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Certain controls cause a validating event to fire when they are exited For example, as a user moves from text box to text box on a form, the validating event can be used to ensure that the user has entered correct data We have added an extra text box to our Students tab page (see Figure 19-12) A shortcut, when using the Visual Designer, to register a new event with a handler is to click the lightning bolt (for events) in the Properties Explorer PART IV

Figure 19-12

A list of that control s events is presented (see Figure 19-12) and by double-clicking on the event, the code is added to your program We double-clicked on the Validating event, and the Visual Designer added the following code:

Security personnel should have access to a current list (including a list of the residents telephone numbers) of key individuals and organizations that would be involved in the activation of a disaster plan This list should include: A Corporation department heads B All employees C Police and fire departments D A and C above

thistextBox1Validating += new SystemComponentModelCancelEventHandler ( thistextBox1_Validating);

Mixed Numbers and Fractions To convert between mixed numbers and fractions, multiply the denominator of the fraction by the integer and add the numerator a A ratio is a fraction but written as a:b where a and b are numbers and b 0 b a c = A proportion is an equation that relates two ratios a:b = c:d or b d Decimals A decimal is a means of expressing the numerical value of a fraction Consider, for example, the decimal number 321524 Position 321524 321524 321524 321524 321524 Tens Ones Tenths Hundredths Thousandths Value of Position 10 1 01 001 0001 Value of Decimal Number 30 2 1 10 5 100 2 1000 4 10000 30 2 01 005 0002

A Validating event method is also added to the code:

private void textBox1_Validating (object sender, SystemComponentModelCancelEventArgs e) { // place your validation code here }

217 There are two types of terrorist groups: left-wing terrorist groups and right-wing terrorist groups A True B False

Inside the method, you can add code that will test the value entered by the user and set the Cancel property of the CancelEventArgs object to True if the data is not valid This has the effect of eliminating the tab or click to the next control and gives you an opportunity to present an error message to the user The user will then have to correct the data and try to move off the control again Validation will continue to happen until your method is successfully completed Here is an example of validation code:

{ if ( // validation test here) { eCancel = true; MessageBoxShow ("Invalid data!"); } }

EXAM TIP You can set the CausesValidation property of a control to False if you do not want the Validation event to fire when exiting the control

On what date did the United States encounter the first incident of modern-day left-wing terrorism A 1953 B 1973 C 1905 D 1961

The ErrorProvider control lets you display an error message if the information entered by the user is in error By using the ErrorProvider, you can set an icon next to the control that contains the data in error This is more desirable than using a message box, because as soon as the user dismisses the message box, they no longer have a record of the error A message created with the ErrorProvider stays on the form until the correction to the data is made Figure 19-13 demonstrates our validation of the first text box Notice the big question mark beside the text box The ErrorProvider has placed it there TIP Move your mouse over the question mark to see the error message

Figure 19-13

Since 1961, approximately how many major terrorism events have occurred around the world A 60 B 50 C 150 D 300

Summary