Hands-On-8 Advancing with VBA

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1 Hands-On-8 Advancing with VBA Creating Event Procedures In this exercise you will create a message box that will display a welcome message to the user each time your database is opened. Before starting this exercise you should have completed Hands-on 5 and set the form frmmainmenu to be the start-up form when the database opens. Start Access and open your baccsamp.mdb database. Change the form to Design view. The entire form will automatically be selected by default. The event procedure you are going to create will be linked to the OnOpen property of the form. Later, when you are creating your own procedures, you may select a single control for which the event procedure is created. Click the Properties button on the toolbar. Microsoft Access displays the property sheet for the form, report, or control. Click the Event tab to display the Event Properties. Select the event that will trigger the event procedure - for this task you will use the On Open event property. Select [Event Procedure] from the list. Click the Build button to display the Module window. Type the event procedure code between the Sub line and the End Sub line. ho-080.doc 1 07/12/ :02

2 Click the Debug button on the top level menu and click Compile to compile the module and check for errors in the event procedure. Save changes to the module. When the form or report is open, each occurrence of the event will cause the event procedure to be called. Save the form. Close it and open it again to see your procedure working. Before the form opens you should see the message box on the screen. When you click the OK button the form will open. Functions In this exercise you will create a general function, called Confirm, that performs the same task for any action that needs confirmation. The function will return a different value depending upon the choice made by the user. Close any open objects to return to the database window. Select the Module tab and press New. The new module will automatically contain the declarations section which apply to the entire module, for example, the Option Compare Database statement. Add Option Explicit to enforce the explicit declaration of all variables in the module. NB: When you use this statement, you cannot use a variable which has not been declared. Module: Module 1 Option Compare database Option Explicit Select Insert, Procedure. Select type as function and enter the name as Confirm in the Name box. Press OK. ho-080.doc 2 07/12/ :02

3 Enter the code as shown below Module: Module 1 Public Function Confirm(strMessage As String) 'Display an important message to the user. MsgBox strmessage, vbokcancel End Function Compiling Code You need to compile all VBA code before you can use it so that Access can check that there are no errors. Click the Debug button on the top level menu and click Compile to compile the module and check for errors in the event procedure. Save the module as modutilities. Using the Function You are now going to try out the Utilities function by adding a button to a test form. Open a new form in Design View. Create a new button called cmdtestmessage. Enter the function and the question you want to use in the On Click Event property of the button - see below: Switch to form view and click the button. Your message should appear. Save the form as frmtestbuttons. ho-080.doc 3 07/12/ :02

4 Create a function that can be used to trigger an event You've already seen that using a general function can help to streamline your application's performance in many ways. For example, you may need to constantly update a set of records from different forms within your application. You could achieve this by creating a command button with an event procedure, but you would need to duplicate it many times. To cut down on repetitive code writing, you may decide to create a general function that can be used at any time. Open the modutilities Module from the database window. Create a function NewRec Enter the following Code into your new function. Public Function NewRec(strFormName As String) ' This function is used in the Click event of command buttons to open forms and create a new record. 'Using a function is often more efficient ' than repeating the same code in multiple event procedures. ' Open specified form. DoCmd.OpenForm strformname,,,, acformadd DoCmd.Maximize End Function Compile and Save the Module. Close it. Open the frmtest Buttons form. Create a new button labelled Add New Customer. Attach the function =NewRec("frmCustomers) to the OnClick field of the button. Save the form and test that the function works. (What do you expect it to do?) Linking a Sub Procedure to a command button In this exercise you will create an event sub procedure that goes through the tblcustomers table and counts the number of Wine club Members. Open the frmtestbuttons form. Create a command button called cmdcountcustomers. Label the button Customer Count. ho-080.doc 4 07/12/ :02

5 Create the following sub procedure attached to the On Click event of the command button. Private Sub CountCustomers_Click() Dim dbs As Database, rst As Recordset ' Return reference to current database. Set dbs = CurrentDb ' Open table-type Recordset object. Set rst = dbs.openrecordset("tblcustomers") MsgBox "No of Records = " & rst.recordcount rst.close Set dbs = Nothing End Sub Compile and test the procedure by switching to form view and clicking the button. (how can you check that the message box is displaying the correct count?) Create a personalised Welcome message In this exercise you will create an Input Box that will prompt the user for their name and then display a personalised message. On the form frmtest buttons, create a command button called cmdwelcome and give it the label Welcome. Create the following sub procedure attached to the On Click event of the command button. Test the button Private Sub cmdwelcome_click() Dim yourname As String ' store the value entered by the user in a variable yourname = InputBox("What is your Name?") ' display the value of the variable MsgBox "Welcome, " & yourname End Sub Input boxes can be used to get a value from the user and store it in a variable. Challenge (optional extra) This is an optional extra to help you to test your understanding of VBA. It does not contain step-by-step instructions as it is designed to make you think. Before attempting it, make sure the procedures and functions you have created so far are working correctly and that you understand them. Create a general purpose function to count the records in any table The CountMembers sub procedure can only count the records in tblmembers. It would be useful to create a general purpose function RecCount that would count the records in any table specified by the user. Where should such a function be stored? What argument needs to be passed to the function? ho-080.doc 5 07/12/ :02

6 Think about the NewRec function you created earlier. Once you have decided on the answers to the questions above, create the function. The code will be identical to the code for the CountMembers sub except that it will use a variable as the argument to the OpenRecordset method. ho-080.doc 6 07/12/ :02