ASP .net PostBack and Function

Question

I'm working on a web page, I need that when it loads first time it would get data from api's.

Then I want to go from page to page with the same data.

I used IsPostBack

Page_Load(object sender, EventArgs e)
{
        if (!Page.IsPostBack)
        {
            //First Time Load Data
            leadsList = new List<Lead>();
            var client = TVPLeads.Session.GetWebClient(Session);
            string PostId = PostId = Request.QueryString["postId"];
            PostId = "1";
            try
            {
                leadsList = API.GetPostLeads(client, PostId);
            }
            catch (Exception) { }
            page = (page == 0) ? 0 : page - 1;
            DisplayLeadsPage(leadsList, page, "");

        }

}

private void pageChoosen(object sender, EventArgs e)
{
    int page = int.Parse(((Button)sender).CommandArgument);
    DisplayLeadsPage(leadsList, page-1, "");
}

DisplayPagination(){
.
.
 Button prev = new Button{
                    ID = "page_"+i,
                    CssClass = "Pagination",
                    Text = "i",
                    CommandArgument = ""+i,
                    OnClientClick = "pageChoosen"
                };
                prev.Click += pageChoosen;

                divPagination.Controls.Add(prev);
.
.
.
}

I clicking on a button , got to Page_Load function the postBack is true as expected , but the function is not firing(checked with debugger).

if I remove the IsPostBack and it would make all over again , then the button function is firing.

What's the problem with that? How to use it right ?

I don't understand the problem. You state that `IsPostBack` is `true` as expected. Your condition says to only run the code if `IsPostBack` is `false`. — Craig W., Feb 05 '15 at 21:37
Yes , but button was clicked , And it does go to it's function. If I remove the if(postBack) it's working. — Igor Gumush, Feb 05 '15 at 21:38

Christos · Accepted Answer · 2015-02-24T22:54:39.410

The first time you request your page, your page is not posted back. The rendering engine of asp.net creates the page and sends it back to the client.

When you click a button then this click we trigger a postback and a handler that is defined the Page class will execute some code. Then the page will be build and when on Page_Load comes into the scene, the code that is in the if(!Page.IsPostBack) will not be executed, because the IsPostBack property of the Page class is true.

There are two key concepts to conceive there. The first is about the Page lifecycle, the events that the page goes through in each request.

The second is that the Page is not posted back only the first time the client requests it (or the times that she does a full refresh of the page, clicking F5 for instance in Chrome).

Update

Respond to button click

If you haven't defined a server side button, you should define one. How?

In you markup, just add the following line of code:

<asp:Button id="buttonId" Text="Submit" runat="server" />

Then in the designer double click on the button. As you will notice, you will be navigated to the code behind class and a method would have been created, which would be the click handler. Then inside the body of this method, you could write the commands that should be executed, when the user clicks on your button. If you now go back to your markup, you will notice the another attribute would have been added to the Button with name OnClick.

Update

Dynamically built buttons need to be created again when the page is posting back. Otherwise they won't work.

ok , that what I wanted, but how to make it to executed my function — Igor Gumush, Feb 05 '15 at 21:51
@IgorGumush That depends on when you want to execute it. Should it execute when the page loads the first time? Or in respond to clicking a button? — mason, Feb 05 '15 at 21:58
You were right, please add to your answer that dynamically built buttons need to be created again when the page is posting back. Otherwise they won't work — Igor Gumush, Feb 24 '15 at 22:46

jrjensen · Answer 2 · 2015-02-05T22:00:46.757

1

Try adding an event handler to the control.

Your control will look something like this (on the aspx page):

<asp:button id="YourButton" runat="server" OnClick="YourButton_Click" />

Then your backend handler should also be public:

public void YourButton_Click(object sender, System.EventArgs e) {

Edit: You can also do this:

leadsList = new List<Lead>();

if (!Page.IsPostBack)
{
    ...
}
else
{
    page = (page == 0) ? 0 : page - 1;
    DisplayLeadsPage(leadsList, page, "");
}

edited Feb 05 '15 at 22:00

answered Feb 05 '15 at 21:45

jrjensen

191
9

@IgorGumush Please edit your question so show that (make it clear which is your updated code) – mason Feb 05 '15 at 21:54
The problem is that if i'm not getting to the function I don't know witch page to show – Igor Gumush Feb 05 '15 at 22:11
So you want to call the DisplayLeadsPage function if there is a post back, correct? – jrjensen Feb 05 '15 at 22:21

score 0 · Answer 3 · answered Feb 07 '15 at 13:05

0

Found an answer for the problem.

When the page is posted back to server. I need to rebuild the controls Otherwise, those controls will be null.

answered Feb 07 '15 at 13:05

Igor Gumush

61
2
10

ASP .net PostBack and Function

3 Answers3