user control and page not responding to events

[Scally84]

Hi again,

I'm currently (re)creating a "classic" ASP site into an ASP.net site. Off course I encountered some typical problems, and one of them was the "include" problem. The older ASP site uses A LOT of includes and so I tried to find a decent ASP.net solution. I read on this site that ASP.net uses user controls to replace them, and so I changed it in my source code. For example I have 2 pages, one which I use as a header and one which I use to display my content. The header uses a textfield and a button where users can enter keywords. This button uses an onclick event which calls a javascript function. The other page uses a dropdownlist and a datagrid. When someone picks a value from the dropdownlist the datagrid should be renewed. This page uses both javascript and visual basic functions to handle events. Both pages (and events) worked fine until I started using user controls instead of includes. The layout of both pages was remained... but every control with an event on my page now had problems. The header didn't call the javascript any more, when a value of the dropdownlist was selected the datagrid wasn't renewed and the dropdownlist changed the selected value back into it's original (standard) value, so in other words the dropdownlist was initiated (don't know if this is the correct word i mean a verb for initialisation) again. I thought perhaps this was a one of kind problem but when I started transforming other pages with user controls they had the same problem. Another page to upload files had a button which didn't respond anymore to the onclick event. Does someone know what the problem is?

I've considered using a global class/file where all code is stored instead of includes but what to do then with the html code... I fear this will change my layour majorly. So I don't think this is an option.

Another remark I have: as I mentioned earlier the older ASP pages use A LOT of includes: for example a certain file includes 2 files and those files include 4 files and each of these files include another 2 files... can I just replace all of them by user controls?

Hope someone can help...

Scally

 

[ca8msm]

I think your main problem here is that you are probably binding your dropdownlist on the page load event and therefore it is getting reset each time (hence your problem of the control being "initiated" again).

To explain further (and hopefully help you understand the problem) consider this example/walkthrough:

1) Create new webpage
2) Add to button to the page
3) Create a new user control
4) Add a dropdownlist to the user control
5) Add this code to the user control

    Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Put user code to initialize the page here
            DropDownList1.Items.Clear()
            For i As Integer = 0 To 10
                DropDownList1.Items.Add(i)
            Next
    End Sub

6) Add the user control to the page

Now, when you run the page you will see that the dropdownlist is populated with 10 items. If you select an item (number 5 for example) and click the button, you will see that the page posts back to itself and the dropdownlist is reset to zero (this is because the page load event of the user control has been run again).

If you change the event to look like:

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        'Put user code to initialize the page here
        If Not Page.IsPostBack Then
            DropDownList1.Items.Clear()
            For i As Integer = 0 To 10
                DropDownList1.Items.Add(i)
            Next
        End If
    End Sub

and retry the test, the dropdownlist will keep the value of what you selected (as the page load event only runs if it is not a postback).

Hope this helps

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[Scally84]

Thank you I've tried this but that isn't the problem... this is how my page looks like:

'codebehind
If Not(Me.IsPostBack) then
       *fill dropdownlist*
       
       *call function to show dropdownlist*

       response.write("test")
End If

Sub DropDownListDepts_SelectedIndexChanged(sender as Object, e as EventArgs)
       *call function to renew dropdownlist*
End Sub
'html
<asp:DropDownList id="DropDownListDepts" runat="server" OnSelectedIndexChanged="DropDownListDepts_SelectedIndexChanged" AutoPostBack="True"></asp:DropDownList>

       *user control*

I've put the response.write statement into my page_load to view what result it would give and now I really don't understand it... The first time the page is loaded it displays the "test" message and the dropdownlist is filled, but then I select a value from the dropdownlist and the page posts back the "test" message is gone and my dropdownlist is again initiated

Scally

 

[Scally84]

edit: in my post above *call function to show or renew dropdownlist* should be *call function to show or renew DATAGRID*

 

[ca8msm]

It's probably because you bind the data in the dropdownlist selectedindexchanged event (this runs after the page load so you will be resetting it each time).

To get a grasp on how user controls and pages work in ASP.NET you should read some of the articles on aspnet.4guysfromrolla.com/ and also run your program in debug mode and set breakpoints on each event to see the order that they run in.

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[Scally84]

The problem isn't the dropdownlist selectedindexchanged event either. I placed a response.write statement into this event and I discovered that this event isn't raised at all... so I removed the header (usercontrol) and everything worked fine. So I must refer to my first question: why do all events stop working when I use my user control? I already read several articles on 4guysfromrolla... and I think the problem is something with the <form> tags which I use both in the header and the other page. Perhaps I'm doing something wrong with this... perhaps the compiler can only process one form tag or something...

 

[ca8msm]

perhaps the compiler can only process one form tag or something...

A page can only contain one <form runat="server"> tag so if you have multiple ones it will error.

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[Scally84]

ok... but what is the problem then? why doesn't my website respond on events when I use user controls? doesn't anyone have a clue?

 

[ca8msm]

doesn't anyone have a clue?

Yes we do but you are going to have to do some investigating yourself. I've explained in very basic terms about postbacks (and given you an example of how they work) and also told you to "run your program in debug mode and set breakpoints on each event to see the order that they run in". Once you do this you should be able to see the status of the page when each event fires and then you will have to step through each event and see why it isn't firing as you expected it to. Until you have done this, and have grasped this concept, there is nothing further we can help you with.

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[Scally84]

The first thing I do when I have a problem is look for solutions on the internet, by reading articles and searching information on google. IF I post my question on this forum that means I'm really stuck and I hope someone over here can help me... I've been busy with this problem for over a week now and most of the time I've been reading solutions but none of them seemed to work. I do not have problems with postbacks because I've worked with postbacks right from the start. I totally understand how this works (its not THAT hard to understand you know). And I can't just "run my program in debug mode and set breakpoints" because I don't use IIS on my computer. (we have a very strict policy about installing software so I don't have IIS on my local computer) So I make/update my pages manually with notepad... and test them by uploading it to our server. That's what makes it so hard to find where the error is... I can use response.write statements but that's about it. There must be something about user controls that I've overlooked?

 

[ca8msm]

I do not have problems with postbacks because I've worked with postbacks right from the start. I totally understand how this works

It seems to me that if you have a control (whether that is part of a user control or not) that is being "reset" each time the page posts back to the server, then you do have a problem with postbacks of some sort.

And I can't just "run my program in debug mode and set breakpoints" because I don't use IIS on my computer. (we have a very strict policy about installing software so I don't have IIS on my local computer) So I make/update my pages manually with notepad... and test them by uploading it to our server

This is obviously your biggest hurdle and what is stopping you from finding the problem (and if you can't step through the code to find the problem then we have little chance of adding anything meaningful apart from explain the basics of how it works - which I have attempted to do by demonstrating how a user control works). I would suggest taking this "theory" on how user controls work, build up a basic example that works and then apply the needs of your application to it. Only by doing this step-by-step approach you should be able to determine where/when the controls don't start working as you expected.

The "strict policy" of not allowing the developers to have a development environment is both strange and unprofessional and unless you want to come across hurdles like this everytime you develop an application or webpage then you need to come to come up with an agreement with your company that allows you to either install a program (such as VS for example) on a development environment or an existing server.

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[cappmgr]

I got burned once because there was put a Page.DataBind() in a usercontrol.
Marty