how to generate qr code in asp net core

how to generate qr code in asp net core

asp.net core qr code generator

When the page loads, it retrieves the records from the database and binds them to the list control. This example uses a DataReader as the data source, as shown here: protected void Page_Load(object sender, System.EventArgs e) { if (!Page.IsPostBack) { // Create the Command and the Connection. string connectionString = WebConfigurationManager.ConnectionStrings[ "Northwind"].ConnectionString; string sql = "SELECT EmployeeID, TitleOfCourtesy + ' ' + " + "FirstName + ' ' + LastName As FullName FROM Employees"; SqlConnection con = new SqlConnection(connectionString); SqlCommand cmd = new SqlCommand(sql, con); try { // Open the connection and get the DataReader. con.Open(); SqlDataReader reader = cmd.ExecuteReader(); // Bind the DataReader to the list. lstNames.DataSource = reader; lstNames.DataBind(); reader.Close(); } finally { // Close the connection. con.Close(); } } } The previous code sample creates a connection to the database, creates the command that will select the data, opens the connection, and executes the command that returns the DataReader. The returned DataReader is bound to the list box, and finally the DataReader and the connection are both closed. Note that the DataBind() method of the page or the control must be called before the connection is closed. It s not until you call this method that the actual data is extracted. The last piece of this example is the code for determining the selected items. As in the previous example, this code is quite straightforward: protected void cmdGetSelection_Click(object sender, System.EventArgs e) { Result.Text += "<b>Selected employees:</b>"; foreach (ListItem li in lstNames.Items) { if (li.Selected) Result.Text += String.Format("<li>({0}) {1}</li>", li.Value, li.Text); } } If you want to use a DropDownList, a CheckListBox, or a RadioButtonList instead of a ListBox, you need to change only the control declaration. The rest of the code that sets up the data binding remains the same.

The same approach used here for updating applies when you re performing inserts and deletes. The only difference is that you handle the Inserting and Deleting events instead.

To see this in action, it s worth considering the InsertEmployee() method, which adds an employee record and returns the newly generated unique ID value as an integer: public int InsertEmployee(EmployeeDetails emp) { ... } You don t need to use the identity value. As you ve seen already, linked data controls are bound after any updates are committed, which ensures that the updated information always appears in the linked controls. However, you might want to use the identity for another purpose, such as displaying a confirmation message. To capture this identity value, you need to define a parameter: <asp:ObjectDataSource ID="sourceEmployees" runat="server" TypeName="DatabaseComponent.EmployeeDB" DataObjectTypeName="DatabaseComponent.EmployeeDetails" SelectMethod="GetEmployees" InsertMethod="InsertEmployee" OnInserted="sourceEmployees_Inserted"> <InsertParameters> <asp:Parameter Direction="ReturnValue" Name="EmployeeID" Type="Int32" /> </InsertParameters> </asp:ObjectDataSource> Now you can retrieve the parameter by responding to the Inserted event, which fires after the insert operation is finished: protected void sourceEmployees_Inserted(object sender, ObjectDataSourceStatusEventArgs e) { if (e.Exception == null) { lblConfirmation.Text = "Inserted record " + e.ReturnValue.ToString(); } }

When the IDE first loads, it shows an initial start page. You can use various user-specific options from this page and access online information such as recent MSDN articles. But to get right to work, choose File New Website to create a new ASP.NET application. Visual Studio will then show the New Web Site dialog box (see Figure 2-1). Notice that you don t use Visual Studio s File New Project command. That s because web applications aren t projects, as you ll see later in this chapter.

You can use a similar approach to add extra parameters. For example, if your method requires a parameter with information that s not contained in the linked data control, just define it as one of the UpdateParameters and then set the value when the ObjectDataSource.Updating event fires. If you re more ambitious, you can even decide to programmatically point the ObjectDataSource to a different update method in the same class: sourceEmployees.UpdateMethod = "UpdateEmployeeStrict"

As a whole, the data source controls are a remarkable innovation for ASP .NET developers. However, you ll still run into situations where you need to step beyond their bounds or even abandon them completely. In the following sections, you ll see how to use the SqlDataSource and ObjectDataSource to deal with a common design requirement additional options in a master-details list.