lecture set 8

Lecture Set 8

Validating Data and Handling Exceptions

Part C – Exception Handling with Other VB Tools

Slide 2

Objectives

To understand how to us some additional VB tools in handling exceptions Masked textboxes Check boxes Scrolling tools later to be used with List

Boxes and Combo Boxes

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Slide 3

Using Masked textboxes

Similar to what you can do with a typical database tool

Forces user entries to comply with a specific format User can’t leave the control until a valid

entry has been made (valid in terms of the mask)

Masks are best used with things like dates, phone numbers, zip codes and the like

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Slide 4

Two Useful Properties of Mask Boxes

The Mask Property – You set the mask you want to force the

format for a given text box This then becomes a type validation

mechanism that you do not have to code The ValidatingType Property –

The code generated for this control allows you to set this property to a data type such as Date or Decimal to even further restrict what the user is allowed to enter

But YOU have to set the property by writing code to do so

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Slide 5

You may STILL need to do more work …

You can do this by coding the TypeValidationComplete Handler for the control -- -- --

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Slide 6

The Invoice Total form with two masked text boxes

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Slide 7

Typical masks used in the Mask property of a masked text box

Mask property Mask when run Example Entry requirements

L _ C One letter

####.## ____.__ 0450.50 Six digits with two decimal places

00/00/0000 __/__/____ 06/08/2007 Six digits in date format

(999) 000-0000 (___) ___-____ 555-432-3291 Ten digits in phone number format

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Slide 8

Code that sets the ValidatingType property for a masked text box (optional)

mskSubtotal.ValidatingType = GetType(System.Decimal);

Note If you set the ValidatingType property for the control, the entry is

tested to see whether it’s valid for that type. Then, you can use the TypeValidationCompleted event for further testing.

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Slide 9

An event handler for the control’s TypeValidationCompleted event (VB) (optional) Private Sub mskSubtotal_TypeValidationCompleted( _ ByVal sender As System.Object, _ ByVal e As _ System.Windows.Forms.TypeValidationEventArgs) _ Handles mskSubtotal.TypeValidationCompleted If e.IsValidInput Then If CDec(mskSubtotal.Text) <= 0 Then MessageBox.Show( _ "Please enter a subtotal " _ & "that's greater than zero.", _ "Entry Error") e.Cancel = True End If Else e.Cancel = True End If End Sub

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Slide 10

Murach’s Visual Basic 2005, C7

Two problems with using event handlers for Validating events (optional)

Validating event handlers are only triggered if the user moves the focus to the control.

There isn’t any way for the user to cancel an entry once the entry is started.

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Slide 11

Are Textboxes a Pain in the Rear?

Validating input is painful in general, and it is even more so when you give the user free reign with regard to data entry (as we do when we use textboxes)

So what do we do? Start thinking about other controls

which the user can use to avoid typing entries

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Slide 12

Controls that Rely on Decision-Making

Three controls are commonly used with decision-making The CheckBox control allows the end user

to select one of two possible values The HScrollBar control and VScrollBar

controls allow the user to select a value from a range of values

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Slide 13

The CheckBox Control

The CheckBox control allows the end user to select from two possible values

The CheckAlign property defines where the check box appears

The Boolean Checked property indicates whether the box is checked

The Text property contains the visible text The TextAlign property controls the

alignment of the text The CheckedChanged event fires when the

value of the Checked property changes

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Slide 14

The CheckBox Control (Example)

Determine whether the CheckBox named chkDemo is checked

if (chkDemo.Checked == true) txtState.Text = "Checked“;else txtState.Text = "Not checked“;

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Slide 15

The HScrollBar and VScrollBar Controls (Introduction)

Use to select a value from a range of values

The two scroll bars work the same way The HScrollBar has a horizontal

orientation The VScrollBar has a vertical orientation

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Slide 16

The HScrollBar and VScrollBar Controls (Syntax)

The Minimum and Maximum properties define the range of values

The current value is stored in the Value property

The SmallChange and LargeChange properties define the magnitude of change

The Scroll event fires while scrolling The ValueChanged event fires when

scrolling is complete and the value changes

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Slide 17

Changing the Value Property of a Vertical Scroll Bar

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Slide 18

The Maximum and Minimum Properties of a Vertical Scroll Bar

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Slide 19

Scroll Event (Example)

Display scroll bar values

private void vsbDemo_Scroll( _ object sender, _

System.Windows.Forms.ScrollEventArgs e) { txtValue.Text = vsbDemo.Value.ToString; txtOldValue.Text = e.OldValue.ToString; txtNewValue.Text = e.NewValue.ToString;} // end vsbDemo

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