How to resize textbox automatically according to text size without scrolling

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Hi,

I have a problem on resizing the asp.net textbox automatically according to text growing size which is retrieve from database.
Problem is Until i scroll or press the enter key the textbox wont resize. Any idea or hint to fixed this issue will be greatly appreciated.Thank you

What I have tried:

1. Control declaration:

ASP.NET

<asp:TextBox ID="txtrez" runat="server" width="100%" CssClass="img-responsive center" Text='<%# Eval("imgtext") %>' TextMode="MultiLine" style="resize:none;overflow:hidden; text-align:center" ReadOnly="True" onkeyup="AutoExpand(this)" Rows="2" BorderStyle="None"></asp:TextBox>

2. JavaScript function:

<script type="text/javascript">
function AutoExpand(txtbox) {
txtbox.style.height = "1px";
txtbox.style.height = (25+ txtbox.scrollHeight) + "px";
}
</script>

Posted 11-Jun-16 3:18am

Kasar_7

Updated 11-Jun-16 4:32am

v2

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Sergey Alexandrovich Kryukov · Answer 1 · 2016-06-11T04:32:00

Here is the simplest sample

HTML

<html>
   <head>
      <title>Adaptive input width sample</title>
      <style type="text/css">
         #meter { visibility: hidden; padding-left: 1em;
                  font-family: serif; font-size: 12pt; border: thick solid; }
         input { padding-left: 0.5em; font-family: serif; font-size: 12pt; }
      </style>
   </head>
<body>

<input id="test" type="text"/><span id="meter"/>

<script>

   setWidthSync(
	document.getElementById("test"),
	document.getElementById("meter"));

   function setWidthSync(target, meter) {
      var adjustWidth = function() {
         meter.innerHTML = target.value;
         target.style.width = meter.offsetWidth;
      };
      adjustWidth();
      target.onkeydown = function() { adjustWidth(); };
      target.onkeyup = function() { adjustWidth(); };
   } //setWidthSync

</script>

</body>
</html>

The idea is: you are using the hidden element meter (span, in my example) to measure actual width of the same text. The results can be slightly inaccurate due to different styles of the elements, so they should be kept close, via CSS style, with enough padding value for the meter element.

Also, this sample shows some flicker, because the modified text is rendered first, and only then the width of input is adjusted. Besides, the width is not accurately calculated, if a user inputs several blank space character in a row, because in HTML rendering such sequences are always rendered as one blank space. I'll leave improving this code for your home exercise. I hope you got the idea. :-)

—SA