MForm validation

Validating the Root control

The MForm controls use the ASP.NET validation scheme.

There is a separate validator control for the Root control, it is called the RootValidator. This validator inherits from the ASP.NET BaseValidator class.

All the properties available to standard .NET validators are also available in the RootValidator. These are:

ControlToValidate - the ID of the Root control, that the validator is attached to.
ValidationGroup - a named group of common validators
Text - a static text displayed on error
Display - a display type: None, Static or Dynamic

If the error should be displayed somewhere else, the .NET ValidationSummary control may be used.

The RootValidator must be placed inside the same naming container as the Root control. It is illegal to add the RootValidator inside the contents of the Root control.

The MForm inner validation process

The RootValidator control coordinates the validation of the controls tree inside the Root control, both on the client and on the server side.

Each of the MForm item controls may contain a Constraint object inside the Additions property. The Constraint property must implement the IsValid method, that takes the item as the parameter - this way the validation is perforemed on server side. Each class inheriting form the Constraint also adds a client script resource to the page. When the MForm item is loaded on the client side, it has all the constraints registered - and they are checked on item values change - this way the validation is performed on the client side.

The validation on the server side traverses recursively all the child controls that implement the IXmlValidatingEditor interface. If you want to extend the MForm tree with custom controls that take part in the validation process, implement the IXmlValidatingEditor interface in your control.

For existing MForm item constraints look in the Constraints chapter.

Data type validation

In order to reduce verbosity of the MForm controls tree, one constraint does not need to be added to every leaf definition.

This constraint is called the DataTypeConstraint and it checks if the data inside the leaf item matches the data type of the item.

The data type constraint, like some of the built-in constraint, has some predefined error messages defined. These error messages are in the MForm resource files. To change the default error message, the data type constraint needs to be added explicitly to the item additions, and needs to have the ErrorText property set.

The error messages

Every constraint has an ErrorText property. This property is a description of the error in case of a situation when the constraint is not met.

When MForm is validated, it stops for the first constraint that is not matched. The displayed error text concerns the item that is the owner of the constraint.

By default, the error message will only be shown on button pressing and will display only the data about the errorneous field.

For a solution to add error messages near the fields, check the Error label example page