In Asp.net, The ispostback attribute is often used to determine whether it is intended to be sent back. Many people say that the pageload event must contain
Protectedvoidpage_load (objectsender, eventargs E)
{
If (! Ispostback)
{
}
}
But I really don't understand the reason. It must be true, but isn't it wrong in the previous example? Therefore, you must understand the principles ~~ To clarify this, we do not need to use HTML + handler to process Asp.net pages.ProgramTo clarify this, I will firstCodeHtml
<Htmlxmlns = "http://www.w3.org/1999/xhtml">
<Head>
<Title> </title>
</Head>
<Body>
<Formaction = "hello2.ashx" method = "Post">
<Inputtype = "hidden" name = "ispostback" class = "night" value = "true"/>
Name: <inputtype = "text" id = "fasdfasd" name = "username" value = "@ value"/> <inputtype = "Submit" value = "Submit"/>
@ Msg
</Form>
</Body>
</Html>
Handler's
Publicvoidprocessrequest (httpcontext context ){
Context. response. contenttype = "text/html ";
Stringusername = context. request ["username"];
Stringmsg = "";
Stringispostback = context. request ["ispostback"]; //
If (ispostback = "true") // if this parameter is submitted, it indicates that the form is submitted.
{
Context. response. Write ("Submit to enter ");
MSG = username + "hello ";
}
Else
{
Context. response. Write ("go directly ");
Username = "";
MSG = "";
}
Stringfullpath = context. server. mappath ("hello2.htm"); // obtain the full path of the file.
Stringcontent = system. Io. file. readalltext (fullpath); // read the file
Content = content. Replace ("@ value", username );
Content = content. Replace ("@ MSG", MSG );
Context. response. Write (content );
}
Publicboolisreusable {
Get {
Returnfalse;
}
}
I believe you will understand what is going on at a Glance. I will probably describe how to run handler first because context is run for the first time. request ["ispostback"]; it must be empty. Therefore, you can directly access and then read HTML to output the content to the page (placeholder @ value and so on) to simulate Asp.net in order to save the page status)
In this case, when a vertex is submitted, the ispostback is always true because of the following statement. <inputtype = "hidden" name = "ispostback" class = "night" value = "true ""/>
This has caused many people to say that ispostback is to determine whether it is the first time you enter. In fact, after you enter the site, refresh will still find that ispostback is not true because it has not been submitted to implement a sending back.
This is a bit messy ~~ But the basic principle is as follows, hoping to help new users.
Let's take a look at the above Code and copy it and try it ~ Do not understand the following message. Welcome to discuss it.
Here is a supplement
Protectedvoidpage_load (objectsender, eventargs E)
{
If (! Ispostback)
{
// Perform data binding.
}
}
Bind data to reduce unnecessary interaction with the database.
If this parameter is not added, page_load is executed before the event is executed every time you click the button.
This causes resource fees for Data Binding and database interaction when the button is executed.
However, this judgment does not cause this problem ~~
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