Friday 20 December 2019

Creating Custom Objects with Class Modules

Suppose we wanted to work with a set of related variables with VBA code.  Let's say these variables relate to a person.  The information we want to store and process may include the person's name, age and gender.   The best way to do this would be to create our own custom person object; with the above-mentioned variables as the object's properties, and any code to process or work with these properties, as the object's methods.

The advantage of creating a custom object is that a lot of related information, and the means to process it, is contained within a referenced entity that is easily accessed and used from different parts of the program.

There are two steps to creating a custom object. The first is to create a blueprint or design for the object which defines what information the object holds and the processing to be done on that information. To do this we create what is known as a Class Module. The second step is to create the actual object based on the class module - this is known as instantiation. Once the class module is in place, we can create as many instances, or objects based on the module, as we need. Hence, we may reuse the code we write in the class module over and over again.

Let's go through the steps to create a class module:

Creating a Class Module

  1. Open the database in which the class module is to be created.
  2. Click the CLASS MODULE icon in the MACROS & CODE group of the CREATE ribbon.  This opens the VBA editor ready to enter code in our new class module.
  3. Click SAVE CLASS MODULES in the FILE menu of the VBA editor.
  4. Give the new class module the name "clsPerson" when the SAVE AS dialog window opens.
    Save As dialog window

Although we haven't started to enter code, the new clsPerson Module shows up in the VBA Project in the CLASS MODULES node of the VBA Project Explorer, and in the MODULES section of the main Access Navigation Pane.

VBA Project Explorer

Access Navigation Pane

Code to Create an Instance of the Class Module

We will add code to our class module in the following section. Before doing so, however, let's look at how the class module is instantiated - ie how the blueprint becomes an actual object.

Objects are instantiated in code outside of the class module itself, where the object is to be used - this may be in the code belonging to an Access form or report, or perhaps in a conventional module.

There are two things we need to do. Firstly we define a variable through which the object can be referenced. We do this as follows:

Dim objPerson As clsPerson

Here objPerson is the name of the new object, and clsPerson defines the object's type - ie the Class Module on which it is based.

Secondly, we instantiate the object with the New keyword; and link the object to the variable that we created above with the Set keyword. This is done as follows:

Set objPerson = New clsPerson

However, before we can create an instance of the class we must first add our code to the class module. Let's start by writing the code to create the class module properties.

Setting and Getting Class Module Property Values

The person object we are creating has three properties - name, age and gender.  Class properties are basically variables with CLASS MODULE level scope.  As such, they are declared pretty much the same way as variables in the declarations section of the CLASS MODULE, except we use the PRIVATE keyword instead of DIM.  As such, this is the code we need to write:

Private strName As String
Private intAge As Integer
Private strGender As String

By restricting scope to CLASS MODULE level (as opposed to GLOBAL), the data stored in each variable cannot be accessed directly from outside the class module. This means we must set up a special sort of interface within the class module so we may get and set our object property values after the object has been instantiated.  We do this through PROPERTY LET and PROPERTY GET.  These are located in the main section of the class module code with it's SUB's and FUNCTIONS. Here are the blocks of code to set and get the NAME property stored in the strName class module variable.

Property Let Name(strNameIn As String)
   strName = strNameIn
End Property

Property Get Name() As String
   Name = strName
End Property

Let's examine how these work.  Imagine we have created an instance of the clsPerson class and called it objPerson.  To set the Name property of the object to, let's say, "Sarah",  we would use the following code:

objPerson.Name = "Sarah"

Doing this invokes PROPERTY LET NAME in the clsPerson class module code (see code snippet above).  The string value "Sarah" is received as the strNameIn argument, and is then assigned to the strName class module variable that we set up in the declarations section above.  As such,  PROPERTY LET has set the value of a private class module variable from a location external to the class module itself.

Then to retrieve the value of the objects Name property from outside the class module, we just need to reference the object name (eg objPerson) and property (eg Name) in the same way.  For example, to retrieve the property value and store it in a variable called strGetName we would use the following code:

strGetName = objPerson.Name

Doing this invokes PROPERTY GET NAME in the clsPerson class module (see code snippet above).  PROPERTY GET returns a returns the value of the property by assigning a value to NAME.  As such, "Name = strName" assigns the value stored in the strName class module variable to the objects Name property and returns this value whenever the object's Name property is referenced outside of the class module.  It works in a similar way to calling a VBA FUNCTION.

The Age and Gender properties in the clsPerson class are set and retrieved in the same way.  The screenshot below shows all the class module code to set and get the clsPerson properties:

Class module code for clsPerson

Adding SUB's and FUNCTION's to the Class Module

Class modules and objects are not just about storing and retrieving property values.  As written above, we can also process and work with those property values in all kinds of ways.  To do this, we add SUBs and FUNCTIONs to the class module.  These are referred to as class methods, and providing they have been created using the PUBLIC keyword (as opposed to PRIVATE), they can be called from outside the class module after the object has been instantiated.

We are going to create a simple method to categorize a person based on the information stored in the object properties.  When the method is called after instantiation, it will return one of eight categories which describe the person stored in our object.  These are:

  1. Male under 18
  2. Female under 18
  3. Male 18 to 30
  4. Female 18 to 30
  5. Male 31 to 64
  6. Female 31 to 64
  7. Male 65 and over
  8. Female 65 and over
To do this we shall write a  PUBLIC FUNCTION called categorizePerson. Here is the code we shall use:

Public Function categorizePerson()
On Error GoTo myError 
    Dim strAgeCat As String  
    If intAge < 18 Then
        strAgeCat = "under 18"
    ElseIf intAge > 18 And intAge <= 30 Then
        strAgeCat = "18 to 30"
    ElseIf intAge > 30 And intAge <= 65 Then
        strAgeCat = "31 to 64"
    ElseIf intAge >= 65 Then
        strAgeCat = "65 and over"
    End If
    categorizePerson = strGender & " " & strAgeCat  
    Exit Function  
    MsgBox Error$
    Resume leave  
End Function

As we can see, the method uses IF .. THEN .. ELSEIF statements to select an age category based on the value of the age property stored in the intAge class module variable. The person's gender is then added to the description (thereby doubling the number of potential categories) and returned to the calling code.
The code to invoke the method after the object has been instantiated is as follows:


Testing the Custom Module

In order to demonstrate how all this works in practice, I have created an unbound Access form to test our clsPerson class.  The form allows us to enter the three property values used by clsPerson, and create a new instance of the class containing these values when the SET PERSON PROPERTIES control button is clicked.
After clicking SET PERSON PROPERTIES the btnSet_Click event (shown in the screenshot below) is invoked. It's code creates a new object instance called objPerson using the SET and NEW keywords. The values contained in the unbound textboxes are then referenced and set as the respective Name, Age and Gender properties for the object. Note how the objPerson variable is declared in the declarations section of the form module so it will persist as long as the form is still open or its value is reset to NOTHING when the DELETE PERSON button is clicked thereby invoking the btnDeleteObj_Click event.

Once the object has been created, the btnSet button is disabled through the code logic in the setControls sub (see screenshot above). This also enables the other three buttons which let us retrieve the property values, categorize the person, or delete the object.

Clicking the GET PERSON PERSON PROPERTIES button invokes the btnGet_Click event where the property values are retrieved, added to a string variable, and displayed in the OUTPUT textbox (see screenshot below).

Finally, clicking the CATEGORIZE PERSON button invokes code in the btnCat_Click event and the category is displayed in the OUTPUT textbox (see below)

As such, we can see how the properties and methods in clsPerson (ie PROPERTY LET, PROPERTY GET, and CATEGORIZE PERSON) are invoked with statements such as objPerson.categorisePerson after the object has been instantiated in the TEST CUSTOM PERSON OBJECT form.  I hope this gives you a good example of how VBA class modules and custom objects work in practice.

Friday 17 May 2019

Linking Access to an Excel Worksheet

Excel is great for number crunching, and can even be used as a basic database to store information.  However, when it comes to displaying and presenting information, the MS Access database has some big advantages over it's peer in the Office 365 suite of software. The reason for this is that Access has a number of tools and features specifically designed to make data easier to read and understand - the Reports facility being just one.

The good news is that Access has the ability to connect to, and work with, Excel data in two different ways.  Firstly, Access can import data from an Excel worksheet into an Access table.  This method lets us work with a "snapshot" of data from Excel as it was at the time the data was extracted (there is more information about importing from Excel in my post on "Importing and Exporting Data between Access and Excel").  The second method is to set up a "live" link between the Excel worksheet and the Access table. This has the advantage of giving us direct access to current data in the spreadsheet; so any updates, additions or deletions will show up in Access (after data is refreshed/reloaded) as soon as the data is saved in Excel. However, please do note that this connection is read-only; new data cannot be saved back into the Excel spreadsheet without specifically doing an additional export.

Today we are going to learn how to set up this "live" link. To do so, I have set up a sample Excel worksheet with fictitious personnel records.

Linking to Excel
  1. Create a new Access Database, or open an existing one.
  2. Select the EXTERNAL DATA ribbon.
  3. Click the NEW DATA SOURCE icon in the IMPORT AND LINK group.
    External Data Ribbon
    Above: Adding a New Data Source from the External Data ribbon.
  4. Select FROM FILE from the drop-down menu, and then EXCEL from the sub-menu.  This opens the GET EXTERNAL DATA - EXCEL SPREADSHEET dialog form.
    Get External Data - Excel Spreadsheet dialog form
    Above: The Get External Data - Excel Spreadsheet dialog form.
  5. Click the BROWSE button and select the Excel spreadsheet you want to link to.
  6. Click the LINK TO A DATA SOURCE BY CREATING A LINKED TABLE radio button, and then click OK.  
  7. The next page of the wizard opens where you should see a sample of the worksheet you are linking to.  If your worksheet had column headings, ensure the FIRST ROW CONTAINS COLUMN HEADINGS box is ticked, and click NEXT. (Please note that if your spreadsheet has more than one worksheet or named range, you will see an additional wizard page asking you to select the specific worksheet or range before the page in the screenshot below).
    MS Access - Link Spreadsheet Wizard
    Above: First page of the Link Spreadsheet Wizard.
  8. Enter the name you are going to call the linked Access table in the last page of the wizard, and click FINISH.

Once you have done this, you will see the new linked table appear in the left-hand Access navigation pane under TABLES.  Note how the linked table icon is a blue arrow pointing to the Excel logo, thereby indicating the table is linked to an Excel spreadsheet.

MS Access table linked to Excel
Above: The table linked to Excel.

Now the link has been established to the Excel worksheet, we are free to base forms, reports and queries on the linked table as if it is native to Access itself.

Friday 5 April 2019

Using Custom Functions in Calculated Controls

Back in May 2012, I wrote a blog article on Writing Custom Functions for Access VBA.  Custom functions work the same way as MS Access built-in functions such as DateAdd, DatePart and DSum, but are instead created ourselves as database developers.  We do this by creating a public function with the VBA programming language and save it inside a global module within the database.

The blog I wrote in 2012 explained how these custom functions can be accessed from sub procedures associated with forms and reports elsewhere in the database.  Today, however, I am going to explain how custom functions can be utilised in calculated form controls, without needing to invoke them with VBA itself.

Let's begin by looking at the custom function we are going to use.

Custom Function to get Week Commencing
I have created a custom function called getWeekCommencing to calculate the week commencing date of a given week, in a given year.  For example, the week commencing date of the 14th week of 2019 is 1st April 2019 (if we count Monday as the first day of the week). As such the function takes two arguments - week number and year.  The full syntax for using the function is as follows:

getWeekCommencing(weekNumber, Year)

The code I used to create this function is as follows:

Public Function getWeekCommencing(intWeekNo, intYear)
On Error GoTo myError

    Dim intJan1 As Integer
    Dim varStartDate As Variant  
    intJan1 = Weekday(DateSerial(intYear, 1, 1), vbMonday)
    varStartDate = DateAdd("d", -(intJan1 - 1), DateSerial(intYear, 1, 1))
    getWeekCommencing = DateAdd("ww", intWeekNo - 1, varStartDate)  
    Exit Function
    MsgBox Error$
    Resume leave  
End Function

If you are unfamiliar with VBA you can still copy this code into your database and use it within a calculated control. There are instructions for doing this below:

Instructions for adding the function to your database.

  1.  Copy the code above onto your clipboard.
  2.  Open the database you are going to add the function to.
  3.  Select the CREATE ribbon.
    Above: The MODULE icon is located on the right-hand side of the CREATE ribbon.

  4. Click the MODULE icon from the MACROS AND CODE group.  This opens the VBA editor and creates a new module ready for the code to be added:
  5. Paste the code into the VBA editor as in the screenshot below:
Above: The VBA Editor:
You may notice that I have changed the default name of the Module (see the PROJECT EXPLORER in the 
left-hand side bar) from Module 3 to "myFunctions".  You can do the same by highlighting the module name in the 
project explorer and hitting the F4 button to bring up the PROPERTIES window. You may then change the name property
 to one of your choice.  However, this is not essential.
The custom function is now ready to use in a calculated form control. 
Setting up the Test Data for this Exercise

Before we create the form to test the function, we first need to set up a simple database table containing test data. The table needs just two fields: WeekOfYear and Year, both of which are of the NUMBER data type.

Above: tblWeeks in Design View

Above: tblWeeks in Form View with test data entered.

Once the table is set up, we can add our test data as I have done in the screenshot above. Although there are  52 week in the year, the first week may not start on a Monday, so the data entered in WeekOfYear field can be anything between 1 and 53 (so the possibility of a partial first week is offset by Week 53).

The Calculated Control

Now we have added the getWeekCommencing function along with test data to our database, we can create the form containing the calculated control.

Above: The Week Commencing Calculator form in Design View.

To do this we need to create a form bound to the tblWeeks table.  We then need to add three text boxes:  the first text box (txtWeekOfYear) is bound to the WeekOfYear field in tblWeeks, and the second (txtYear) is bound to the Year field.  The third text box (txtWeekCommencing) is unbound.  This is where we are going to add our calculated control which returns the week commencing date (based on the data displayed in the WeekOfYear and Year textboxes).

Here are the instructions for creating the calculated control:

  1. Create the third text box that we are going to use for the calculated control as in the screenshot above. 
  2. Display the PROPERTY SHEET if it is not already visibile.  The PROPERTY SHEET icon is located in the TOOLS group of the DESIGN ribbon.
  3. Select the new text box by clicking on it.
  4. Click the OTHER tab of the PROPERTY SHEET, and change the NAME property to txtWeekCommencing. (I also suggest you change the names of the first textbox to txtWeekOfYear and the second to txtYear by selecting them and changing the NAME properties).
  5. Click the DATA tab on the PROPERTY SHEET (having first selected txtWeekCommencing).  We are now going to enter an expression which uses our getWeekCommencing custom function.  
  6.  Enter the expression below directly into the CONTROL SOURCE property:

The txtWeekNumber parameter references the value in the txtWeekNumber textbox, and the txtYear parameter does the same for the txtYear text box.  

In this exercise, the expression was entered directly into the CONTROL SOURCE
property.  Alternatively, we could have clicked the elipse button at the end of the CONTROL SOURCE
property row to open the EXPRESSION BUILDER.  Using the Expresison Builder is, however, something 
I would need to cover another day, in another post!
And that's it! All you need to do now is save the form and open it in FORM VIEW.  Use the form's navigation buttons to view each record in the tblWeeks table.  The calculated control uses the getWeekCommencing custom function to processes the week number and year data for the current tblWeeks record, and displays the appropriate date.

NB - Just to clarify, the format for the week commencing date in this screenshot is for the UK (ie dd/mm/yyyy). 
The same date using the US format would be 01/07/2019 (mm/dd/yyyy). However, your computer should be set up
to display the date format appropriate for your location automatically.

Saturday 2 March 2019

Converting Minutes to Hours:Minutes in MS Access

There may be occasions when we need to convert the difference between a start time and an end time, and display the result in hours and minutes.  For example, suppose we set up an Access table field to record the time a person starts work (the session_start field) and another to record when s/he finishes (the session_end) field.  Rather than set up a third field to store the total time worked, we can instead calculate this value automatically using a calculated control in an Access form, or a calculated field in an Access query.

Calculated Control
Above: the bottom text box (txtHoursWorked) is a calculated control. 
The CONTROL SOURCE is an expression based on the values contained in the top two text boxes
(bound to the session_start and session_end fields in the undelying table).

However, to do this we must use two expressions to calculate the time difference, and then display the time difference in the hrs:mm format.  So if we enter 20:40 as the session_start, and 22:06 for session_end, we need an expression to calculate the total minutes worked (which in this case is 86 minutes), and then convert the total minutes to hours/minutes format (which would be 01:26).  To achieve this we use the DateDiff and FormatDateTime functions.  Lets take a look at each function individually before combing them to produce the required result.

The syntax for the DateDiff function is as follows:

DateDiff("interval", time_1, time_2)

The function works by calculating the time difference between the time_1 and time_2 parameters, and returns the result in accordance with the interval parameter.  In our case, we want need the result returned as minutes, so enter "n" as interval.   Time_1 and Time_2 correspond to the start time and end time.  To get these values for the expression, we can we put a reference to the values contained in the text boxes for "Start time" and "End time".  In our example these text boxes are called txtStartTime and txtEndTime.  This what our DateDiff function looks once we add the parameter values:

DateDiff("n", txtStartTime, txtEndTime)

The value returned in our example is 86 minutes.

The second function that we are going to use is FormatDateTime which converts the value returned by the DateDiff function into hours and minutes.  The syntax we need to use in the FormatDateTime is as follows:

FormatDateTime( (minutes/(24*60) , named_format)

This first parameter is a division of the number of minutes (returned in the DiffFunction) by the total number of minutes in a day -  which in our example is 86/(24*60) - and returns the result in accordance with the value contained in the named_format parameter.  The latter is a numeric value indicating the required time format - which in our example is vbShortTime ie hours:minutes.  The numeric value we enter for the vbShortTime format is 4.  This is what our FormatDateTime function looks like once we add the parameter values:

FormatDateTime((86/(24*60) , 4)

The value returned from this expression is 01:26 - ie 1 hour and 26 minutes.

When we come to enter the actual expression used as the control source for the TOTAL (HRS:MINS) text box (referred to as txtHoursWorked in the screenshot below), we need to combine these two functions by nesting the DateDiff function inside the first parameter of the FormatDateTime function. This is done as follows:

FormatDateTime((DateDiff("n", txtStartTime, txtEndTime/(24*60) , 4)

Finally, we just need to enter this expression into the CONTROL SOURCE property of the
txtHoursWorked text box (see screen shot below):

The txtHoursWorked text box is highlighted on the left, and the expression used as the CONTROL SOURCE property value is highlighted on the right.

Friday 15 February 2019

Creating a Custom Save Button for an MS Access Form.

When we use an MS Access form to create a new record, or update one that already exists, the process of saving that data is normally taken care of automatically "behind the scenes."  All we need to do is move to or create a new record, close the form, or close the database, and Access saves the original record for us.

Record Navigation Buttons: when a record is added or changed, moving to a new or different record 
via the navigation buttons, will save the origin form record automatically.

However, there are times when it may necessary to save a record manually.  Suppose, for example, we have two tables joined together in a one to many relationship. We create a new record on a form bound to a table on the one side of the relationship, and then click a button to open a new form bound to a table on the many side of the relationship.  The newly opened form is then used to create a sub-record for the parent record on the original form.

Parent and sub-forms: In this screenshot, the parent form "Work Session" is bound to the tbl_work_session table, and the "Entry Log" form is bound to the tbl_entry_log table.  There is a one to many relationship between the two tables, with tbl_work_session being on the one side of the relationship.
The problem in this scenario is that when we come to close the form for the sub-record (thereby saving the data to the underlying table on the many side of the relationship), the parent record on the original form has not, at this stage, been inserted into the underlying table on the one side of the relationship.  That is to say, Access has not got around to autosaving the parent record since the parent form has not moved to any other record, or been closed etc - all we have done is click a command button to open a new form.  As such we get an error message saying "You cannot add or change a record because a related record is required in [the parent] table"; this is because the rules of referential integrity have been broken (ie the sub-record in the many table requires a parent record in the one table).

However, it is simple to overcome this issue. We just need to save the parent record manually before trying to close the sub-record form.  A quick and easy way to do this is to click the pencil symbol on the top left of the parent-form, or the SAVE icon in the RECORDS group of the HOME ribbon. This will save the parent record, thereby allowing it's sub-record to be saved afterwards.

 The pencil symbol (above left) can be used to save the current record manually.  Alternatively, the SAVE icon in the RECORDS group of the HOME ribbon (above right) can also be used.
However, this is not particularly useful from the perspective of user-friendliness. That is to say, a user may not realise or understand that this action is necessary.  A better way of doing it would be to save the parent record automatically when the user clicks the command button to open the sub record form. As such, we need to alter the open form button (referred to as "CREATE NEW ENTRY" in our example above) so it also becomes a custom save button.  To do this, we just add the following line of VBA code to the buttons ON CLICK event:

Application.RunCommand acCmdSaveRecord

See the screenshot below for the full code:

VBA code to save the parent record before opening the sub-record form.

Creating a Custom Save Button from Scratch - A Tutorial

Here is a step by step tutorial for creating a custom save button from scratch on Access for Office 365:
  1. Open the form in DESIGN VIEW.
  2. Go to the CONTROLS group of the CREATE ribbon.
  3. Click the MORE button () to the lower right of the control icons, and de-select the USE CONTROL WIZARDS icon when the additional options appear. 
    Above: additonal  options below control icons.
  4. Click the BUTTON control icon () from the CONTROLS ribbon. The cursor will now change to a button icon when it enters the design grid.
  5. Position the cursor at the desired location on the design grid, and click the left hand mouse button.  This will create the new button at the selected location.
  6. Select the new BUTTON contol by left clicking it, and open the PROPERTIES sheet from the TOOLS group of the DESIGN ribbon (if it is not already open).
  7. Click the EVENTS tab on the properties sheet, and left click the ON CLICK row of the events tab.
  8. Click the ELIPSE button (three horizontal dots) which appears on the right hand side of the row.
    Above: the ON CLICK event row on the PROPERTIES sheet.
  9. Select CODE BUILDER from the CHOOSE BUILDER dialog form which opens.  This opens the VBA editor.
  10. Enter the following code in the CLICK sub procedure for the control button.

Above: The CLICK sub procedure for the new control button shown in the VBA editor.
Now when the user clicks the new button at runtime, any data s/he entered will be saved to the corresponding record in the forms underlying table.

Friday 25 January 2019

Passing Multiple Values via the OpenArgs Parameter of DoCmd.OpenForm

The DoCmd.OpenForm command is a useful tool for the Access for Office 365 database developer wanting to control the manner in which a form opens during runtime.  I have written about it previously in my post on how to "Control Form Opening".  However, in today's post, we are going to focus on a specific area of this command's use - that is, how we can pass multiple values via its OpenArgs property.

The OpenArgs parameter of DoCmd.OpenForm gives us the means to pass a single string value to the OpenArgs property of new form being opened.  After the form has opened, this value can then be read and used by any code able to reference the new forms OpenArgs property. As things stand, the limitation of this is that we can only pass one string value as the command executes.  So let's see how we can get around this, and pass any number of strings values in one go.

To demonstrate how this works, I have created an Access for Office 365 form containing three text boxes and a submit button.  When the user populates the text boxes and clicks SUBMIT during runtime, the values contained in each of the three text boxes are passed over to a new form by means of the OpenArgs parameter of the DoCmd.OpenForm command.

Above: Form to pass multiple values via the OpenArgs parameter of DoCmd.OpenForm.

You can download the full OpenArgsPost.accdb database used in the this exercise from here. 

(NB I have tested the download process using the Chrome browser which works OK.  The download process may fail using other browsers such as Microsoft Edge. If you experience issues please try using a different browser). 

Part One: Passing the Values

Let's look at what happens behind the scenes when the SUBMIT button is clicked.  First of all, clicking SUBMIT (referred to as btnSubmit in DESIGN VIEW) results in the control button's ON CLICK event firing.  This, in turn, starts the following VBA event procedure (see screenshot below):

Above: The VBA event procedure for btnSubmit.

The code begins by declaring a string variable called strOpenArgs:

Dim strOpenArgs AS String

The next two lines of code reference the value entered by the user in the first text box.  The value is stored in the strOpenArgs string:

strOpenArgs = txtValue1.Text

The next two lines of code after that reference the value of the second text box, and append it to the strOpenArgs string preceded by a semi-colon (the significance of the semi-colon will be explained in part 3 of this post):

strOpenArgs = strOpenArgs + ";" + txtValue2.Text

This is then repeated for the third text box:

strOpenArgs = strOpenArgs + ";" + txtValue3.Text

So at this point in the program flow, the value of strOpenArgs is as follows:


This is the final value of the DoCmd.OpenForm OpenArgs parameter which will be passed to the new form in the following line of code:

DoCmd.OpenForm "frmReceiveOpenArgs", , , , , , strOpenArgs

Part Two: Retrieving the Values

Let's take a look at the new form which opens after the SUBMIT button has been clicked, and the event procedure explained above has finished executing:

Above: the new form which opens in response to clicking the SUBMIT button.

As you can see in the screenshot above, the new form consists of three empty text boxes (for displaying retrieved values) and a RETRIEVE button.  When the user clicks RETRIEVE the text boxes will be populated with the values submitted from the first form.  In our case, Retrieved Value 1 will display the value "one", Retrieved Value 2 will display the value "two", and Retrieved Value 3 will display the value "three".

Let's look at what happens behind the scenes after the RETRIEVE button is clicked.  Like the first form, clicking the command button, which in this form is called btnRetrieve, results in it's ON CLICK event firing.  This starts the following VBA event procedure (see screenshot below):

Above: The VBA event procedure for btnRetrieve.

The code begins by declaring a string variable called strOpenArgs before referencing the forms OpenArgs property and storing its value in the string.  (Just to recap, the value of the OpenArgs property (ie "one;two;three") was determined by the OpenArgs parameter of the  DoCmd.OpenForm command invoked when the user clicked the SUBMIT button on the previous form):

dim strOpenArgs As String
strOpenArgs = Me.OpenArgs

The next couple of lines of code are very important. A string array called strValues is declared and has its elements populated with data returned from a function called getOpenArgsArray.  This function is located in a separate module called Utilities which is global in scope.  This is where the core of the processing is done for this exercise:

Dim strValues() As String
strValues = getOpenArgsArray(strOpenArgs)

The purpose of the getOpenArgsArray is to split the value of its parameter, strOpenArgs (which in our case is "one;two;three"), into three separate strings, with each array element containing an individual string.  So for us, the strValues array is populated with the following values:

Array ElementValue

These values are assigned to each of the three text boxes in the next six lines of code:

Me!txtRetValue1.Text = strValues(0)

Me!txtRetValue2.Text = strValues(1)

Me!txtRetValue3.Text = strValues(2)

The end result can be seen in the screenshot below:

Above: the end result after the user clicks RETRIEVE.

In this way, we have used the DoCmd.OpenForm OpenArgs parameter to pass multiple values to a new form, thereby overcoming the limitation of only being able to pass a single string within the statement.

Part Three: The getOpenArgsArray Function

However, this post would not be complete without an explanation of the getOpenArgsArray function, as this is where the core of the processing was done for this exercise.  Let's take a look at the code used in the getOpenArgsArray function:

Above: code for the getOpenArgsArray function.
NB: in this screenshot the strArgs array is declared with 7 elements.
This is because the function is global in scope and other event procedures using
 the function may need addtional elements.  This means that the OpenArgs
 parameter of DoCmd.OpenForm can pass up to 7 values with this current setup.
If more elements are needed, the array can be declared with an adjusted number as necessary.

As mentioned in section 2 above, the purpose of the getOpenArgsArray function is to split the value of the strOpenArgs parameter passed to the function, into individual sections, and to save each section as a separate array element. So in our case, the function receives a string containing the value "one;two;three", and returns an array with three elements ie 

Array Element    
Element 1 
Element 2
Element 3

This is acheived by iterating through the strOpenArgs string in a FOR NEXT loop and appending each individual character to a temporary string called strBuildString.  Then when the current character of strOpenArgs in the loop is one of the semi-colons, the value of strBuildString is saved to a new array element. 

Lets break this down further.

The following three lines of code are concerned with iterating through each  character contained in the strOpenArgs string.  Each character is temporarily stored in a string variable called strChr:

For i = 1 To Len(strOpenArgs)
    Dim strChr As String
    strChr = Mid(strOpenArgs, i, 1)

The value of strChr is then checked to see whether or not it is a semi-colon.  If it is NOT a semi-colon, the character is appended to the strBuildString variable :

    If Not strChr = ";" Then
          strBuildString = strBuildString + strChr

If, on the other hand, the character IS a semi-colon, the current value of strBuildString is saved as a  new array element in strArgs().  The strBuildString variable is then cleared ready to build the value of the next array element:

             strArgs(argCounter) = strBuildString

             strBuildString = ""

The element number of the array is kept track of in an integer variable called argCounter.  This is incremented by one after the strBuildString variable is cleared:

              argCounter = argCounter + 1
     End If

Next i

After the last iteration of strOpenArgs has completed, the final array element is saved, and the return value of the getOpenArgsArray function is set to the value of the strArgs() array:

strArgs(argCounter) = strBuildString
getOpenArgsArray = strArgs

Exit Function