Question about Databinding - binding controls to members of my business object.

[Michael.Suarez]

Let's suppose I have an instance of MyClass, which has the properties
MyText1 and MyText2, and sets the values of MyText1 and MyText2 to 'A'
and 'B' in it's constructor.

Let's also suppose I have a Form with textBox1, textBox2, btnShowValue,
and btnNew.

Let's also suppose I have this code.

//member of Form
MyClass MyObject;

//in Form Load Method:
{
MyObject = new MyClass();

textBox1.DataBi ndings.Add("Tex t", MyObject, "MyText1");
textBox2.DataBi ndings.Add("Tex t", MyObject, "MyText2");
}

//in btnShowValue Click Method
{
MessageBox.Show (MyObject.MyTex t1);
MessageBox.Show (MyObject.MyTex t2);
}

//in btnNew Click Method
{
MyObject = new MyClass();
}
If I were to run this program, I could start typing into Textbox1 and
Textbox2. Then if I were to click btnShowValue, I would see
MessageBoxes with the values of what I just typed, being as the
textboxes are bound to the properties of the object.

BUT, If I were to click btnNew, I would expect Textbox1 and Textbox2 to
revert to the default values 'A' and 'B'.

They do not. They stay the same. And clicking btnShowValues gives you
'A' and 'B' from now on, no matter what you type in the textboxes.

My question is WHY? What am I missing here?
and How do i alter this code so that it works the way I want it to?

[Nicholas Paldino [.NET/C# MVP]]

Michael,

When you pass the MyObject reference to the Add method, it will remember
the reference, but it knows nothing about the variable or when it changes.

What you would have to do is remove the binding, and then add a new one,
with a reference to the new class instance.

Hope this helps.
--
- Nicholas Paldino [.NET/C# MVP]
- mv*@spam.guard. caspershouse.co m

<Mi************ @gmail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .

Let's suppose I have an instance of MyClass, which has the properties
MyText1 and MyText2, and sets the values of MyText1 and MyText2 to 'A'
and 'B' in it's constructor.

Let's also suppose I have a Form with textBox1, textBox2, btnShowValue,
and btnNew.

Let's also suppose I have this code.

//member of Form
MyClass MyObject;

//in Form Load Method:
{
MyObject = new MyClass();

textBox1.DataBi ndings.Add("Tex t", MyObject, "MyText1");
textBox2.DataBi ndings.Add("Tex t", MyObject, "MyText2");
}

//in btnShowValue Click Method
{
MessageBox.Show (MyObject.MyTex t1);
MessageBox.Show (MyObject.MyTex t2);
}

//in btnNew Click Method
{
MyObject = new MyClass();
}
If I were to run this program, I could start typing into Textbox1 and
Textbox2. Then if I were to click btnShowValue, I would see
MessageBoxes with the values of what I just typed, being as the
textboxes are bound to the properties of the object.

BUT, If I were to click btnNew, I would expect Textbox1 and Textbox2 to
revert to the default values 'A' and 'B'.

They do not. They stay the same. And clicking btnShowValues gives you
'A' and 'B' from now on, no matter what you type in the textboxes.

My question is WHY? What am I missing here?
and How do i alter this code so that it works the way I want it to?

[Marc Gravell]

An alternative to the above is to bind not the the object, but to a
BindingSource; this acts as a proxy between the UI and one-or-more objects
(potentially allowing cursor navigation, but that's an aside for this
scenario).

All you then do is change the object in the BindingSource, leaving you to do
your bindings in the designer (if you so choose).

I posted a full working example of this to this group previously - 8th Dec
2005, titled "Re: Binding data to form controls".

Marc

<Mi************ @gmail.com> wrote in message
news:11******** **************@ f14g2000cwb.goo glegroups.com.. .

Let's suppose I have an instance of MyClass, which has the properties
MyText1 and MyText2, and sets the values of MyText1 and MyText2 to 'A'
and 'B' in it's constructor.

Let's also suppose I have a Form with textBox1, textBox2, btnShowValue,
and btnNew.

Let's also suppose I have this code.

//member of Form
MyClass MyObject;

//in Form Load Method:
{
MyObject = new MyClass();

textBox1.DataBi ndings.Add("Tex t", MyObject, "MyText1");
textBox2.DataBi ndings.Add("Tex t", MyObject, "MyText2");
}

//in btnShowValue Click Method
{
MessageBox.Show (MyObject.MyTex t1);
MessageBox.Show (MyObject.MyTex t2);
}

//in btnNew Click Method
{
MyObject = new MyClass();
}
If I were to run this program, I could start typing into Textbox1 and
Textbox2. Then if I were to click btnShowValue, I would see
MessageBoxes with the values of what I just typed, being as the
textboxes are bound to the properties of the object.

BUT, If I were to click btnNew, I would expect Textbox1 and Textbox2 to
revert to the default values 'A' and 'B'.

They do not. They stay the same. And clicking btnShowValues gives you
'A' and 'B' from now on, no matter what you type in the textboxes.

My question is WHY? What am I missing here?
and How do i alter this code so that it works the way I want it to?

[Michael.Suarez]

Thanks for the responses.

It appears as though the BindingSource is new to 2005. My project uses
a .Net API that was created in 1.1 and not compatible in a 2.0 project,
therefore restricting me to use VS 2003.

Anything comparable to a BindingSource in 2003?

[Marc Gravell]

Not as far as I know. IIRC, you didn't state 1.1 in the original question so
I assumed 2.0; in this case you have to do it the hard way (as per the other
poster).

Personally, my recommendation is that it is better to invest time making an
app 2005 compatible than to invest time working around 2003 limitations that
are addressed (often very gracefully) in 2005 - however, I appreciate that
this is not always achievable, particularly if you only want to make a minor
change.

Marc

<Mi************ @gmail.com> wrote in message
news:11******** **************@ g49g2000cwa.goo glegroups.com.. .

Thanks for the responses.

It appears as though the BindingSource is new to 2005. My project uses
a .Net API that was created in 1.1 and not compatible in a 2.0 project,
therefore restricting me to use VS 2003.

Anything comparable to a BindingSource in 2003?

[Michael.Suarez]

Appreciate the feedback.

According to these responses, these are the changes I've made:

//in Form Load Method:
{
MyObject = new MyClass();

SetDataBindings ();
}

//in btnNew Click Method
{
MyObject = new MyClass();

SetDataBindings ();
}

//in SetDataBindings Method
{
foreach(Control ctrl in this.Controls)
{
ctrl.DataBindin gs.Clear();
}
textBox1.DataBi ndings.Add("Tex t", MyObject, "MyText1");
textBox2.DataBi ndings.Add("Tex t", MyObject, "MyText2");
}

So that works great and eliminates my initial problem. Thanks!
But here is another issue...
lets say I add another button. In it's click event method, I have this
code:
{
MyObject.MyText 1 = "C";
MyObject.MyText 2 = "D";
}

I would expect the values in the textBoxes to change upon clicking this
button. But they don't!
However, if I start typing into textBox1 then place my cursor in
textBox2, textBox2 all of a sudden displays "D".

So somehow, the application knew to change the value in at least one of
the textBoxes, but only after changing one textbox and putting my
cursor the other.
Why is this? How can I get my application to know to change the values
in both textboxes immediately upon updating MyText1 and MyText2?

[Marc Gravell]

This illustrates my previous point about 1.1 vs 2.0.

The "simple" answer (from my external viewpoint) is to move to 2.0 and
implement the INotifyProperty Changed interface (ammending your setters
accordingly). I don't know of a good way to do this in 1.1, short of cloning
the INotifyProperty Changed interface and using it to reset your bindings
manually (i.e. catch the event and reset your bindings for the object). This
approach would at least smooth the transition from 1.1 to 2.0, as you would
just discard your local version of INotifyProperty Changed and your event
handler, and hopefully things would continue to just work.

The INotifyProperty Changed interface is designed to deal with *exactly* this
scenario in a generic manner, and integrates tightly into bindings.

Marc

<Mi************ @gmail.com> wrote in message
news:11******** **************@ g49g2000cwa.goo glegroups.com.. .

Appreciate the feedback.

According to these responses, these are the changes I've made:

//in Form Load Method:
{
MyObject = new MyClass();

SetDataBindings ();
}

//in btnNew Click Method
{
MyObject = new MyClass();

SetDataBindings ();
}

//in SetDataBindings Method
{
foreach(Control ctrl in this.Controls)
{
ctrl.DataBindin gs.Clear();
}
textBox1.DataBi ndings.Add("Tex t", MyObject, "MyText1");
textBox2.DataBi ndings.Add("Tex t", MyObject, "MyText2");
}

So that works great and eliminates my initial problem. Thanks!
But here is another issue...
lets say I add another button. In it's click event method, I have this
code:
{
MyObject.MyText 1 = "C";
MyObject.MyText 2 = "D";
}

I would expect the values in the textBoxes to change upon clicking this
button. But they don't!
However, if I start typing into textBox1 then place my cursor in
textBox2, textBox2 all of a sudden displays "D".

So somehow, the application knew to change the value in at least one of
the textBoxes, but only after changing one textbox and putting my
cursor the other.
Why is this? How can I get my application to know to change the values
in both textboxes immediately upon updating MyText1 and MyText2?

[Michael.Suarez]

Yeah, unfortunately I can't move to 2.0 as the 3rd party .NET API I am
using isn't compatible. But this is good stuff. I'm sure I will
eventually come across this again in 2005, in which case I will
definately keep INotifyProperty Changed in mind.

I still feel like there is still something else I can do here.
Something gets triggered when I change one textBox and put the cursor
in the other. If I can only figure out what it is... Then I could
trigger my own PropertyChanged method in all of the "set" portions of
my properties, which could then trigger an event that could tell the
textBoxes that they need to update.

[Bart Mermuys]

Hi,

<Mi************ @gmail.com> wrote in message
news:11******** **************@ g49g2000cwa.goo glegroups.com.. .

Appreciate the feedback.

According to these responses, these are the changes I've made:

//in Form Load Method:
{
MyObject = new MyClass();

SetDataBindings ();
}

//in btnNew Click Method
{
MyObject = new MyClass();

SetDataBindings ();
}

//in SetDataBindings Method
{
foreach(Control ctrl in this.Controls)
{
ctrl.DataBindin gs.Clear();
}
textBox1.DataBi ndings.Add("Tex t", MyObject, "MyText1");
textBox2.DataBi ndings.Add("Tex t", MyObject, "MyText2");
}

So that works great and eliminates my initial problem. Thanks!
But here is another issue...
lets say I add another button. In it's click event method, I have this
code:
{
MyObject.MyText 1 = "C";
MyObject.MyText 2 = "D";
}

If you're using NET1.1 you need to have similar named events for each
property (PropertyName+" Changed"), then the UI will refresh when a property
changes, eg.:

public class MyClass
{
private string myText1 = "";

public EventHandler MyText1Changed; //it needs to be EventHandler

public string MyText1
{
get { return myText1; }
set
{
if ( myText1 != value )
{
myText1 = value;
if ( MyText1Changed! =null )
MyText1Changed( this, EventArgs.Empty );
}
}

}

HTH,
Greetings

I would expect the values in the textBoxes to change upon clicking this
button. But they don't!
However, if I start typing into textBox1 then place my cursor in
textBox2, textBox2 all of a sudden displays "D".

So somehow, the application knew to change the value in at least one of
the textBoxes, but only after changing one textbox and putting my
cursor the other.
Why is this? How can I get my application to know to change the values
in both textboxes immediately upon updating MyText1 and MyText2?

[Michael.Suarez]

Thanks for the info! But this alone didn't solve my problem.

Adding this code gave me a nice MyText1Changed Event. But just having
the event didn't update the UI.
I need the code that will basically tell the textBoxes:
"Hey, the data you are binded to has changed! Update yourselves and
display your new Text values!"

If I had that code, I could certainly put it in the method for my
MyText1Changed event.

I am assuming that there is some way of doing this based on the fact
that if I change textBox1 and put the cursor textBox2, textBox2 all of
a sudden diplays it's new Text value. What is making it display it's
new value? That is what I need. A way of accessing and triggering
whatever it is that makes textBox2 display it's new Text value.

Thanks for the help so far. I feel like the solution is almost there.