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Chapter Twenty Four – SQL Server

Visual Basic .NET

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When you close the programme down and then reopen it, however, the record will be back

again!

This is because you’re not doing anything to the underlying database – DataTables and Datasets

are disconnected from the database. So we need to write some code to reconnect, and then

update.

Add a button to your form. Change the Name property to btnUpdate. Change the Text property

to Update Changes. Double click your button to open up its code stub.

The button, then, needs to do two things: issue the Update command against the underlying

database, and refresh the connection.

Add the following two lines to your button code:

data_adapter.Update( CType(binding_source.DataSource, DataTable) )

Get_DGV_Data( data_adapter.SelectCommand.CommandText )

The first line is the one that updates the database. Its done simply by typing the word Update

after the name of your Data Adapter. In between the round brackets, though, you have to tell it

what it is you’re updating. Because we have a binding source object, we have to specify the

DataSource property:

binding_source.DataSource

However, the Data Adapter doesn’t know what to do with this, so you have to convert it to a

Type that it does understand – a DataTable:

CType( binding_source.DataSource, DataTable )

The CType part means “Convert to Type”. In between the round brackets, you add what it is

you’re trying to convert. After a comma, you add the Type you want to convert to, a DataTable

for us. So we’re saying, “Convert the DataSource of the BindingSource object to a DataTable”.

The second line calls our Get_DGV_Data( ) Sub again. Notice how we’re getting the SQL

command, though:

data_adapter.SelectCommand.CommandText

So the Data Adapter has a SelectCommand property. This in turn has a CommandText

property. The CommandText is a SQL Command, and it already knows what to do – get all the

records from the database again.

Run your programme and try it out. You should now be able to add records, close the

programme down, and still see them there. You should also be able to delete a row. When you

click your Update Changes button, the row will be deleted from the database as well as the Data

Table.

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Chapter Twenty Four – SQL Server

Visual Basic .NET

332

Get Cell Data from A DataGridView

Another thing you can do with programming code is to get the values of all the cells from a

selected row. You could then pass these values on to a second form for further processing, or

just display that person’s details on a label or in a text box. Let’s see how to do that.

Add another button to your form. Change the Name to btnSelected, and the Text to Get

Selected Row. Double click the button to get at the code.

We need to set up some variables for this to work. So add the following to your button code:

Dim rowCount As Integer

Dim i As Integer

Now add the following line:

rowCount = DataGridView1.CurrentRow.Cells.Count

What we’re going to do is to loop round all the cells in the row we have selected, and get each

value. So we need to know how many cells there are. Quite handily, there’s a property of

DataGridViews that allows you to get the Current Row, and count how many cells it has.

Which is what the above line does.

Now add the following For loop:

For i = 0 To rowCount – 1

MsgBox( DataGridView1.CurrentRow.Cells(i).Value )

So we’re going from 0 to the RowCount, minus 1. The code for the loop then uses the loop

counter to access the values at these positions in the Row:

DataGridView1.CurrentRow.Cells(i).Value

Run your programme and test it out. Select an entire row by clicking in the Row header (circled

in red in a previous image). This selects the entire row. Now click your “Get Selected Row”

button. You should see something like this:

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Chapter Twenty Four – SQL Server

Visual Basic .NET

333

To finish off this section, try these exercises.

Exercise

Build up a string in your For loop, so that the message box displays the following:

Make sure you miss the ID cell out!

Exercise

Return to Design View. Click on your DataGridView control. Have a look at the properties area

on the right, and explore the long list of properties available to the control. In particular, have a

look at these properties:

AlternatingRowsDefaultCellStyle

AutoSizeColumnsMode

CellBorderStyle

Default Cell Size

Try to design a form like ours below:

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Notice that we’ve made the Column headers bold, centred everything, and had alternate colours

for each row.

But we’ll leave DataGrids there, and move on. Explore them further, though – they are quite

handy for displaying data!

Chapter Twenty Five – Picture Viewer

Visual Basic .NET

335

Picture Viewer – A Project

In this section, you’ll create your very own Picture Viewer. It will look like this:

Down the left hand side, we have a ListView control. This allows us to display thumbnails of

our chosen images. When you click an image in the ListView, the full size image appears on

the right. If the image is too big for the form, scroll bars will appear. Our programme also has

rudimentary zoom ability. When you right click the big image, the picture becomes smaller.

When you left click the image, it will become bigger. You’ll learn to use the following controls:

ListView

ImageList

Panels

Picture Box

Open File Dialogue Box

Let’s make a start.

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Adding the Controls to the Form

Start a new project. Make your Form nice and big. We made ours 950 wide by 800 high. Add a

Panel control to the form. This can be found in the toolbox, in the Containers section:

Draw the Panel any size you like. When you do, you’ll see that it has a Move icon:

With the Panel selected, set the following properties for it:

Location:

160, 10

Size:

750, 720

Anchor:

Top, Bottom, Left, Right

AutoScroll:

True

The Panel will hold a PictureBox control. The reason we’re adding a Panel is because the

PictureBox doesn’t have scrollbars of its own. We can dock a PictureBox to a Panel. When you

make the PictureBox’s image bigger than the Panel, the Panel will add the scrollbars

automatically.

So add a PictureBox to your Panel. (The PictureBox is under the Common category in the

Toolbox.) Just click the PictureBox once. Now draws out a PictureBox to fill your Panel.

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Set the following Properties for your PictureBox:

Dock:

Top

SizeMode:

AutoSize

Your Picture Box should now be entirely inside of your Panel, right up to the edges.

Now add a button to your Form. Change the Name property to btnLoadImages, and set the

Text to Load Images. Position the button somewhere in the top left of the form.

Just below the button, you can add a Label with the Text property of Images.

Add a ListView control to your form. The ListView is also under the Common category in the

Toolbox. Resize your ListView control, and place it under your button and Label. (We made

our Size 120, 300.) Leave the other properties on their defaults.

The next thing to add is a OpenFileDialog control. This can be found under the Dialog

category of the Toolbox. Simply double click to add one to your project. You’ll see it appear at

the bottom of the project window:

With the OpenFileDialog control selected, have a look at the Properties area on the right. Set

the Name property to oFD1, and the MultiSelect property to True.

Finally, add an ImageList control. This can be found under the Components category of the

Toolbox:

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Double click ImageList to add one to your project. Again, it will get added to the bottom of the

project Window:

With your ImageList1 control selected, set its ImageSize property to 32, 32. The ImageList

control, as its name suggests, holds a list of images. We’ll use these images as the thumbnail

images for the ListView.

Now that we have all our controls in place, we can start the coding.

Selecting Images

The first we’ll do is to launch the Open File Dialogue box. You’ve done this before, in a

previous section.

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Double click your button to get at the code stub. The first two lines of code to add will clear the

ImageList of its images, and clear the ListView. Add these two lines, then:

ImageList1.Images.Clear( )

ListView1.Clear( )

So we’re just issuing the Clear command of the two objects.

To get the Open File Dialogue box to appear, add these lines:

oFD1.InitialDirectory = "C:\"

oFD1.Title = "Open an Image File"

oFD1.Filter = "JPEGS|*.jpg|GIFS|*.gif"

Dim ofdResults As Integer = oFD1.ShowDialog( )

If ofdResults = Windows.Forms.DialogResult.Cancel Then

Exit Sub

End If

You should know what these lines do by now, as you’ve met them before. But we’re just

setting the initial directory, adding a title to the dialogue box, and then specifying the type of

files than can be opened. We have to handle the Cancel button being clicked, which is what the

rest of the lines do.

You can try it out, if you like. The dialogue box should appear when you click your button, and

you should be able to select more than one file.

As you learned earlier, though, the Open File Dialogue box doesn’t actually open files. It just

allows you to specify the names of the files you want to open.

Because you want the user to be able to load more than one file into the ListView area, you

have to get at all the file names selected. This can be done with a For … Each Loop. Add the

following lines to the ones you already have:

Try

Dim single_file As String

For Each single_file In oFD1.FileNames

MsgBox( single_file )

Catch ex As Exception

MsgBox("Error opening files")

End Try

Chapter Twenty Five – Picture Viewer

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We’ve put it in a Try … Catch block, to trap any errors. The first line sets up a string variable

that we’ve called single_file. The For … Each loop is this:

For Each single_file In oFD1.FileNames

MsgBox( single_file )

So the OpenFileDialog control has a property called FileNames. This gets you a list of all the

files that the user selected. By using For … Each you can loop round and get all the file names

(which will include the file paths). The file names will be stored in the single_file variable.

Try your programme out again. Click your button, and select a few images on your computer.

When you click the Open button, you should see the Message Box display, with all your file

names and file paths displayed.

We need all those file names and file paths. We can then pass them to the ImageList control, for

the thumbnails. But we’ll also need them for the ListView control. To store the file names and

file paths, we can use an array. Add the following to your Try … Catch block, just under “Dim

single_file As String”:

Dim num_of_files As Integer = oFD1.FileNames.Length

Dim aryFilePaths(num_of_files - 1) As String

The Length property of FileNames gets you how many files were selected. In between the

round brackets of aryFilePaths, we’re using this number to set the size of the array. We’re

deducting 1 because arrays start at zero.

Add this third variable, just below the two above:

Dim counter As Integer = 0

We can use the counter to access the array. In place of your Message Box, add this line to your

For … Each loop code:

aryFilePaths( counter ) = single_file

So the file names and paths will now be stored in the array we set up. Increment the counter on

the line just below this one:

counter = counter + 1

Your code should now look like this, though:

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