On Error Visual Basic Excel
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three flavors: compiler errors such as undeclared variables that prevent your code from compiling; user data entry error such as a user entering a negative value where excel vba try catch only a positive number is acceptable; and run time errors, that occur
Vba Error Handling Best Practices
when VBA cannot correctly execute a program statement. We will concern ourselves here only with run time errors. Typical
On Error Goto Line
run time errors include attempting to access a non-existent worksheet or workbook, or attempting to divide by zero. The example code in this article will use the division by zero error (Error
Vba On Error Exit Sub
11) when we want to deliberately raise an error. Your application should make as many checks as possible during initialization to ensure that run time errors do not occur later. In Excel, this includes ensuring that required workbooks and worksheets are present and that required names are defined. The more checking you do before the real work of your application begins, the more vba error handling in loop stable your application will be. It is far better to detect potential error situations when your application starts up before data is change than to wait until later to encounter an error situation. If you have no error handling code and a run time error occurs, VBA will display its standard run time error dialog box. While this may be acceptable, even desirable, in a development environment, it is not acceptable to the end user in a production environment. The goal of well designed error handling code is to anticipate potential errors, and correct them at run time or to terminate code execution in a controlled, graceful method. Your goal should be to prevent unhandled errors from arising. A note on terminology: Throughout this article, the term procedure should be taken to mean a Sub, Function, or Property procedure, and the term exit statement should be taken to mean Exit Sub, Exit Function, or Exit Property. The term end statement should be taken to mean End Sub , End Function, End Property, or just End. The On Error Statement The heart of error handling in
the wrong time. The application may crash. A calculation may produce unexpected results, etc. You can predict some of these effects and take vba on error goto 0 appropriate actions. Some other problems are not under your control. Fortunately, both Microsoft err.number vba Excel and the VBA language provide various tools or means of dealing with errors. Practical Learning:Introducing Error Handling Open vba on error msgbox the Georgetown Dry Cleaning Services1 spreadsheet and click the Employees tab Click the Payroll tab Click the TimeSheet tab To save the workbook and prepare it for code, press F12 http://www.cpearson.com/excel/errorhandling.htm Specify the folder as (My) Documents In the Save As Type combo box, select Excel Macro-Enabled Workbook Click Save Introduction to Handling Errors To deal with errors in your code, the Visual Basic language provides various techniques. One way you can do this is to prepare your code for errors. When an error occurs, you would present a message to the user to make http://www.functionx.com/vbaexcel/Lesson26.htm him/her aware of the issue (the error). To prepare a message, you create a section of code in the procedure where the error would occur. To start that section, you create a label. Here is an example: Private Sub cmdCalculate_Click() ThereWasBadCalculation: End Sub After (under) the label, you can specify your message. Most of the time, you formulate the message using a message box. Here is an example: Private Sub cmdCalculate_Click() ThereWasBadCalculation: MsgBox "There was a problem when performing the calculation" End Sub If you simply create a label and its message like this, its section would always execute: Private Sub cmdCalculate_Click() Dim HourlySalary As Double, WeeklyTime As Double Dim WeeklySalary As Double ' One of these two lines could produce an error, such as ' if the user types an invalid number HourlySalary = CDbl(txtHourlySalary) WeeklyTime = CDbl(txtWeeklyTime) ' If there was an error, the flow would jump to the label WeeklySalary = HourlySalary * WeeklyTime txtWeeklySalary = FormatNumber(WeeklySalary) ThereWasBadCalculation: MsgBox "There was a problem when performing the calculation" End Sub To avoid this, you should find a way to interrupt the flow of the program be
execution at a specified line upon hitting an error. Situation: Both programs calculate the square root of numbers. Square Root 1 Add the http://www.excel-easy.com/vba/examples/error-handling.html following code lines to the 'Square Root 1' command button. 1. First, we declare two Range objects. We call the Range objects rng and cell. Dim rng As Range, cell As Range 2. We initialize the Range object rng with the selected range. Set rng = Selection 3. We want to calculate the square root of each cell in a randomly selected on error range (this range can be of any size). In Excel VBA, you can use the For Each Next loop for this. Add the following code lines: For Each cell In rng Next cell Note: rng and cell are randomly chosen here, you can use any names. Remember to refer to these names in the rest of your code. 4. Add the following vba on error code line to the loop. On Error Resume Next 5. Next, we calculate the square root of a value. In Excel VBA, we can use the Sqr function for this. Add the following code line to the loop. cell.Value = Sqr(cell.Value) 6. Exit the Visual Basic Editor and test the program. Result: Conclusion: Excel VBA has ignored cells containing invalid values such as negative numbers and text. Without using the 'On Error Resume Next' statement you would get two errors. Be careful to only use the 'On Error Resume Next' statement when you are sure ignoring errors is OK. Square Root 2 Add the following code lines to the 'Square Root 2' command button. 1. The same program as Square Root 1 but replace 'On Error Resume Next' with: On Error GoTo InvalidValue: Note: InvalidValue is randomly chosen here, you can use any name. Remember to refer to this name in the rest of your code. 2. Outside the For Each Next loop, first add the following code line: Exit Sub Without this line, the rest of the code (error code) will be execut