Detailed explanation of the role of hidden fields in HTML and usage sample codes

Hidden fields are invisible to users on the page. The purpose of inserting hidden fields in the form is to collect or send information so that it can be used by the program that processes the form. The following is a detailed introduction to the actual use of this hidden field. Friends who are interested in how to use it, don’t miss it. Basic syntax:



Function:

1 Hidden fields are invisible to users on the page. The purpose of inserting hidden fields into the form is to collect or send information to facilitate processing. The form is used by the program. When the viewer clicks the Send button to send the form, the information in the hidden field is also sent to the server.

2 Sometimes we need to give the user information to determine the user's identity when submitting the form, such as sessionkey, etc. Of course, these things can also be implemented using cookie, but it is much simpler to use hidden fields. And there will be no worries about browsers not supporting it and users disabling cookies.

3 Sometimes there are multiple submit buttons in a form. How can the program distinguish which button the user pressed to submit? We can write a hidden field, and then add onclick="document.form.command.value="xx"" to each button. Then after we receive the data, Checking the value of command will tell you which button the user pressed to submit.

4 Sometimes there are multiple forms in a web page. We know that multiple forms cannot be submitted at the same time, but sometimes these forms do interact with each other. We can add hidden fields in the form to connect them. .

5 javascript does not support global variables, but sometimes we must use global variables, we can store the value in the hidden field first, and its value will not Lost.

6 There is another example. For example, four small windows pop up when you press a button. When one of the small windows is clicked, the other three automatically close. However, IE does not support small windows calling each other, so you can only write a hidden field in the parent window. When the small window sees that the value of the hidden field is close, it will close itself.

Example: Use hidden to increase the number by 1 when clicking the submit button

The value increases automatically.htm

The code is as follows:

<form action="数值自增.ashx" method="post"> 
<input type="hidden" name="_viewstate" value="a" /> 
<input type="hidden" name="_p" value="@n" /> 
<!-- <input name="txt" type="text" value="@value" />--> 
<p>@n</p> 
<input type="submit" value="click" /> 
</form>

Use the general handler to realize

Numerical self-increment.ashx

The code is as follows:

int n = 0; 
public void ProcessRequest (HttpContext context) { 
context.Response.ContentType = "text/html"; 
string path = context.Request.MapPath("数值自增.htm"); 
string html = System.IO.File.ReadAllText(path); 
//判断页面是否是第一次加载 
string viewstate = context.Request.Form["_viewstate"]; 
if (!string.IsNullOrEmpty(viewstate)) 
{ 
//点击按钮 post 
//获取隐藏域的值 
string s = context.Request.Form["_p"]; 
if (int.TryParse(s, out n)) 
{ 
n++; 
html = html.Replace("@n",n.ToString()); 
} 
} 
else 
{ 
//页面首次加载,给p和p对应的隐藏域赋值 
html = html.Replace("@n", n.ToString()); 
} 
context.Response.Write(html); 
}

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