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Different techniques for filling
lists using the .NET Compact Framework
I started writing this tutorial last
week before I got sidetracked by the SQLCEDataAdapter.
In essence as I was putting together the test data for this
tutorial I realized that the technique being used to create
the SQL Server CE database was a tutorial in and of itself.
So if you have any questions about the attached code relating
to creating the test data read the
.NET Compact Frameworks & the ADO.NET Data Adapter
article where I explain how I bridged the data from an XML
data source into a SQL CE database.
So you've embraced the .NET Compact
Framework and you're nashing your teeth trying to find out
how to add items to a list or combo-box. Or you've heard
that the performance of binding the dataset to the list
is terrible! Well hopefully we can kill two birds with one
stone. In this tutorial we will investigate two techniques
to fill a combo-box and measure the performance of each.
The first technique binds a data view to the combo-box and
the second is much classier. (er a little weak in the humor
department but it is 1:30 am...)
Using a dataview
The easiest way to get table information
into a combo-box is to expose a table from a data set using
thedata view. Take a look at this code used to fill
the combo-box cbo1:
Dim oTimeIt As New TimeIt()
Dim dvTest As DataView
If sql.ceConnect Then
mFilling = True
cbo1.Items.Clear()
data.Clear()
cbo1.Visible = False
sbar.Text = "Filling combobox using dataset."
: sbar.Refresh()
oTimeIt.Start()
Dim SqlDATest As New SqlCeDataAdapter("SELECT DevbuzzID,
TestName FROM DevbuzzTable order by TestName", sql.connCE)
SqlDATest.Fill(data, "DevbuzzTable")
dvTest = New DataView(data.Tables("DevbuzzTable"))
cbo1.DataSource = dvTest
cbo1.DisplayMember = "TestName"
cbo1.ValueMember = "DevbuzzID"
oTimeIt.Finish()
Label1.Text = oTimeIt.Elapsed() & " seconds"
cbo1.Visible = True
sbar.Text = "Finished." : sbar.Refresh()
SqlDATest = Nothing
sql.Disconnect()
mFilling = False
End If
Firstly we grab the test data from the
SQL Server CE database using:
Dim SqlDATest
As New SqlCeDataAdapter("SELECT DevbuzzID, TestName
FROM DevbuzzTable order by TestName", sql.connCE)
SqlDATest.Fill(data, "DevbuzzTable")
You will notice the terrible syntax
(at least in my mind) of the data adapter fill method.
For a long time I couldn't work out why I find the data
adapter syntax confusing - then it hit me - instead of SqlDATest.Fill(data,
"DevbuzzTable") it should really be data.Fill(SqlDATest,
"DevbuzzTable") - think about it, the data
data set it being filled not the SQLDATest data
adapter. Well now that I have that little rant off my
chest we can move onto the exposing the DevbuzzTable test
data using the data view. This is the command:
dvTest = New DataView(data.Tables("DevbuzzTable"))
Now all we need to do is bind the combo-box
to the dvTest dataview. We bind the column we want
to display to the DisplayMember
property and the key we wish to return to the ValueMember
property and we're done! When you a click on the combo-box
you can access the value of the corresponding ValueMember
using the following code:
Dim row As DataRowView
= CType(cbo1.Items(cbo1.SelectedIndex), DataRowView)
MessageBox.Show(row("DevbuzzID"))
When you access the ValueMember
property you are really accessing the underlying datarow
value of the data view.
Performance!!
The performance of this technique is
pretty dismal when compared to the next technique I will
show you and I would only recommend using it for prototype
solutions such as a proof-of-concept type application.
By the by, the double firing you see on the combo-box is
the result of a beta 1 bug. I didn't use any work-around
code since I want the attached sample code to be valid for
the final release. Just add a variable to trap the first
event.
Typically on my test device (Toshiba
e570) I see an elapsed time of
about 11-13 seconds to fill a combo-box with
500 rows using the bound data view technique.
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