Validating windows forms

A control's intention to support validation is indicated by setting its Causes Validation property to True, the default value for all controls.

When a control's Causes Validation property is set to True, its Validating event is fired if focus shifts to another control that also has a Causes Validation value of True.

It is possible that one or more controls have not had the focus before OK is clicked and, consequently, have not fired their Validating events.

Form-wide validation is implemented by manually calling the validation logic tied up in each Validating event, achieved by enumerating all controls on a form, setting focus to each, and calling the form's Validate method, like so: The Cancel button, however, does not need to implement form-wide validation because its job is to simply close the form.

Consequently, you handle Validating to implement your validation logic, such as ensuring Name is provided: Validating supplies a Cancel Event Args parameter that lets you signal whether the field was valid by setting its Cancel property.

If Cancel is True (invalid field), focus remains on the invalid control. Windows Forms validation process The onus is on you to visually inform the user of valid or invalid data, and instinct might suggest the status bar as an appropriate mechanism for doing so.

Thus, a programmatic experience is transformed into a declarative experience where declarative is synonymous with productive. The next step is to work out what sort of validators we'll need. I'm a big consistency fan and also have "don't reinvent the wheel" tattooed across my forehead (backwards, of course, so I can see it in the mirror when I brush my teeth).The story begins with Jerry arriving at Karen's apartment.After a few moments of friendly banter, Karen rather unusually asks Jerry for two forms of identification—a major credit card and valid driver's license.Michael Weinhardt 16, 2004 Summary: Data validation is a key step in ensuring clean data capture and subsequent processing and reporting.This installment explores the programmatic validation infrastructure native to Windows Forms and builds upon that foundation to develop a custom library of validation components designed to provide a more productive validation experience akin to using ASP. (24 printed pages) Download the winforms03162004_sample file.

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This turns out to be an ideal situation for Windows Forms validation. A good place to start is to see what validators ASP. As such, I think the main goal should be to create Windows Forms validators that are consistent with their ASP.

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