Using TextBoxWatermark With Validation Controls (C#)
The TextBoxWatermark control in the AJAX Control Toolkit extends a text box so that a text is displayed within the box. When a user clicks into the box, it is emptied. If the user leaves the box without entering text, the prefilled text reappears. This may collide with ASP.NET Validation Controls on the same page, but these issues may be overcome.
Overview
The TextBoxWatermark control in the AJAX Control Toolkit extends a text box so that a text is displayed within the box. When a user clicks into the box, it is emptied. If the user leaves the box without entering text, the prefilled text reappears. This may collide with ASP.NET Validation Controls on the same page, but these issues may be overcome.
Steps
The basic setup of the sample is the following: a TextBox control is watermarked using a TextBoxWatermarkExtender control. A button triggers a postback and will later be used to trigger the validation controls on the page. Also, a ScriptManager control is required to initialize ASP.NET AJAX:
[!code-aspxMain]
1: <form id="form1" runat="server">
2: <asp:ScriptManager ID="asm" runat="server" />
3: <div>
4: <asp:TextBox ID="Name" runat="server" /> <br />
5: <asp:Button ID="btn" runat="server" Text="Submit" OnClick="btn_Click" /><br />
6: <asp:Label ID="lbl" runat="server" />
7: </div>
8: <ajaxToolkit:TextBoxWatermarkExtender ID="tbwe" runat="server"
9: TargetControlID="Name" WatermarkText=" Your Name " />
10: </form>
Now add a RequiredFieldValidator control that checks whether there is text in the field when the form is submitted. The InitialValue property of the validator must be set to the same value that is used in the TextBoxWatermarkExtender control: When the form is submitted, the value of an unchanged textbox is the watermark value within it:
[!code-aspxMain]
1: <asp:RequiredFieldValidator ID="rfv1" ControlToValidate="Name"
2: Text="*" InitialValue=" Your Name " Display="Dynamic" runat="server" />
However there is one problem with this approach: If the client disables JavaScript, the text field is not prefilled with the watermark text, therefore the RequiredFieldValidator does not trigger an error message. Therefore, a second RequiredFieldValidator control is required which checks for an empty text box (omitting the InitialValue attribute).
[!code-aspxMain]
1: <asp:RequiredFieldValidator ID="rfv2" ControlToValidate="Name"
2: Text="*" Display="Dynamic" runat="server" />
Since both validators use Display="Dynamic", the end user cannot distinguish from the visual appearance which of the two validators was fired; instead, it looks like there was only one of them.
Finally, add some server-side code to output the text in the field if no validator issued an error message:
[!code-aspxMain]
1: <script runat="server">
2: protected void btn_Click(object sender, EventArgs e)
3: {
4: lbl.Text = HttpUtility.HtmlEncode(Name.Text);
5: }
6: </script>
The validator complains that there is no text in the field (Click to view full-size image)
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