Here I have explained how we can do enforce minimum and maximum character length validation in ASP.Net TextBox control using ASP.Net RegularExpressionValidator.
Maximum character length Validation (Maximum 8 characters allowed)
<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "TextBox1" ID="RegularExpressionValidator1" ValidationExpression = "^[\s\S]{0,8}$" runat="server" ErrorMessage="Maximum 8 characters allowed."></asp:RegularExpressionValidator>
Minimum character length Validation (Minimum 8 characters required)
<asp:TextBox ID="TextBox2" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "TextBox2" ID="RegularExpressionValidator2" ValidationExpression = "^[\s\S]{8,}$" runat="server" ErrorMessage="Minimum 8 characters required."></asp:RegularExpressionValidator>
Minimum and Maximum character length Validation (Minimum 5 and Maximum 8 characters required)
<asp:TextBox ID="TextBox3" runat="server"></asp:TextBox>
<asp:RegularExpressionValidator Display = "Dynamic" ControlToValidate = "TextBox3" ID="RegularExpressionValidator3" ValidationExpression = "^[\s\S]{5,8}$" runat="server" ErrorMessage="Minimum 5 and Maximum 8 characters required."></asp:RegularExpressionValidator>
Demo
