Validating domain objects

Standalone applications typically have a main window that both displays the main data over which the application operates and exposes the functionality to process that data through user interface (UI) mechanisms like menu bars, tool bars, and status bars.A non-trivial application may also display additional windows to do the following: dialog box is displayed by a function when the function needs additional data from a user to continue.Warning; ' Configure the message box to be displayed Dim message Box Text As String = "Do you want to save changes? End Select For more information on using message boxes, see Message Box, Message Box Sample, and Dialog Box Sample. When a menu item runs a function that displays a dialog box which does not require user interaction, such as an About dialog box, an ellipsis is not required." Dim caption As String = "Word Processor" Dim button As Message Box Button = Message Box Button. Although Message Box may offer a simple dialog box user experience, the advantage of using Message Box is that is the only type of window that can be shown by applications that run within a partial trust security sandbox (see Security), such as XAML browser applications (XBAPs). A dialog box is typically shown as a result of a user selecting a menu item to perform a domain-specific function, such as setting the margins of a document in a word processor.Show(message Box Text, caption, button, icon) ' Process message box results Select Case result Case Message Box Result. Windows implements a variety of reusable dialog boxes that are common to all applications, including dialog boxes for opening files, saving files, and printing. Filter = "Text documents (.txt)|*.txt"; // Filter files by extension // Show open file dialog box Nullable' Configure open file dialog box Dim dlg As New Microsoft. Default Ext = ".txt" ' Default file extension dlg. Filter = "Text documents (.txt)|*.txt" ' Filter files by extension ' Show save file dialog box Dim result? Show Dialog() ' Process save file dialog box results If result = True Then ' Save document Dim filename As String = dlg. The print dialog box, shown in the following figure, is used by printing functionality to choose and configure the printer that a user would like to print data to. The following code shows how to create, configure, and show one. Here, the code is passing default information (the current margins) to the dialog box. Owner property with a reference to the window that is showing the dialog box.Since these dialog boxes are implemented by the operating system, they can be shared among all the applications that run on the operating system, which helps user experience consistency; when users are familiar with the use of an operating system-provided dialog box in one application, they don't need to learn how to use that dialog box in other applications. Filter = "Text documents (.txt)|*.txt" ' Filter files by extension ' Show open file dialog box Dim result? Show Dialog() ' Process open file dialog box results If result = True Then ' Open document Dim filename As String = dlg. File Name End If For more information on the save file dialog box, see Microsoft. The common print dialog box is implemented as the Print Dialog class, and is located in the System. In general, you should always set the owner for a dialog box to provide window state-related behaviors that are common to all dialog boxes (see WPF Windows Overview for more information). Max Margin) Return New Validation Result(False, msg) End If ' Number is valid Return New Validation Result(True, Nothing) End Function End Class End Namespace In this code, the validation logic of a validation rule is implemented by overriding the Validate method, which validates the data and returns an appropriate Validation Result.The common open file dialog box is implemented as the Open File Dialog class and is located in the Microsoft. The following code shows how to create, configure, and show one, and how to process the result. A validation rule is a custom class that derives from Validation Rule. Controls Namespace SDKSample Public Class Margin Validation Rule Inherits Validation Rule Private _max Margin As Double Private _min Margin As Double Public Property Max Margin() As Double Get Return Me._max Margin End Get Set(By Val value As Double) Me._max Margin = value End Set End Property Public Property Min Margin() As Double Get Return Me._min Margin End Get Set(By Val value As Double) Me._min Margin = value End Set End Property Public Overrides Function Validate(By Val value As Object, By Val culture Info As Culture Info) As Validation Result Dim margin As Double ' Is a number? Try Parse(CStr(value), margin) Then Return New Validation Result(False, "Not a number.") End If ' Is in range? When a control contains invalid data, WPF will display a red border around the invalid control, as shown in the following figure.The following example shows a validation rule, Imports System. WPF does not restrict a user to the invalid control until they have entered valid data.

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In most cases, a modal dialog box allows a user to signal when they have finished with the modal dialog box by pressing either an OK or Cancel button.Yes No Cancel Dim icon As Message Box Image = Message Box Image. Most dialog boxes display and gather more complex data than the result of a message box, including text, selection (check boxes), mutually exclusive selection (radio buttons), and list selection (list boxes, combo boxes, drop-down list boxes). Default Ext = ".text"; // Default file extension dlg. File Name = "Document" ' Default file name dlg. Showing a window as a dialog box is similar to showing a normal window, although it requires additional dialog box-specific configuration.Warning ' Display message box Dim result As Message Box Result = Message Box. For these, Windows Presentation Foundation (WPF) provides several common dialog boxes and allows you to create your own dialog boxes, although the use of either is limited to applications running with full trust. Default Ext = ".txt"; // Default file extension dlg. File Name = "Document" ' Default file name dlg. Filter = "Text documents (.txt)|*.txt"; // Filter files by extension // Show save file dialog box Nullable' Configure save file dialog box Dim dlg As New Microsoft. Default Ext = ".text" ' Default file extension dlg. The entire process of instantiating, configuring, and opening a dialog box is shown in the following code.A modeless dialog box at least provides a Close button to close the dialog box, and may provide additional buttons to execute specific functions, such as a Find Next button to find the next word that matches the find criteria of a word search.Windows Presentation Foundation (WPF) allows you to create several types of dialog boxes, including message boxes, common dialog boxes, and custom dialog boxes.

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