Introduction to the role of hidden fields in html and usage examples_HTML/Xhtml_Web page production

Basic syntax:



Function:

1 Hidden fields are invisible to users on the page. The purpose of inserting hidden fields into forms is to collect or send information so that it can be used by the program that processes the form. When the viewer clicks the send button to send the form, the hidden field information 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 session key, etc. Of course, these things can also be implemented using cookies, 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, we first check the value of the command and we will know which one the user clicked. button 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 be 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

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The code is as follows:

-->

@n

Use general handlers to implement

value auto-increment.ashx

Copy code

The code is as follows:

int n = 0;
public void ProcessRequest (HttpContext context) {
context.Response.ContentType = "text/html";

string path = context.Request.MapPath("Number increases.htm");
string html = System.IO.File. ReadAllText(path);
//Determine whether the page is loaded for the first time
string viewstate = context.Request.Form["_viewstate"];
if (!string.IsNullOrEmpty(viewstate))
{
//Click the button post
//Get the value of the hidden field
string s = context.Request.Form["_div"];
if (int.TryParse(s, out n ))
{
n ;
html = html.Replace("@n",n.ToString());
}
}
else
{
//The page is loaded for the first time, assign values ​​to the div and the hidden fields corresponding to the div
html = html.Replace("@n", n.ToString());
}
context.Response.Write( html);
}