Within ASP.NET, data is most often input through textbox
controls, although this varies based upon the need. A Textbox is used to input
names, numbers, dates, and inputs of other types. With the AJAX control
toolkit, it is easy to restrict the type of input into the textbox.
When trying to extract the values from the textboxes and
converting them to their correct data type, there are some challenges you have
to be aware of. For instance, with a DateTime data type, the input has to be
checked to ensure it is correct. If the user enters the following values: 13/13/2008,
1/113/2008, 4/32/2008, when these values are passed to DateTime.Parse or
Convert.ToDateTime, an exception will be thrown.
It is better to use DateTime.TryParse instead to get to the
date's value. TryParse returns back an empty value, and returns false if the
value is invalid. The same concept applies to numerical values; TryParse, at
least, fails gracefully. Failing gracefully is a good safeguard to prevent an
error.
Ideally, it is best to restrict or prevent the invalid input
in the first place. The AJAX control toolkit contains control extenders that
restrict the input into it. For instance, the masked edit extender can restrict
the input to fit money, date, and numerical input.
Listing 7
<ajax:MaskedEditExtender id="ext" runat="server" Mask="99/99/9999" MaskType="Date" />
As an alternative, the filtered textbox extender restricts
the type of characters that can be entered into it. It can control input to be
only numbers, only lowercase letters, uppercase letters, custom letters, or any
combination. Below filters out numbers, but allows a decimal point.
Listing 8
<ajax:FilteredTextBoxExtender id="ext" runat="server"
FilterType="Numbers,Custom" ValidChars="." />
Make sure you use of the validation controls as well. Validation
controls restrict invalid input being entered. For instance, even though the
FilteredTextBoxExtender filters out values other than numbers or decimals, it
will allow more than one decimal point. The regular expression validator below
will prevent that.
Listing 9
<asp:RegularExpressionValidator id="rev" runat="server" ControlToValidate="txt"
ErrorMessage="Enter a valid dollar amount" ValidationExpression="\d+\.\d{2}" />So plan your interface accordingly.
