This is continuation to my previous article Data Validation Controls in ASP.NET 2.0 Part 1
Validation Controls
RequiredFieldValidator Control: The RequiredFieldValidator control is used to ensure that fields that must be populated with data are, indeed, populated with data. This control can be used with virtually any data entry controls, such as TextBox, DropDownList, and CheckBox. The RequiredFieldValidator control works by comparing the selected value of the control specified in the ControlToValidate property against an initial value that you specify. If you do not specify an initial value, an empty string is assumed.
This initial value against which comparisons are made is established using the InitialValue property. The default value is an empty string. However, you can set it to any value you like. Suppose, for example, you want to provide some assistance to users specifying dates by pre-filling the date field with MM/DD/YYYY. In this situation, you can set the InitialValue property of the associated RequiredFieldValidator control. This means that the user is still required to specify a value and cannot rely on the initial default value that you provide for guidance.
RangeValidator Control: Situations in which a value must fall within a certain range, rather than merely being specified, call for the RangeValidator control. This control allows you to ensure that a specified value is within acceptable limits, using a combination of properties including MaximumValue and MinimumValue. If either of these properties is blank, the control assumes no maximum or minimum (depending on which is blank).
The RangeValidator control allows you to validate the ranges of various data types. You are not restricted to numeric types. In fact, the RangeValidator control supports range validation of any data type described by the ValidationDataType enumeration. These include Currency, Date, Double, Integer, and String.
RegularExpressionValidator Control: Regular expressions are an extremely powerful means of quickly parsing text. Regular expressions use an extensive pattern-matching notation to provide searching, replacing, and other text operations quickly and efficiently. The pattern-matching capabilities of regular expressions are of particular interest when using the RegularExpressionValidator control.
Regular-expression validation is generally used to ensure that specified data matches a predetermined pattern. For example, all e-mail addresses follow a common pattern. The regular expression used for comparison is specified with the ValidationExpression property. This property can contain any valid regular expression. Relying once again on the example of validating an e-mail address, you can use the following regular expression.
\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*
It is pretty obvious that the regular expression syntax is quite cryptic. Fortunately, there are libraries of regular expressions available. In fact, the RegularExpressionValidator control has some predefined regular expressions (including e-mail address). You can always, of course, write your own regular expressions for validation. Suppose, for example, you have a custom purchase order number format. You can use a regular expression to validate data in the purchase order number field against the pattern you define.
CompareValidator Control: Sometimes you need to compare the value in one field to that of another field instead of to some preset value, range, or pattern. In these situations, you can use the CompareValidator control. Like other validation controls, this control uses a ControlToValidate property. In addition, it adds a ControlToCompare property. This property gives you the ability to specify another control against which the value of the control in the ControlToValidate property is compared.
If you want to compare the control's value against a constant value, you can use the ValueToCompare property instead of the ControlToCompare property. If you set both properties, the ControlToCompare property takes precedence over the ValueToCompare property.
The default comparison operator for the CompareValidator control is equality. However, this is programmable through the Operator property. Valid operators are defined by the ValidationCompareOperator enumeration and include Equal, NotEqual, GreaterThan, GreaterThanEqual, LessThan, LessThanEqual, and DataTypeCheck. The DataTypeCheck operator is the only unary operator among them. It is used to determine whether the data in the control identified by the ControlToValidate property is of a certain type. In fact, if you set the ControlToCompare and ValueToCompare properties, they are ignored if the operator type is set to DataTypeCheck. The DataTypeCheck operator uses the value of the Type property as a base for determining the acceptable data type. The Type property is set based on the ValidationDataType enumeration as described in the RangeValidator control previously mentioned.
CustomValidator Control: The controls described up to this point generally focuses on validating one or two fields based on specific, bounded parameters. Typical requirements, however, usually fall outside the capabilities of the intrinsic controls. In anticipation of this, the creators of ASP.NET made the CustomValidator control. The CustomValidator control provides you with an opportunity to create custom validation logic for situations requiring complex business rules validation.
Like other validation controls, the CustomValidator control exposes common properties such as ControlToValidate, Display, ErrorMessage, Text, and ValidationGroup. Also like other validation controls, the CustomValidator control supports both server-side and client-side validation. To associate custom server logic with the control, you must override the ServerValidate event. One of the parameters of the event handler for this event is an object of type ServerValidateEventArgs. Based on the results of the custom validation logic, you can set the IsValid property of the ServerValidateEventArgs object. For client-side validation, you must create a JavaScript function and reference that function using the ClientValidationFunction property of the CustomValidator control.
ValidationSummary Control: In addition to identifying specific fields with data entry problems, it is often useful to provide users with a summary of validation problems on a form. You can use the ValidationSummary control to provide that summary information to users. The ValidationSummary control is used to display the ErrorMessage property values from validation controls on the page when controls being validated are invalid.
Using the ValidationSummary control can improve usability by minimizing distracting and confusing text and by drawing the user's attention to a single location. Displaying specific data validation problems next to each field can consume a lot of screen real estate. In addition, it can cause shifts in screen layout, which leads to confusion. Using a ValidationSummary control concentrates more verbose information in a single location. Good examples of this include placing asterisks or exclamation points next to fields with validation problems.
Validation control grouping has many advantages. First, it improves performance by instructing ASP.NET to perform validation on controls associated with a particular group. To accomplish this, ASP.NET 2.0 adds a ValidationGroup property to other controls that can cause postbacks such as buttons. This means that you can associate a Save button with a particular validation group. The Page class's Validate method is overloaded to accept a validation group name as an input parameter. When all of this is connected, the button instructs the page to perform server-side validation on only those controls in the specified group.
Another advantage of validation control is that it affords you the ability to restrict the information that is presented in a ValidationSummary control. Clearing the ValidationGroup property of the ValidationSummary control effectively associates the summary control with validation controls that also have a non-specified ValidationGroup property. Alternatively, specifying a value for the ValidationGroup property associates the ValidationSummary control with validation controls in the same group.
Summary
CompareValidator: Compares a user value against a constant, another control, or a specific datatype.
CustomValidator: Verifies a user entry against custom code written by a developer. (Values can be derived at run time.)
RangeValidator: Verifies that a user entry is between an upper and a lower bound, using numbers, alphabetic characters, and dates.
RegularExpressionValidator: Verifies that a user entry matches a pattern defined by a regular expression such as e-mail address or telephone number.
RequiredFieldValidator: Verifies that a user enters a value.
|
No responses found. Be the first to respond and make money from revenue sharing program.
|