Re: Event for checking if a delegate/anonymous method result changed - C# Discussion Boards

Re: Event for checking if a delegate/anonymous method result changed

14-Dec-10 3:40

Hi all,
I was wondering if there is a smooth way to accomplish the following:

Lets say I have a class that accepts delegates (or anonymous methods) that return strings.
Those refs are then stored.

I want to create an eventhandler that is fired when a result of such a delegate changes
(just like the TextChanged event of TextBox but maybe named: DelegateResultChanged)

I came up with a background thread that periodically calls the delegate and compares the result with the original result,
but that seems a little too much for archiving the desired result.

Any ideas on how this can be done "the right way"?

Any ideas are kindly appreciated
best regards
Andy

Abhinav S14-Dec-10 5:14

Abhinav S

14-Dec-10 5:14

If you are using binding, you might want to consider looking at INotifyPropertyChanged as shown here[^].

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Re: Event for checking if a delegate/anonymous method result changed

hoernchenmeister14-Dec-10 5:45

Re: Event for checking if a delegate/anonymous method result changed

14-Dec-10 5:45

Unfortunately I am unable to use binding for this one.
I deal with Control objects that do not provide the PropertyChanged event.

Anyway, thanks a lot for your contribution!!

Ian Shlasko14-Dec-10 5:25

Ian Shlasko

14-Dec-10 5:25

Well, the result changes when one or more of the inputs change, so what you really need to watch for is a change to the inputs. If this is on an object that implements change notification, you could pass that through and only check for a new result if the object reports a change.

But as for a changed event on the function itself... To my knowledge, no such thing exists. That function isn't going to re-run every time the inputs change, so the program doesn't even know what the new result is until you ask for it.

Off the top of my head, another alternative...

Instead of passing a function, wrap that up in a lightweight class:

public class FunctionWatcher
{
  public FunctionWatcher(INotifyPropertyChanged caller, Delegate function)
  {
    // ...
  }

  private Delegate Callback;
  public object Result { get; private set; }
  public event EventHandler ResultChanged;

  private void CallerPropertyChanged(...)
  {
    // invoke the callback, update Result, call ResultChanged if appropriate
  }
}

Again, this relies on having some object providing change notification... Otherwise your current solution might be the only one.

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Re: Event for checking if a delegate/anonymous method result changed

hoernchenmeister14-Dec-10 5:43

Re: Event for checking if a delegate/anonymous method result changed

14-Dec-10 5:43

That sounds pretty good.

The reason for dealing with this is to have some kind of watcher that is able to be fed with Control objects in order to tell if
something has changed in one control or a group of controls and saving is required.

So I am dealing with List<Control> where Control does not provide the PropertyChanged interface.

I already implemented TextChanged for those Control objects to raise the "SomethingHasChangedEvent".

So far everything works fine.

The delegate option is an addon for cases where something else has to be watched instead of a Control object.
Let's assume a function that checks some DataGrid fields or whatever, cases where I do not want to register a lot of Controls to get a TextChanged handler attached.

After thinking about this for a while I recognized that asking the watcher if it is "dirty" and going through the delegate list for checking this might be enough.
On the other hand, why not providing this event, it might become useful later... yeah, and I like events too Wink | ;)

The timer-idea just does not feel well... I have no idea how many work these delegates actually perform, so performance might become an issue later.

Ian Shlasko14-Dec-10 6:07

Ian Shlasko

14-Dec-10 6:07

Hmm... Well, if you can get them all to raise some sort of change event, then you can just subclass a wrapper for each type... One to watch a control for TextChanged, one to watch an object implementing INotifyPropertyChanged, etc etc. They could all, in turn, raise the same change event after checking the result.

Proud to have finally moved to the A-Ark. Which one are you in?
Author of the Guardians Saga (Sci-Fi/Fantasy novels)

Re: Event for checking if a delegate/anonymous method result changed

hoernchenmeister14-Dec-10 6:33

Re: Event for checking if a delegate/anonymous method result changed

14-Dec-10 6:33

Good point Ian, I am just afraid that I am in a situation where I need to provide a fast and flexible solution... that's why I came up with the delegate stuff.
The people who wan't to use it can provide their own mechanism for resolving the original-value and the changed-value...
Just without an event...
I am really not sure if this event would be needed... maybe if some buttons will be disabled if changes have occured... but that's pretty much all I can think about.
I am not sure if I can implement INotifyPropertyChanged (I am used to work with this buddy in WPF - right now it's a WinForm app) on all circumstances...

Imagine a third party control that does not have a Text property or a TextChanged event.
Whatever this control is huge and does not implement INotifyPropertyChanged.
Right now I can pass a delegate to the watcher (it has AddControl(Control control) and AddDelegate(MyDelegate del) methods to add whatever is needed) and the one who uses the watcher can take care about whatever he thinks might be suitable to figure out if changes occured or not.

At that point I am unable to continue without subclassing something in order to bring the INotifyPropertyChanged into play.
I do not wan't the guyzos to change their objects or whatever... they should be able to implement it easily and without too much changes... on the other hand it is quite likely that the watcher will be heavily reused...

...where to go Wink | ;)

What do you think?

Ian Shlasko14-Dec-10 7:30

Ian Shlasko

14-Dec-10 7:30

Well, if the control doesn't raise any useful events, your options are limited, and the timer solution is about all there is (Just make sure it's sleeping between checks, not calling continuously).

Maybe you could hide the complexity with private classes... I'm still in favor of the wrappers to merge all the different possibilities into a single event type... When you pass in the control, it'll check for a few common types (For a TextBox, it would look for TextChanged. For a checkbox, CheckedChanged. If it's an INotifyPropertyChanged, PropertyChanged). Depending on the type of control passed, it creates a different wrapper that hooks the necessary event and supplies a simple Changed event. If it can't find an event to hook, it falls back to the timer method...

public void MonitorObject(object obj, Delegate valueToMonitor) 
{
  if (obj is TextBox)
     Add(new TextChangedWatcher(obj as TextBox, valueToMonitor));
  else if ...
  else
     Add(new DefaultObjectWatcher(obj, valueToMonitor));
}

private class ObjectWatcher
{
  public event EventHandler Changed;
  private Delegate ResultCallback { get; set; }
  private object PreviousValue { get; set; }
  
  protected void OnCheckValue()
  {
    object newValue = ResultCallback.Invoke();
    if (!object.Equals(PreviousValue, newValue))
    {
      PreviousValue = newValue;
      if (Changed != null) Changed(this, EventArgs.Empty);
    }
  }
}
private class TextChangedWatcher : ObjectWatcher
{
  public TextChangedWatcher(TextBox ctl) 
  { 
    // hook TextChanged...
  }
}
private class CheckedChangedWatcher : ObjectWatcher
{
  // hook CheckedChanged
}
private class NotifyObjectWatcher : ObjectWatcher
{
  // hook PropertyChanged
}
private class DefaultObjectWatcher : ObjectWatcher
{
  // Create a timer
}

Anyway... The idea would be to hook events when possible, and only fall back to the timer when there are no known events to hook.

Proud to have finally moved to the A-Ark. Which one are you in?
Author of the Guardians Saga (Sci-Fi/Fantasy novels)

Re: Event for checking if a delegate/anonymous method result changed

hoernchenmeister14-Dec-10 20:38

14-Dec-10 20:38

Yes, you are right Ian.
I guess I'll go for the wrapper (I like wrappers anyway).
Maybe I'll replace the timer-part at a later time, but for now it'll suit my needs Wink | ;)

Thank you Ian for your input, I really appreciate that,
best regards
Andy

Dynamic Polymorphism

Baji Jabbar13-Dec-10 23:31

Baji Jabbar

13-Dec-10 23:31

Why is dynamic polymorphism so called? Want to know why not how it is achieved !

Hiren solanki13-Dec-10 23:48

13-Dec-10 23:48

Take a Look[^], Same holds true for C#.

Regards,
Hiren.
Microsoft Dynamics CRM

My Recent Article: - Way to know which control have raised PostBack[^]

Richard MacCutchan13-Dec-10 23:49

Richard MacCutchan

13-Dec-10 23:49

Here[^] are some reasons.

Just say 'NO' to evaluated arguments for diadic functions! Ash

Hiren solanki13-Dec-10 23:57

13-Dec-10 23:57

Oh!! Thats the bunch from which I selected one. Big Grin | :-D

Regards,
Hiren.
Microsoft Dynamics CRM

My Recent Article: - Way to know which control have raised PostBack[^]

Baji Jabbar14-Dec-10 0:00

Baji Jabbar

14-Dec-10 0:00

Most of the link gives how to achieve dynamic polymorphism. I dint get an accurate answer

Pete O'Hanlon14-Dec-10 0:43

Pete O'Hanlon

14-Dec-10 0:43

There's a fairly reasonable definition of dynamic polymorphism here[^].

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adding new data over ProcessLayer

Richard MacCutchan14-Dec-10 1:02

Richard MacCutchan

14-Dec-10 1:02

maB_J wrote:
I dint get an accurate answer

What do you mean by accurate? Did you read the first link in the list I sent you? It gives a full definition of Dynamic Polymorphism; you could also go to Bjarne Stroustrup's web site and read everything he has to say about it.

Just say 'NO' to evaluated arguments for diadic functions! Ash

Erdinc2713-Dec-10 22:12

Erdinc27

13-Dec-10 22:12

hey guys..i try to add datas by stored procedure with 15 parameters..it works well..the problem is in my ProcessLayer..i have Firmalar class like below.

public class Firmalar
{
    public string firma_adi { get; set; }
    public string yetkili1 { get; set; }
    public string gsm1 { get; set; }
    public string email1 { get; set; }
    public string yetkili2 { get; set; }
    public string gsm2 { get; set; }
    public string email2 { get; set; }
    public string yetkili3 { get; set; }
    public string gsm3 { get; set; }
    public string email3 { get; set; }
    public string telefon1 { get; set; }
    public string telefon2 { get; set; }
    public string telefon3 { get; set; }
    public string telefon4 { get; set; }
    public string telefon5 { get; set; }
}

and i try to add data in my processLayer like that

public void InsertFirm(Firmalar fir)
       {
           try
           {
               fir = new Firmalar();
               cmmd = d.InsertData();
               cmmd.Parameters.AddWithValue("@firmanin_adi", System.Data.SqlDbType.NVarChar).Value = fir.firma_adi;
               cmmd.Parameters.AddWithValue("@yetkili1", System.Data.SqlDbType.NVarChar).Value = fir.yetkili1;
               cmmd.Parameters.AddWithValue("@gsm_num1", System.Data.SqlDbType.NVarChar).Value = fir.gsm1;
               cmmd.Parameters.AddWithValue("@e_mail1", System.Data.SqlDbType.NVarChar).Value = fir.email1;
               cmmd.Parameters.AddWithValue("@yetkili2", System.Data.SqlDbType.NVarChar).Value = fir.yetkili2;
               cmmd.Parameters.AddWithValue("@gsm_num2", System.Data.SqlDbType.NVarChar).Value = fir.gsm2;
               cmmd.Parameters.AddWithValue("@e_mail2", System.Data.SqlDbType.NVarChar).Value = fir.email2;
               cmmd.Parameters.AddWithValue("@yetkili3", System.Data.SqlDbType.NVarChar).Value = fir.yetkili3;
               cmmd.Parameters.AddWithValue("@gsm_num3", System.Data.SqlDbType.NVarChar).Value = fir.gsm3;
               cmmd.Parameters.AddWithValue("@e_mail3", System.Data.SqlDbType.NVarChar).Value = fir.email3;
               cmmd.Parameters.AddWithValue("@tlfn1", System.Data.SqlDbType.NVarChar).Value = fir.telefon1;
               cmmd.Parameters.AddWithValue("@tlfn2", System.Data.SqlDbType.NVarChar).Value = fir.telefon2;
               cmmd.Parameters.AddWithValue("@tlfn3", System.Data.SqlDbType.NVarChar).Value = fir.telefon3;
               cmmd.Parameters.AddWithValue("@tlfn4", System.Data.SqlDbType.NVarChar).Value = fir.telefon4;
               cmmd.Parameters.AddWithValue("@tlfn5", System.Data.SqlDbType.NVarChar).Value = fir.telefon5;
               cmmd.ExecuteNonQuery();
             }

and inside of my form's code i try to send parameters...

  private void  btnEkle_Click(object sender, EventArgs e)
  {
      try
      {
          if (txtFirma_adi.Text.Length != 0)
          {
              firma = new Firmalar();
              h.InsertFirm(firma);
              firma.firma_adi = txtFirma_adi.Text;
              firma.yetkili1 = txtYetkili_adi.Text;
              firma.gsm1 = txtGsm.Text;
              firma.email1 = txtEmail.Text;
              firma.yetkili2 = txtYetkili2.Text;
              firma.gsm2 = txtGsm2.Text;
              firma.email2 = txtEmail2.Text;
              firma.yetkili3 = txtTetkili3.Text;
              firma.email3 = txtEmail3.Text;
              firma.gsm3 = txtGsm3.Text;
              firma.telefon1 = msktlf1.Text;
              firma.telefon2 = mskTlf2.Text;
              firma.telefon3 = mskTlf3.Text;
              firma.telefon4 = msktlf4.Text;
              firma.telefon5 = mskTlf5.Text;
          }
    }
}

but the values dont go to my stored procedure..and it gives error sp_AddDatas expects parameter @firmanin_adi...so how i can send the values to my stored procedure..

vemedya.com

Hiren solanki13-Dec-10 23:17

13-Dec-10 23:17

erdinc27 wrote:
fir = new Firmalar();

Inside method InsertFirm(Firmalar fir) why are you again intializing Object? Use the received object itself.

Regards,
Hiren.
Microsoft Dynamics CRM

My Recent Article: - Way to know which control have raised PostBack[^]

Erdinc2713-Dec-10 23:46

Erdinc27

13-Dec-10 23:46

hey Hiren..thanks for the reply..i changed as u said and now it adds first parameter but not second parameter??
so why it happens ?

vemedya.com

Hiren solanki13-Dec-10 23:55

13-Dec-10 23:55

erdinc27 wrote:
cmmd.Parameters.AddWithValue("@yetkili1", System.Data.SqlDbType.NVarChar).Value = fir.yetkili1;

You have used blockquoted way to add parameter with value.
But AddWithValue having format of AddWithValue(string Parametername,object value)

Your statement must generate compile time error I think,

Use Like

cmmd.Parameters.AddWithValue("@yetkili1",fir.yetkili1);

Regards,
Hiren.
Microsoft Dynamics CRM

My Recent Article: - Way to know which control have raised PostBack[^]