create and print barcode c# The ValidationSummary Control in .NET framework

Create QR in .NET framework The ValidationSummary Control

The ValidationSummary Control
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You use this control to gather the error message strings for all the other controls on the form and display them to the end user:
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If the ShowSummary property is True (the default), the error messages are dis played within the ValidationSummary control itself.
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24:
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Web Forms and Controls
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If the ShowMessageBox property is True, the error messages are displayed in a message box. (The default value for this property is False.) To display the message box, the EnableClientScript property must be True as well. The HeaderText property is a string displayed just before the first error message, both on the page and in the message box; you typically assign it a string like Please correct the following errors. The DisplayMode property is an enumerated value that specifies how the individ ual error messages are arranged on the control or the message box. Available options are BulletList (default), List, and SingleParagraph; if you select the singleparagraph mode, you should append a suitable punctuation symbol at the end of each error message.
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The result shown in Figure 24-15 was produced by setting these properties:
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ValidationSummary1.ShowMessageBox = True
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ValidationSummary1.ShowSummary = True (the default)
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ValidationSummary1.DisplayMode = ValidationSummaryDisplayMode.BulletList
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ValidationSummary1.HeaderText = Please correct the following errors
Figure 24-15
A screen full of error messages, both in the ValidationControl and in a message box
Notice that the ErrorMessage property of the first validation control in the demo pro gram the RequiredFieldValidator associated with the txtUserName control is set to
Part VI:
Internet Applications
an empty string, and for this reason it doesn t appear in the ValidationSummary control or in the message box.
Server-Side Validation
Regardless of whether client-side scripts are enabled, all the validation controls validate their companion controls when the page is submitted to the server, without any interven tion on you part. Nevertheless, you usually explicitly perform server-side validation in a specific location in code such as in the Page_Load event or in the Click event of the button that fires the postback so that your application can take any step that is appropriate. You can force the validation of all controls by invoking the Validate method. Then you can check the page s IsValid property and, if False, iterate over all the validation con trols to detect which fields contain invalid values:
Private Sub Button1_Click(ByVal sender As Object, ByVal e As EventArgs) _ Handles Button1.Click Force the validation of all controls. Me.Validate() If Not Me.IsValid Then Dim errorCount As Integer Count how many errors were found. For Each ctrl As BaseValidator In Me.Validators If Not ctrl.IsValid Then errorCount += 1 Next Display a suitable error message. lblStatus.Text = There are & errorCount.ToString & errors." End If End Sub
Notice that the message prepared by the preceding code is displayed only if the clientside scripts have been disabled in the browser or the client-side validation has been turned off. In fact, if client-side validation is enabled, the form can t be posted back to the server until all input fields contain a valid value.
List Controls
All the controls in this group DropDownList, ListBox, RadioButtonList, CheckBoxList inherit from the ListControl class and therefore have several members in common in addition to those inherited from the WebControl base class. Like their Windows Forms counterparts, all these controls expose the Items, SelectedIndex, SelectedItem, and SelectedValue properties (this last property was added in version 1.1 of the .NET Framework), and the SelectedIndexChanged event. They also expose a few properties related to data binding that I ll cover later in the next chapter, namely the DataSource, DataMember, DataTextField, DataValueField, and DataTextFormatString properties.
24:
Web Forms and Controls
Filling the Items Collection
The Items property returns a collection of ListItem objects, each one exposing four properties: Text, Selected, Value, and Attributes. The Text property is the string dis played in the control for that item. The Value property is the item s value attribute. The Selected property is a Boolean that tells whether the element is selected or not. (It s useful with the ListBox and CheckBoxList controls, the only controls that support mul tiple selections.) The Attributes property is, of course, the collection of attributes for that item, which you can use as a repository for additional values associated with the element. You can fill the Items collection in three ways:
At design time, by clicking on the Items element of the Properties window and adding elements in the ListItem Collection Editor dialog box. Through code, by using the Add method of the Items collection; this method takes either a string or a ListItem object. By using data binding to fill the controls with the values in a DataReader, a DataTable, a DataView, or any data structure that exposes the IEnumerable interface, such as an ArrayList or a Hashtable object.
The code needed to fill a list control is similar to the code I showed you for the HtmlSelect control. For example, this code creates an array of seven radio buttons display ing the weekday names:
Private Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) _ Handles MyBase.Load If Not Page.IsPostBack Then Creating the collection of radio buttons via code. For i As Integer = 1 To 7 Dim li As New ListItem(WeekdayName(i), i.ToString) RadioButtonList1.Items.Add(li) Next End If End Sub
Regardless of the technique you adopt to fill the Items collection, you should perform this action only the first time the page is requested hence the use of the IsPostBack function in the preceding code snippet because the EnableStateView property is set to True by default. Therefore, the content of a control is automatically preserved in subsequent postbacks. In some cases, you can optimize your application s perfor mance by disabling the ViewState feature for specific controls and filling the control anytime the page is loaded. Figure 24-16 shows the demo program at design time and inside the browser. All the controls except RadioButtonList were filled using data binding, as I ll explain in the Data Binding with List Controls section in 25.
Part VI:
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