Introduction
Windows Forms DataGrid as supplied supports two column
types:
- DataGridTextBoxColumn for editing Strings and
- DataGridBoolColumn for editing Booleans
Of course the Windows Forms Library developers realized
that this would not be sufficent so they provided a base class
(DataGridColumnStyle) that can be used to implement additional column types.
This article discusses the enhancement of the DataGrid with new column types to
allow the editing of a wide range of data types. The source for these
enhancements is released to the public domain as part of the
SekosPD.Windows.Forms library.
Demo Application
The screen grab above shows a simple demonstration application that
allows the input of the contributors for a set of scientific fields. The dataset
schema is shown below. Each contributor has photo column and a number of
property columns for dates of birth and death and colour code.
To keep the sample simple, the data is persisted by
writing the DataSet to disk as an XmlDocument. In a real application, DataSet
changes would of course be persisted to a Data Tier- probably a database such as
Microsoft SQLServer.
New Column Styles
For this demo, we'll be augmenting the column types
with:
- DataGridDataPictureColumn for editing Pictures and
- DataGridPropertyEditorColumn for editing pretty
well any other data type
Because the AgileStudio product from which this code is derived is an Add-In for
Visual Studio, it is able to override the standard collection editor for
ColumnStyles. Thus the Add dropdown lists all the column styles available.
Indeed the designer is also overidden to allow columns to be added to a DataGrid
with Drag and Drop.
Because the demo in this article is standalone, you
will only see the two standard column styles in your editor and will have to
manually add the appropriate code. (One way to do this is to add a standard
DataGridTextBoxColumn and then change its type afterwards in the code window.
Once you have done this you will be able to change properties such as Mapping in
the editor.) If you are interested in how to avoid this, let me know and I'll
cover it in a subsequent article.
Friend
WithEvents DataGridPropertyEditorColumn1
As
SekosPD.Windows.Forms.DataGridPropertyEditorColumn
...
Me.DataGridPropertyEditorColumn1
= New
SekosPD.Windows.Forms.DataGridPropertyEditorColumn
...
<System.Diagnostics.DebuggerStepThrough()>
Private Sub
InitializeComponent()
...
'
'DataGridPropertyEditorColumn1
'
Me.DataGridPropertyEditorColumn1.HeaderText
= "Born"
Me.DataGridPropertyEditorColumn1.MappingName
= "Born"
Me.DataGridPropertyEditorColumn1.NullText
= ""
Me.DataGridPropertyEditorColumn1.PropertyType
=
GetType(System.DateTime)()
Me.DataGridPropertyEditorColumn1.UseStringAsUnderlyingType
= False
Me.DataGridPropertyEditorColumn1.Width
= 150
Editing Pictures
This is done by having a column of type DataGridDataPictureColumn. A
right mouse click will bring up a context menu to allow the transfer of images
via the clipboard or to allow the pasting of an image from a file.
Currently ADO.NET only supports a small range
of data types. For this reason the picture field is encoded as base64Binary
which is equivalent in .NET types to an array of byte. Internal functions
ByteArrayToImage and ImageToByteArray handle the required conversions.
If you are using Microsoft SQLServer as your
data tier, make sure you are handling base64 binary correctly. For example if
you are getting the data as XML, use a statement like the following:
SELECT ... FOR XML EXPLICIT,BINARY BASE64
Editing nearly any other Data Type
This is accomplished by having a column of
type DataGirdPropertyEditorColumn. The DataGridPropertyEditorColumns in this
example makes use of two editors- one for System.DateTime and one for
System.Drawing.Color. Both these were implemented by Microsoft as DropDowns.
This is the most common method but editors for some types, for example
System.Drawing.Font, are implemented as Popup Dialogs.
The really nice thing is that there are dozens
of UITypeEditors and TypeConverters included with .NET as standard. These are
needed to drive the PropertyGrid that is used to edit properties in Visual
Studio. You get to leverage all this functionality with almost no work. Just set
the PropertyType property in your Column as appropriate and everything else is
automatic. It is also fairly easy to implement a TypeConverter and UITypeEditor
for a type that you have written yourself.
There is one other property of
DataGridPropertyEditorColumn that is important to mention:
UseStringAsUnderlyingType. This should be set to true when binding to a DataSet
if the type that you are binding is not one of the types supported by DataSet
(For example System.DateTime is supported, but System.Drawing.Color is not.) If
you are binding to a different data source that does not have this restriction,
you can set alwaysUseStringAsUnderlyingType to false for more efficent data
transfer.
Points of Interest
DataGridDataPictureColumn and
DataGridPropertyEditorColumn employ DataPicture and PropertyEditor internally to
handle a cell in edit mode. Both these controls can be used independently
outside the DataGrid using standard simple data binding.
The source code for the SekosPD.Windows.Forms
library is released to the public domain and is available here. Reference style
documentation for the library source will be available here. You may also want
to read the article "Edit Almost Anything - Part I", which examines other
controls as well as the DataGrid.
The code released with this article is based
on a portion of the AgileStudio product, which extends Visual Studio. Check out
the free evaluation at http://www.sekos.com/
which automatically maintains the datasets and SQL StoreProcs required for a
specific user interface (for Windows or Web applications).
Conclusion
The code in this article is currently in
VB.NET. If you would like a version in C#, let me know. I would also like to
examine some of the really neat things that you can do with UITypeEditors
including CollectionEditors to make the DataGridPropertyEditorColumn really fly.
If you would like an article about this, get in touch.
Join the conversation! Your thoughts help the community grow.