asp.net data matrix reader

asp.net data matrix reader

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public EmployeeDetails GetEmployee(int employeeID) { ... } The test page provides a list with all the employee IDs. This list control uses the GetEmployees() method through an Object data source: <asp:ObjectDataSource ID="sourceEmployeesList" runat="server" SelectMethod="GetEmployees" TypeName="DatabaseComponent.EmployeeDB"/> <asp:ListBox ID="lstEmployees" runat="server" DataSourceID="sourceEmployeesList" DataTextField="EmployeeID" AutoPostBack="True"/> When you choose an ID, the page posts back and uses a second data source to call GetEmployee(). The employeeID value is taken from the selected item in the list: <asp:ObjectDataSource ID="sourceEmployee" runat="server" SelectMethod="GetEmployee" TypeName="DatabaseComponent.EmployeeDB"/> <SelectParameters> <asp:ControlParameter ControlID="lstEmployees" Name="employeeID" PropertyName="SelectedValue" /> </SelectParameters> </asp:ObjectDataSource> The name you define for the parameter must match the parameter name you use in the method exactly. When the ObjectDataSource calls the method, it uses reflection to examine the method, and it examines the parameter names to determine the order of arguments. This system allows you to use overloaded methods, because the ObjectDataSource is able to correctly identify the overload you want based on the number of parameters you define and their names.

The GridView sorting features allow the user to reorder the results in the GridView by clicking a column header. It s convenient and easy to implement. To enable sorting, you must set the GridView. AllowSorting property to true. Next, you need to define a SortExpression for each column that can be sorted. In theory, a sort expression can use any syntax that s understood by the data source control. In practice, a sort expression almost always takes the form used in the ORDER BY clause of a SQL query. That means the sort expression can include a single field or a list of comma-separated fields, optionally with the word ASC or DESC added after the column name to sort in ascending or descending order. Here s how you could define the FirstName column so it sorts by alphabetically ordering rows by first name: <asp:BoundField DataField="FirstName" HeaderText="First Name" SortExpression="FirstName"/> Note that if you don t want a column to be sort-enabled, you simply don t set its SortExpression property.

The data types are not used in the matching process instead, the ObjectDataSource will attempt to convert the parameter value into the data type of the matching parameter using the appropriate type converter for that data type. If this process fails, an exception is raised.

You can interact with session state using the System.Web.SessionState.HttpSessionState class, which is provided in an ASP.NET web page as the built-in Session object. The syntax for adding items to the collection and retrieving them is basically the same as for adding items to the view state of a page. For example, you might store a DataSet in session memory like this: Session("ds") = ds You can then retrieve it with an appropriate conversion operation: ds = Ctype(Session("ds"),DataSet)

If you use autogenerated columns, each bound column has its SortExpression property set to match the DataField property.

Now, the single employee record returned from GetEmployee() is displayed in another rich data control the DetailsView. By default, the DetailsView creates a basic table with one row for each field or property in the data item. Here s a basic declaration for the DetailsView: <asp:DetailsView ID="DetailsView1" runat="server" AutoGenerateRows="True"/> You have one more detail to fill in. The first time the page is requested, there won t be any selected value in the lstEmployees control. However, the DetailsView will still try to bind itself, so the ObjectDataSource will call GetEmployee(). The employeeID parameter is null, but the actual value that s passed is 0, because integers aren t nullable. When the GetEmployee() method executes the query, it doesn t find a matching record with an employeeID of 0. This is an error condition, and an exception is thrown. You could solve this problem by revising the GetEmployee() method to return null in this situation. However, it makes more sense to catch the binding attempt and explicitly cancel it when there s no employeeID parameter. You can do this by handling the ObjectDataSource.Selecting event and looking for the employeeID parameter in the ObjectDataSourceSelectingEventArgs.InputParameters collection, which has every parameter you re using indexed by name. protected void sourceEmployee_Selecting(object sender, ObjectDataSourceSelectingEventArgs e) { if (e.InputParameters["employeeID"] == null) e.Cancel = true; }