asp.net ean 13 reader

asp.net ean 13 reader

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One common approach is to pass information using a query string in the URL. You will commonly find this approach in search engines. For example, if you perform a search on the Google website, you ll be redirected to a new URL that incorporates your search parameters. Here s an example: http://www.google.ca/search q=organic+gardening The query string is the portion of the URL after the question mark. In this case, it defines a single variable named ask, which contains the organic+gardening string. The advantage of the query string is that it s lightweight and doesn t exert any kind of burden on the server. Unlike cross-page posting, the query string can easily transport the same information from page to page. It has some limitations, however: Information is limited to simple strings, which must contain URL-legal characters. Information is clearly visible to the user and to anyone else who cares to eavesdrop on the Internet. The enterprising user might decide to modify the query string and supply new values, which your program won t expect and can t protect against. Many browsers impose a limit on the length of a URL (usually from 1 to 2 KB). For that reason, you can t place a large amount of information in the query string and still be assured of compatibility with most browsers. Adding information to the query string is still a useful technique. It s particularly well suited in database applications where you present the user with a list of items corresponding to records in a database, like products. The user can then select an item and be forwarded to another page with

The sort is according to the data type of the column. Numeric and date columns are ordered from smallest to largest. String columns are sorted alphanumerically without regard to case, assuming the underlying DataTable.CaseSensitive property is False (the default setting). Columns that contain binary data cannot be sorted.

detailed information about the selected item. One easy way to implement this design is to have the first page send the item ID to the second page. The second page then looks that item up in the database and displays the detailed information. You ll notice this technique in e-commerce sites such as Amazon.com.

With DataView sorting, the data is retrieved unordered from the database, and the results are sorted in memory. This is not the speediest approach (sorting in memory requires more overhead and is slower than having SQL Server do the same work), but it is more scalable when you add caching to the mix. That s because you can cache a single copy of the data and sort it dynamically in several different ways. ( 11 has much more about this essential technique.) Without DataView sorting, a separate query is needed to retrieve the newly sorted data. Figure 10-8 shows a sortable GridView with column links. Note that no custom code is required for this scenario.

The ObjectDataSource provides two options: If your select method returns a DataSet or DataTable, the ObjectDataSource can use the same automatic sorting used with the SqlDataSource. If your select method returns a custom collection, you need to provide a selection method that accepts a sort expression and performs the sorting. Once again, this behavior gives you enough flexibility to build a solution, but it s not necessarily the ideal arrangement. For example, instead of building a GetEmployees() method that can perform sorting, it might make more sense to create a custom EmployeeDetails collection class with a Sort() method. Unfortunately, the ObjectDataSource won t support this pattern. To use the sort parameter, you need to create a select method that accepts a single string parameter. You must then set the ObjectDataSource.SortParameterName property to identify the name of that parameter, as shown here: <asp:ObjectDataSource ID="sourceEmployees" runat="server" TypeName="DatabaseComponent.EmployeeDB" SelectMethod="GetEmployees" SortParameterName="sortExpression" />

To store information in the query string, you need to place it there yourself. Unfortunately, there is no collection-based way to do this. Typically, this means using a special HyperLink control, or you can use a Response.Redirect() statement like the one shown here: // Go to newpage.aspx. Submit a single query string argument // named recordID and set to 10. int recordID = 10; Response.Redirect("newpage.aspx recordID=" + recordID.ToString()); You can send multiple parameters as long as you separate them with an ampersand (&), as shown here: // Go to newpage.aspx. Submit two query string arguments: // recordID (10) and mode (full). Response.Redirect("newpage.aspx recordID=10&mode=full"); The receiving page has an easier time working with the query string. It can receive the values from the QueryString dictionary collection exposed by the built-in Request object, as shown here: string ID = Request.QueryString["recordID"]; Note that information is always retrieved as a string, which can then be converted to another simple data type. Values in the QueryString collection are indexed by the variable name.