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3.18. Add Images and Controls to the DataGridView
To create a custom column with the
DataGrid, you needed to implement the
functionality yourself by deriving a custom
DataGridColumnStyle class that would need dozens
of lines of code. The DataGridView provides a much
simpler model. In fact, you can add new columns right alongside your
data-bound columns!
Note: There''s a lot more that you can do with
theDataGridView, including adding static buttons and
images.
3.18.1. How do I do that?
In many scenarios, it''s useful to display a button
next to each row in a grid. Clicking this button can then remove a
record, add an item to a shopping cart, or call up another window
with more information. The DataGridView makes this
easy with the DataGridViewButtonColumn
class. You simply need to create a new instance, specify the button
text, and add it to the end of the grid:
'' Create a button column.
Dim Details As New DataGridViewButtonColumn( )
Details.Name = "Details"
'' Turn off data-binding and show static text.
'' (You could use a property from the table by setting
'' the DataPropertyName property instead.)
Details.UseColumnTextForButtonValue = False
Details.Text = "Details..."
'' Clear the header.
Details.HeaderText = "
'' Add the column.
DataGridView1.Columns.Insert(DataGridView1.Columns.Count, Details)
Once you''ve performed this easy task, you can
intercept the CellClick event to perform another
action (Figure 3-14 shows the result of this simple
test):
Private Sub DataGridView1_CellClick(ByVal sender As System.Object, _
ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) _
Handles DataGridView1.CellClick
If DataGridView1.Columns(e.ColumnIndex).Name = "Details" Then
MessageBox.Show("You picked " & _
DataGridView1.Rows(e.RowIndex).Cells("CustomerID").Value)
End If
End Sub
Figure 3-14. Using a button column
Creating an image column is just as easy. In this case, you simply
create and add a new DataGridViewImageColumn
object. If you want to show the same static image in each cell,
simply set the Image property with the
Image object you want to use.
A more sophisticated technique is to show a separate image for each
record. You can draw this record from a binary field in the database,
or read it from a file specified in a string field. In either case,
the technique is basically the same. First of all, you hide the
column that contains the real data (the raw binary information for
the picture, or the path to the file) by setting its
Visible property to False.
Then, you create a new DataGridViewImageColumn:
DataGridView1.DataSource = ds
DataGridView1.DataMember = "pub_info"
'' Hide the binary data.
DataGridView1.Columns("logo").Visible = False
'' Add an image column.
Dim ImageCol As New DataGridViewImageColumn( )
ImageCol.Name = "Image"
ImageCol.Width=200
DataGridView1.Columns.Add(ImageCol)
Finally, you can set the binary picture data you need:
For Each Row As DataGridViewRow In DataGridView1.Rows
'' First, you must convert the binary data to a memory stream.
'' Then, you can use the memory stream to create an Image object.
Try
Dim ImageBytes( ) As Byte = Row.Cells("logo").Value
Dim ms As New MemoryStream(ImageBytes)
Dim img As Image = Image.FromStream(ms)
'' Finally, bind the image column.
Dim ImageCell As DataGridViewImageCell = CType(Row.Cells("Image"), _
DataGridViewImageCell)
ImageCell.Value = img
'' Now you can release the original information to save space.
Row.Cells("logo").Value = New Byte( ) { }
Row.Height = 100
Catch
'' Ignore errors from invalid images.
End Try
Next
Figure 3-15 shows the
DataGridView with image data.
Figure 3-15. Using an image column
Note: In many cases, DataGridView is intelligent enough to
recognize image data types and use them seamlessly in image columns,
with no conversion required. However, if any extra work is required
(e.g., converting or removing extra header information), you need to
use the technique shown here.
3.18.2. Where can I learn more?
So, you want to do even more with the
DataGridView control? Because it is one of the key
showpieces of the new .NET Windows Forms toolkit,
there''s a lot of online documentation for the
DataGridView. Look up the index entry
"DataGridView control (Windows
Forms)" in the MSDN help, and
you''ll find nearly 100 entries detailing distinct
features you can add to solutions that use the
DataGridView!
