data binding a simple value

[sham]

Hi to all,

I have an object that has a property numberOfFilesDe leted which is an
integer. I want to bind a label to it so that when the value changes, the
label gets updated on the screen.

I have used the following code to bind the text property of the label to the
object property.

private void WinForm_Load(ob ject sender, System.EventArg s e)
{
label1.DataBind ings.Add(new Binding("Text", directorySweepO bj,
"numberOfFilesD eleted"));
}


When I do the following :
private void button1_Click(o bject sender, System.EventArg s e)
{
directorySweepO bj.numberOfFile sDeleted =
directorySweepO bj.numberOfFile sDeleted + 1
}

I would expect the label to be updated, but it is not.

What am I doing wrong?

Sham.

[Marc Gravell]

Re: data binding a simple value

Your object needs to tell the UI that it has changed; this can be done in
two ways:

1.1 style: create a public event on your class called {propertyname}C hanged,
and call this event when your values change

2 style: implement the INotifyProperty Changed interface, and call this event
(specifying the name of the property) when the values change

Following is an example of the latter:

public class MyClass : INotifyProperty Changed {
private int someField;
public int SomeProperty {
get {
return someField;
}
set {
if (someField != value) {
someField = value;
OnPropertyChang ed("SomePropert y"); // oh for missing the
nameof(SomeProp erty) {or nameof(method)? } function...
}
}
}
protected void OnPropertyChang ed(string propertyName) {
if (PropertyChange d != null)
PropertyChanged (this, new
PropertyChanged EventArgs(prope rtyName));
}
public event PropertyChanged EventHandler PropertyChanged ;
}

[sham]

Re: data binding a simple value

Hi Marc,

Thanks for the reply.

I just started looking at C# last month in my spare time. So it looks like I
completely misunderstood databinding. I thought that was the whole point of
it (i.e. some sort of subject-observer pattern), where by specifying the
binding would handle the updating, registering of observer, notification
etc.

The code I have seen in the past with databinding was always with dataSets
and not with object properties.

So, I still need the data binding code -> label1.DataBind ings.Add(new
Binding("Text", directorySweepO bj,
"numberOfFilesD eleted"));

and I then introduce the notification code in my object? Is that correct?

Thanks once again.
Sham.

"Marc Gravell" <mgravell@rm.co m> wrote in message
news:uf0XvAmJGH A.3224@TK2MSFTN GP09.phx.gbl...[color=blue]
> Your object needs to tell the UI that it has changed; this can be done in
> two ways:
>
> 1.1 style: create a public event on your class called
> {propertyname}C hanged, and call this event when your values change
>
> 2 style: implement the INotifyProperty Changed interface, and call this
> event (specifying the name of the property) when the values change
>
> Following is an example of the latter:
>
> public class MyClass : INotifyProperty Changed {
> private int someField;
> public int SomeProperty {
> get {
> return someField;
> }
> set {
> if (someField != value) {
> someField = value;
> OnPropertyChang ed("SomePropert y"); // oh for missing
> the nameof(SomeProp erty) {or nameof(method)? } function...
> }
> }
> }
> protected void OnPropertyChang ed(string propertyName) {
> if (PropertyChange d != null)
> PropertyChanged (this, new
> PropertyChanged EventArgs(prope rtyName));
> }
> public event PropertyChanged EventHandler PropertyChanged ;
> }
>[/color]

[Marc Gravell]

Re: data binding a simple value

Correct;

IIRC DataSets already include this functionality, which is why you haven't
seen it so far. If you think about it. it makes sense: you don't want the UI
constantly probing your objects to see which properties have changed.

For ref, if you bing to a BindingSource instead (which sits between the UI
and the objects) you can call ResetBindings() on the source to force a
re-read from the object (e.g. when you think it has changed), but IMO it is
better to use notification - this avoids a lot of problems.

Marc