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Fundamental question about bound controls

I have a WinForm with controls bound to a typed recordset that was generated
by the Dataset Designer. There are several ComboBox controls with their
DataSource bound to different lookup tables. Everything is working fine,
except when I need to handle a null default value in the data record coming
from the database. I want the combo whose SelectedValue is bound to that
field to display the "default" entry in the combo in this case. I tried the
following code:

if (rowService.IsD efaultCourierNu ll()) rowService.Defa ultCourier = 0;

If the branch is taken and the DefaultCourier value is changed, *all* the
bound controls go blank. I've tried placing this statement alternatively
before or after doing the Refresh of the CurrentyManager . No difference.
The following statement, placed *after* the refresh, *does* work:

if (rowService.IsD efaultCourierNu ll()) cboCourier.Sele ctedIndex = 0;

I'm new to WinForms, and it seems like there's something fundamental about
binding that I don't understand. What is the correct way to alter values in
the source DataRow when those values are bound to controls? Is changing the
value in the bound control the correct approach?
Nov 17 '05 #1
4 1765
What is the "rowService " object? What does the "IsDefaultCouri erNull()"
method do? It's not part of the framework that I can find. In fact, a google
search on IsDefaultCourie rNull returned nothing.

When you provide sample code, please provide some context with which it
makes sense to us.

Pete

"kaborka" <ka*****@discus sions.microsoft .com> wrote in message
news:69******** *************** ***********@mic rosoft.com...
I have a WinForm with controls bound to a typed recordset that was generated by the Dataset Designer. There are several ComboBox controls with their
DataSource bound to different lookup tables. Everything is working fine,
except when I need to handle a null default value in the data record coming from the database. I want the combo whose SelectedValue is bound to that
field to display the "default" entry in the combo in this case. I tried the following code:

if (rowService.IsD efaultCourierNu ll()) rowService.Defa ultCourier = 0;

If the branch is taken and the DefaultCourier value is changed, *all* the
bound controls go blank. I've tried placing this statement alternatively
before or after doing the Refresh of the CurrentyManager . No difference.
The following statement, placed *after* the refresh, *does* work:

if (rowService.IsD efaultCourierNu ll()) cboCourier.Sele ctedIndex = 0;

I'm new to WinForms, and it seems like there's something fundamental about
binding that I don't understand. What is the correct way to alter values in the source DataRow when those values are bound to controls? Is changing the value in the bound control the correct approach?

Nov 17 '05 #2

Sorry. rowService is of a typed DataRow class generated by the DataSet
Designer. The Designer generates properties for accessing the column values
in the row. rowService.Defa ultCourier is the same as
rowService["DefaultCourier "] except the property is typed as Int32 by the
Designer. Likewise, the Designer generates methods for testing nullable
columns: rowService.IsDe faultCourierNul l() is the same as
(rowService["DefaultCourier "] == null).

"Pete Davis" wrote:
What is the "rowService " object? What does the "IsDefaultCouri erNull()"
method do? It's not part of the framework that I can find. In fact, a google
search on IsDefaultCourie rNull returned nothing.

When you provide sample code, please provide some context with which it
makes sense to us.

Pete

"kaborka" <ka*****@discus sions.microsoft .com> wrote in message
news:69******** *************** ***********@mic rosoft.com...
I have a WinForm with controls bound to a typed recordset that was

generated
by the Dataset Designer. There are several ComboBox controls with their
DataSource bound to different lookup tables. Everything is working fine,
except when I need to handle a null default value in the data record

coming
from the database. I want the combo whose SelectedValue is bound to that
field to display the "default" entry in the combo in this case. I tried

the
following code:

if (rowService.IsD efaultCourierNu ll()) rowService.Defa ultCourier = 0;

If the branch is taken and the DefaultCourier value is changed, *all* the
bound controls go blank. I've tried placing this statement alternatively
before or after doing the Refresh of the CurrentyManager . No difference.
The following statement, placed *after* the refresh, *does* work:

if (rowService.IsD efaultCourierNu ll()) cboCourier.Sele ctedIndex = 0;

I'm new to WinForms, and it seems like there's something fundamental about
binding that I don't understand. What is the correct way to alter values

in
the source DataRow when those values are bound to controls? Is changing

the
value in the bound control the correct approach?


Nov 17 '05 #3
Well, you're going to have to change the way the ComboBox represents the
data without actually altering the data. If you alter the data, then that
alteration will be propagated across all controls bound to the same
datasource from the same BindingContext.

What you'll probably have to do is not automatically bind the data and
handle movement between the ComboBox and DataSet by hand.

Pete

"kaborka" <ka*****@discus sions.microsoft .com> wrote in message
news:D4******** *************** ***********@mic rosoft.com...

Sorry. rowService is of a typed DataRow class generated by the DataSet
Designer. The Designer generates properties for accessing the column values in the row. rowService.Defa ultCourier is the same as
rowService["DefaultCourier "] except the property is typed as Int32 by the
Designer. Likewise, the Designer generates methods for testing nullable
columns: rowService.IsDe faultCourierNul l() is the same as
(rowService["DefaultCourier "] == null).

"Pete Davis" wrote:
What is the "rowService " object? What does the "IsDefaultCouri erNull()"
method do? It's not part of the framework that I can find. In fact, a google search on IsDefaultCourie rNull returned nothing.

When you provide sample code, please provide some context with which it
makes sense to us.

Pete

"kaborka" <ka*****@discus sions.microsoft .com> wrote in message
news:69******** *************** ***********@mic rosoft.com...
I have a WinForm with controls bound to a typed recordset that was

generated
by the Dataset Designer. There are several ComboBox controls with their DataSource bound to different lookup tables. Everything is working fine, except when I need to handle a null default value in the data record

coming
from the database. I want the combo whose SelectedValue is bound to that field to display the "default" entry in the combo in this case. I tried
the
following code:

if (rowService.IsD efaultCourierNu ll()) rowService.Defa ultCourier = 0;

If the branch is taken and the DefaultCourier value is changed, *all*
the bound controls go blank. I've tried placing this statement alternatively before or after doing the Refresh of the CurrentyManager . No difference. The following statement, placed *after* the refresh, *does* work:

if (rowService.IsD efaultCourierNu ll()) cboCourier.Sele ctedIndex = 0;

I'm new to WinForms, and it seems like there's something fundamental about binding that I don't understand. What is the correct way to alter

values in
the source DataRow when those values are bound to controls? Is
changing the
value in the bound control the correct approach?


Nov 17 '05 #4
That seems pretty severe. Is there no way to alter the data in a DataSet via
code, and have the altered values appear in the controls bound to the DataSet?

"Pete Davis" wrote:
Well, you're going to have to change the way the ComboBox represents the
data without actually altering the data. If you alter the data, then that
alteration will be propagated across all controls bound to the same
datasource from the same BindingContext.

What you'll probably have to do is not automatically bind the data and
handle movement between the ComboBox and DataSet by hand.

Pete

Nov 17 '05 #5

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