterating value 250-270 ms. P.S. Next time, before replying, just try to read posts more carefully. As concerned books, please do me a favour, show me a book where is written for what it is being done by mentioned substraction. I'll be waiting for such useful book. Pew

Mycroft Holmes

So you have a ScanTime of 250-270ms. It is generated by subtracting the current time (DateTime.Now) from the _LastScanTime which was populated by the last loop. It represents the number of milliseconds the system takes to complete the processing loop from the VM. PS It is still a very straight forward piece of code which is staggeringly simple. Try adding

Thread.Sleep(100)

after your subtraction line and see what happens.

Never underestimate the power of human stupidity RAH

Lost User

Pew_new wrote:

The major question is what do we really have valuable when we do a substraction as follows: ScanTime = DateTime.Now - _lastScanTime?

I cannot see anything 'valuable' in this. It merely gives you the actual elapsed time between the timer start and the first tick. Since your timer interval is set at 250 (milliseconds) it should be somewhere around that value. The question really is what this code is being used for?

Pew_new

Holmes> It represents the number of milliseconds the system takes to complete the processing loop from the VM. I was waiting for this sentence.:thumbsup: For what this stands for? I mean, e.g. a label with mentioned milliseconds inside, on UI screen. Just show to UI user that app is alive?

Pew_new

Richard MacCutchan> The question really is what this code is being used for? I would ask you this way. :) My guess is it provides an UI user some kind of "Warning". Something like "Your PC's processor is so busy that the ScanTime went out of allowed time range." Of course in case when value is out of tolerance "window". A value is out of tolerancee "window" - text of value is highlighted with red.

Lost User

So why exactly are you asking here? We have no information on the context that this code runs inside, or what the application is trying to do.

Pew_new

Some info I gave in the first post: Timer -> Timer procedure and calculation -> MVVM pattern -> UI. As said Mr.Holmes. It's very simple code.:thumbsup:

Lost User

Which means absolutely nothing. I still do not understand exactly what you are asking.

Pew_new

It may close this topic. I've got comrehensive answer from Mr.Holmes. If you're interested in. This is answer: It represents the number of milliseconds the system takes to complete the processing loop from the VM.

Lost User

No, it is just the number of milliseconds between the timer starting, and the Elapsed event being fired. This will occur after approximately 250 milliseconds as declared by the timer intialisation values.

Pete OHanlon

There appear to be a couple of structural issues with this code. The first thing is, you haven't shown us the complete class. Secondly, you update _lastScanTime to a different DateTime.Now than when you update ScanTime - in a multi-threaded application, this could be a potentially significant difference because of your ValuesRefreshed. To be honest, I don't know why you don't make ScanTime raise INotifyPropertyChanged.PropertyChanged and avoid other events; you can bind directly to that value. Also, I would use a StopWatch instead of DateTime.Now if I were you.

This space for rent

Mycroft Holmes

Richard MacCutchan wrote:

This will occur after approximately 250 milliseconds as declared by the timer intialisation values.

Ah crap I completely missed that, even after rereading the dammed code.

Never underestimate the power of human stupidity RAH

Lost User

We've all done that from time to time. Although, I was actually worried that I was missing something that you had noticed.