Build Your Own ASP.NET 3.5 Website Using C# & VB (92 page)

Visual Basic

departmentsGrid.DataSource = _

dataSet.Tables("Departments").DefaultView

departmentsGrid.DataBind()

C#

departmentsGrid.DataSource =

dataSet.Tables["Departments"].DefaultView;

departmentsGrid.DataBind();

DefaultView Does Not Apply when Binding to a DataSet

It’s interesting to note that if you bind directly to a DataSet that contains only

one table, that table’s DefaultView will not be used; the GridView will generate

a separate DataView itself.

DataViews represent a customized view of a DataSet for sorting, filtering, searching,

editing, and navigation. When binding a GridView directly to a DataTable, the

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

DefaultView property, which is a DataView object, is accessed automatically for

us. However, if we want to enable sorting, we need to access the DataView and set

its sorting parameters.

The first step to enabling sorting is to set the AllowSorting property to True. When

we do that, the grid’s column headings become hyperlinks. Before we make those

hyperlinks work, we need to handle the grid’s Sorting event, in which we teach

the grid what to do when those links are clicked.

Set the AllowSorting property of the GridView control in
Departments.aspx
to True,

then use the designer to generate the handler for the GridView’s Sorting event.

Now, complete the code as shown here:

Visual Basic

Dorknozzle\VB\19_Departments.aspx.vb
(excerpt)

Protected Sub departmentsGrid_Sorting(ByVal sender As Object,

➥ ByVal e As System.Web.UI.WebControls.GridViewSortEventArgs)

➥ Handles departmentsGrid.Sorting

Dim sortExpression As String = e.SortExpression

If (sortExpression = gridSortExpression) Then

If gridSortDirection = SortDirection.Ascending Then

gridSortDirection = SortDirection.Descending

Else

gridSortDirection = SortDirection.Ascending

End If

Else

gridSortDirection = WebControls.SortDirection.Ascending

End If

gridSortExpression = sortExpression

BindGrid()

End Sub

Private Property gridSortDirection() As SortDirection

Get

If (ViewState("GridSortDirection") Is Nothing) Then

ViewState("GridSortDirection") = SortDirection.Ascending

End If

Return ViewState("GridSortDirection")

End Get

Set(ByVal value As SortDirection)

ViewState("GridSortDirection") = value

End Set

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End Property

Private Property gridSortExpression() As String

Get

If (ViewState("GridSortExpression") Is Nothing) Then

ViewState("GridSortExpression") = "DepartmentID"

End If

Return ViewState("GridSortExpression")

End Get

Set(ByVal value As String)

ViewState("GridSortExpression") = value

End Set

End Property

C#

Dorknozzle\CS\19_Departments.aspx.cs
(excerpt)

protected void departmentsGrid_Sorting(object sender,

GridViewSortEventArgs e)

{

string sortExpression = e.SortExpression;

if (sortExpression == gridSortExpression)

{

if(gridSortDirection == SortDirection.Ascending)

{

gridSortDirection = SortDirection.Descending;

}

else

{

gridSortDirection = SortDirection.Ascending;

}

}

else

{

gridSortDirection = SortDirection.Ascending;

}

gridSortExpression = sortExpression;

BindGrid();

}

private SortDirection gridSortDirection

{

get

{

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

if (ViewState["GridSortDirection"] == null)

{

ViewState["GridSortDirection"] = SortDirection.Ascending;

}

return (SortDirection) ViewState["GridSortDirection"];

}

set

{

ViewState["GridSortDirection"] = value;

}

}

private string gridSortExpression

{

get

{

if (ViewState["GridSortExpression"] == null)

{

ViewState["GridSortExpression"] = "DepartmentID";

}

return (string) ViewState["GridSortExpression"];

}

set

{

ViewState["GridSortExpression"] = value;

}

}

Properties

We haven’t really discussed the task of defining your own properties since

Chapter 4
, so now might be a good time for a quick refresher. By now, you should be fairly comfortable with the idea that each of your web forms is its own class,

and inherits a great deal of functionality from its parent class, Page. You’ve already

dealt with quite a few of that class’s features, such as its Load event and its

IsPostBack property.

You can define for your class properties that can be read-only, write-only, or are

able to be both read and written to. When you read data from a property, its Get

code is executed. Most of the time, this code will be quite simple, but it can be as

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535

complex as you choose to make it. In the same way, when a value is written to a

property, its Set code is executed, which can also be quite complex if you choose

to make it so.

Finally, update the BindGrid method to apply the sorting:

Visual Basic

Dorknozzle\VB\19_Departments.aspx.vb
(excerpt)

Private Sub BindGrid()

Dim conn As SqlConnection

Dim dataSet As New DataSet

Dim adapter As SqlDataAdapter

If ViewState("DepartmentsDataSet") Is Nothing Then

Dim connectionString As String = _

ConfigurationManager.ConnectionStrings( _

"Dorknozzle").ConnectionString

conn = New SqlConnection(connectionString)

adapter = New SqlDataAdapter( _

"SELECT DepartmentID, Department FROM Departments", _

conn)

adapter.Fill(dataSet, "Departments")

ViewState("DepartmentsDataSet") = dataSet

Else

dataSet = ViewState("DepartmentsDataSet")

End If

Dim sortExpression As String

If gridSortDirection = SortDirection.Ascending Then

sortExpression = gridSortExpression & " ASC"

Else

sortExpression = gridSortExpression & " DESC"

End If

dataSet.Tables("Departments").DefaultView.Sort = sortExpression

departmentsGrid.DataSource = _

dataSet.Tables("Departments").DefaultView

departmentsGrid.DataBind()

End Sub

C#

Dorknozzle\CS\19_Departments.aspx.cs
(excerpt)

private void BindGrid()

{

SqlConnection conn;

DataSet dataSet = new DataSet();

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

SqlDataAdapter adapter;

if(ViewState["DepartmentsDataSet"] == null)

{

string connectionString =

ConfigurationManager.ConnectionStrings[

"Dorknozzle"].ConnectionString;

conn = new SqlConnection(connectionString);

adapter = new SqlDataAdapter(

"SELECT DepartmentID, Department FROM Departments",

conn);

adapter.Fill(dataSet, "Departments");

ViewState["DepartmentsDataSet"] = dataSet;

}

else

{

dataSet = (DataSet)ViewState["DepartmentsDataSet"];

}

string sortExpression;

if(gridSortDirection == SortDirection.Ascending)

{

sortExpression = gridSortExpression + " ASC";

}

else

{

sortExpression = gridSortExpression + " DESC";

}

dataSet.Tables["Departments"].DefaultView.Sort = sortExpression;

departmentsGrid.DataSource =

dataSet.Tables["Departments"].DefaultView;

departmentsGrid.DataBind();

}

Execute the project again
, and test that sorting by column works as shown in Fig-

ure 12.28.

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Figure 12.28. Sorting Dorknozzle’s departments

We’ve written a lot of code here! Let’s take a look at how it works.

In order to sort the data in the grid, all we need to do is set the Sort property of the

view we’re displaying to
ColumnNameSortOrder
, where
ColumnName
is, of course, the name of the column we’re sorting, and
SortOrder
is either ASC (for ascending)

or DESC (for descending). So, if you were sorting the DepartmentID column, the Sort

property would need to be set to DepartmentID ASC or Department DESC.

This property must be set before the data binding is performed, as is shown in the

following code, which will sort the data by DepartmentID in descending numeric

order:

Visual Basic

dataTable.DefaultView.Sort = "DepartmentID DESC"

departmentsGrid.DataSource = dataTable.DefaultView

departmentsGrid.DataBind()

C#

dataTable.DefaultView.Sort = "Department DESC";

departmentsGrid.DataSource = dataTable.DefaultView;

departmentsGrid.DataBind();

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Build Your Own ASP.NET 3.5 Web Site Using C# & VB

It’s a pretty simple task to sort a DataView in code like this, but if we want to let

users sort the data on the basis of any column, in any direction, things get a little

bit more complicated. In this case, we need to remember the previous sort method

between requests.

In order to be truly user-friendly, our grid should behave like this:

■ The first time a column header is clicked, the grid should sort the data in ascending order, based on that column.