配合，这是一个基本问题，在发布基本问题之前，应先在搜索引擎中进行搜索.将 Maxlength ="50" 设置为相应的文本框.

Mate, It''s a basic question, you should search in search engines before you posting basic questions. Set Maxlength="50" to that appropriate Textbox.

可以采用多种方法.

1.设置MaxLength(上面已经建议过)
2.使用Javascript跟踪基于onchange/onkeypress事件填充的字符
3.使用正则表达式验证器小心
4.使用Masked文本框(内部实现选项2/3)

There can be various ways to do it.

1. Setting MaxLength (already suggested above)
2. Use Javascript to track the characters filled based on onchange/onkeypress events
3. Use Regular Expression Validators to take care
4. Use Masked textboxes (option 2/3 is internally implemented)

Sandeep是正确的.
有多种方法可以实现.
如果您想使用javascript Heres验证您的用户输入，请使用基本功能

Sandeep is correct.
there are various ways to do it.
if you want to validate your user input using javascript heres a basic function

<script type="text/javascript">

function validate() 
{ 
    if (document.getElementById('txt').value.length > 50) 
    { 
        alert("error message"); return false 
    }
}
</script>

<input type="text" id="txt" />
<input button="submit" onclick="return validate();" />