ASP. NET TextBox maxlength using VB.NET

Here we will see that how we can turn a TextBox font red after max length characters have been inserted, and also we check number of character has been inserted in the TextBox.
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Here we will see that how we can turn a TextBox font red after maxlength characters have been inserted, and also we check number of character has been inserted in the TextBox. But if we go back to a black font color if they were to delete back to less than maxlength.

Drag and drop a TextBox on the page. Select TextBox and press F4 to property window.

TextMode="MultiLine"

Now add the following code in the Head section of the .aspx page.

<head runat="server">

   <title></title>

   <style type="text/css">

       .validentry

        {

           background-color:#FFFFFF;

           color#000000;

        }

       

       .invalidentry

        {

           background-color:#FFCCCC;

           color#ff0000;

        }

   </style>

 

   <script language="javascript">

       function textCounter1(field, maxlimit) {

           if (field.value.length > maxlimit) {

                field.value = field.value.substring(0, maxlimit);

                document.getElementById('message').className = "invalidentry";

                document.getElementById('message').focus();

               //alert('You have reached your maximum character limit.');

            }

           else {

                document.getElementById('message').className = "validentry";

            }

          

        }

  

           function textCounter(field, countfield, maxlimit) {

               if (field.value.length > maxlimit)// if too long...trim it!

                    field.value = field.value.substring(0, maxlimit);

               else

                    countfield.value = maxlimit - field.value.length;

            }

   </script>

</head>

 

Now add the following code in the body section.

 

 

 

<body bgcolor="#FFFFFF">

<form name="blah" action="" method="post" runat="server">

   &nbsp;<asp:TextBox ID="message" runat="server" name="message"onkeydown="textCounter(this.form.message,this.form.remLen,120)"

       onkeyup="textCounter1(this.form.message, 120)" class="validentry"

       Height="101px" TextMode="MultiLine" Width="228px"></asp:TextBox>

   <br />

   <input readonly type="text" name="remLen" size="3" maxlength="3" value="120"

   position: absolutestyle="width: 34px">Character left<br />

   <br />

   <br />

   </form>

</body>

Now run the application.

txtbox1.gif
 

Figure1

Now check number of character has been inserted in the TextBox.

txtbox4.gif
 

Figure2 

Now we can turn a TextBox font red after max length characters have been inserted in TextBox.

txtbox3.gif
 

Figure3 

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