How To: Dismiss a Dialog Box Displayed by an Office Application with Visual Basic .NET

When you are automating an Office application from Visual Basic .NET, the Office application may display a dialog box. The dialog box causes the Visual Basic .NET application to appear to stop responding (hang) because the Visual Basic .NET application is waiting for the dialog box to be dismissed. The dialog box must be dismissed before the Visual Basic .NET application can continue.

This article discusses how to use the object models for Office applications to avoid dialog boxes during Automation. It also provides a step-by-step example of how to simulate user input to programmatically dismiss a dialog box that cannot be avoided by using the usual properties and methods that are exposed in the object models.

At times, you may want to automate an Office application but not require any user interaction with the Office application. In this case, if the Office application displays a dialog box, your application appears to stop responding until a user can dismiss the dialog box. However, a user who can dismiss the dialog box may not be near the computer.

Office applications are not designed for unattended execution. Therefore, an application that automates Office may sometimes encounter a dialog box that is displayed by the Office application. From normal testing of the application, you can usually determine which dialog boxes occur, and you can write your code to avoid those particular dialog boxes.

The following are some recommended strategies for avoiding dialog boxes while you automate an Office application:

• Determine if the property or method that you are using (the one that is causing the dialog box) has optional arguments that you can pass to it. Sometimes, by passing all arguments to the property or method, you can avoid a dialog box. For example, if you are using the Open method to open an Excel workbook and that workbook is password-protected, and you do not provide the Password argument when you call the Open method, Excel displays a dialog box that asks the user to enter the password. To avoid the dialog box, provide a value for the Password argument when you call the Open method. Similarly, when you use the Close method to close a document, you can specify the SaveChanges argument to avoid a dialog box that asks the user to save changes.For additional information on how to determine the arguments that are available for the property or method that you are calling, click the article number below to view the article in the Microsoft Knowledge Base:
  222101 HOWTO: Find and Use Office Object Model Documentation
• Study the object model of the Office application to see if a property exists that prevents certain dialog boxes. For example, the Excel Application object has AskToUpdateLinks and AlertBeforeOverwriting properties.
• Set the Application.DisplayAlerts property (in Excel, Project, or Word) or use Application.DoCmd.SetWarnings False (in Access only) to turn off the display of alert messages. Most, but not all, dialog boxes can be avoided by using this setting.
• Set the Application.FeatureInstall property (in Office 2000 and later) to handle possible This feature is not installed dialog boxes when you access a component that may not be installed on the system.
• Use the On Error statement to avoid run-time error messages that may occur, such as an error message that appears when you try to set Application.ActivePrinter when no printer driver is installed on the system.
• Test your application thoroughly to help anticipate when dialog boxes may occur. For example, you may call the SaveAs method of an Office application to save to a file. If that file already exists, a dialog box may appear and request confirmation to replace the existing file. If you modify your code to check for the file before you call the SaveAs method, you can prevent the dialog box from appearing. For example, if the file already exists, you can delete it by using the Kill function before you call the SaveAs method.

NOTE: Even if you use these techniques and carefully design your application to avoid dialog boxes, you may still be faced with a situation in which a dialog box cannot be avoided with the methods and properties that are exposed in the object model of the Office application. In such situations, it may be necessary to programmatically dismiss a dialog box by simulating user input. The following demonstration illustrates how to do this with a Visual Basic .NET application.

Sample

The steps in this section demonstrate how to create a Visual Basic .NET application to automate Word and print a document by using the PrintOut method of the Word Document object. If the default printer is configured to print to the FILE port, a call to the PrintOut method produces a dialog box that prompts the user to enter a file name. To determine if the PrintOut method causes this dialog box to appear, the Visual Basic .NET application initializes a flag variable to False before it calls the PrintOut method, then sets the flag to True after the PrintOut method. Also prior to calling PrintOut, a separate procedure is run on a new thread. That procedure waits 5 seconds and checks the value of the flag variable. If the flag is True, the procedure ends without taking further action. The document is printed and the code execution continues beyond the PrintOut method. However, if the procedure determines the flag variable is still False, it is assumed that the PrintOut method has not completed and that the delay is caused by a dialog box that is waiting for user input. The procedure then gives focus to Word and uses SendKeys to dismiss the dialog box.

NOTE: For demonstration purposes, this sample uses the PrintOut method in such a way that it displays a dialog box intentionally when it prints to a printer that is set to a FILE port. Note that the PrintOut method has two arguments, OutputfileName and PrintToFile, that you can provide to avoid this dialog box.

To create the sample, follow these steps:

1. Start Microsoft Visual Studio .NET. On the File menu, click New and then click Project. Under Project types click Visual Basic Projects, then click Windows Application under Templates. Form1 is created by default.
2. On the View menu, click Toolbox to display the toolbox and add a button to Form1.
3. Double-click Button1. The code window for the Form appears.
4. In the code window, replace the following code

       Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
   
       End Sub
   					

   with:

       Private m_oWord As Object
       Private m_sWordCaption As String
       Private m_bMethodDone As Boolean
   
       Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
           On Error GoTo ErrorHandler
           'Create a new Word instance and put text in the new document.
           m_oWord = CreateObject("Word.Application")
           m_oWord.Visible = True
           m_oWord.Documents.Add()
           m_oWord.Selection.TypeText("Hello World!")
           'Maximize the Word window so that if SendKeys is needed,
           'keys will be sent to the Word window.
           m_oWord.WindowState = 1 'wdWindowStateMaximize
           'Obtain the Word caption for use with AppActivate.
           m_sWordCaption = GetWordCaption()
           'Initialize a flag to indicate the PrintOut method is not completed.
           m_bMethodDone = False
           'Start a new thread for calling the DismissDialog function, which
           'checks the value of bMethodDone to see if the method completed.
           Dim myThread As System.Threading.Thread
           myThread = New System.Threading.Thread(AddressOf DismissDialog)
           myThread.Start()
           'Call the PrintOut method, which may prompt the user to select
           'an output file name if the default printer is set to FILE.
           m_oWord.PrintOut(Background:=False)
   Done:
           'Set a flag to indicate the method has completed.
           m_bMethodDone = True
           'Close the document and quit the Word instance.
           On Error Resume Next
           m_oWord.ActiveDocument.Close(SaveChanges:=False)
           m_oWord.Quit()
           m_oWord = Nothing
           Exit Sub
   ErrorHandler:
           Resume Done
       End Sub
   
       Private Sub DismissDialog()
           On Error Resume Next
           Dim sKeys As String
           'Pause for 5 seconds.
           System.Threading.Thread.Sleep(5000)
           'Determine if the PrintOut method is done.
           If Not m_bMethodDone Then
               'Make sure that Word has the focus before using SendKeys to it.
               Microsoft.VisualBasic.Interaction.AppActivate(m_sWordCaption)
               'Specify an output file name to create.
               sKeys = "C:\MyOutput.prn"
               'Delete the file if it already exists.
               Microsoft.VisualBasic.FileSystem.Kill(sKeys)
               'Send keystrokes to enter the output file name.
               sKeys = sKeys & "~" '~ represents the Enter key to dismiss dialog
               System.Windows.Forms.SendKeys.SendWait(sKeys)
           End If
       End Sub
   
       Private Function GetWordCaption() As String
           'This returns the caption of the Word window. For use with the
           'AppActivate function.
           Dim s As String
           On Error Resume Next
           s = m_oWord.ActiveWindow.Caption
           If Err.Number = 0 Then 'no error
               s = s & " - " & m_oWord.Caption
           Else
               s = m_oWord.Caption
           End If
           GetWordCaption = s
       End Function
   					

   NOTE: The DismissDialog procedure creates a file at C:\MyOutput.prn. You can change this in the code to a different file if desired. Also, you can customize the wait time to be greater or less than five seconds when you use the Sleep method.
   
   
5. On the Debug menu, click Start.
6. Click Button1 on the form. This automates Word, adds a new document with some text, and then sends it to the printer by using the PrintOut method. You do not see a dialog box if your printer is configured to print to a printer.
7. In Control Panel, change your default printer so that it is configured to print to the FILE port.
8. Click Button1 again and note that a dialog box appears in Word. Do not dismiss the dialog box; wait five seconds and the dialog box is programmatically dismissed. The C:\MyOutput.prn file is created.

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