order of execution of page_load in a base and derived classes

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z. f. - 01 Sep 2004 14:23 GMT

Hi,

i have a class that is derived from System.Web.UI.Page, and this is the
class i use in my application as PageBase.
all other page classes are deriverd from my PageBase instead of the original
System.Web.UI.Page in order to have common checks in the page base.

i make securirty checks in the page base page_load event.
if the security fails, i can do whatever i want before the "real" / derived
page gets to be executed.

but i have noticed that the derived page load event gets to be called before
the base page load event.

so i have a problem.

i can cancel the use of page_load in my derived pages, but i use this
function to check on PostBack events that does not have server (like button)
event handler, but there when will i move it to?

is this the correct execution order - the derived gets to called before the
base?

is this also the order of execution in inheritence or only with delegated
event handlers? ( i mean when you use the syntax of Page.onLoad +=
this_onLoad )....

TIA, z.

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Ignacio Machin \( .NET/ C# MVP \) - 01 Sep 2004 13:47 GMT

Hi,

I have never been in this situation, but the first thing I would try is in
the Form.OnInit move the base.OnInit to the start of the method, before
register the Load handler for the current page.

cheers,

Signature

Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

> Hi,
>
[quoted text clipped - 24 lines]
>
> TIA, z.

Reply to this Message

Karl - 01 Sep 2004 13:54 GMT

Please don't cross-post.

I'm assuming you are using C# 'cuz you wouldn't have this behaviour in
VB....anyways, the simplest solution is to go into your derived page's
OnInit function in the "Web Form Designer generated code" region, and change
the order of the two executions:

InitializeComponent();
base.OnInit(e);

to

base.OnInit(e);
InitializeComponent();

This will cause the base page's init to load first, which will cause it's
Load event to get hooked up first, thus causing it to fire first.

Karl

> Hi,
>
[quoted text clipped - 24 lines]
>
> TIA, z.

Reply to this Message

z. f. - 01 Sep 2004 15:07 GMT

i use vb.net
and i don't override the OnInit method in my PageBase.

> Please don't cross-post.
>
[quoted text clipped - 49 lines]
> >
> > TIA, z.

Reply to this Message

Karl - 01 Sep 2004 15:17 GMT

Can you show me some code? If I do this:

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Trace.Write("derived load")
end sub

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
Trace.Write("baseload")
end sub

the base load always fires first.

Karl

> i use vb.net
> and i don't override the OnInit method in my PageBase.
[quoted text clipped - 54 lines]
> > >
> > > TIA, z.

Reply to this Message

z. f. - 01 Sep 2004 15:42 GMT

also

from the IL created by VB compiler you see that in the constructor it is
adding the event handler:

Public Sub New()
AddHandler MyBase.Load, New EventHandler(AddressOf Me.Page_Load)
End Sub

> Please don't cross-post.
>
[quoted text clipped - 49 lines]
> >
> > TIA, z.

Reply to this Message

Ignacio Machin \( .NET/ C# MVP \) - 01 Sep 2004 19:03 GMT

Hi,

IIRC the Page_Load is added in the OnInit handler:

override protected void OnInit(EventArgs e)
{
InitializeComponent();
base.OnInit(e);
}
private void InitializeComponent()
{
this.Load += new System.EventHandler(this.Page_Load);
}

Cheers,

Signature

Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

> also
>
[quoted text clipped - 60 lines]
> > >
> > > TIA, z.

Reply to this Message

z. f. - 02 Sep 2004 08:03 GMT

you mean in c# don't you?
it is no question, it's a fact VB does it the way i showed, you can't
control it.

"Ignacio Machin ( .NET/ C# MVP )" <ignacio.machin AT dot.state.fl.us> wrote

> Hi,
>
[quoted text clipped - 79 lines]
> > > >
> > > > TIA, z.

Reply to this Message

Ignacio Machin \( .NET/ C# MVP \) - 02 Sep 2004 14:59 GMT

Hi,

Yes, the code I shown was in C#, I havent worked at all with VB but this is
the code the designer created :

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
End Sub

I don;t know much about how the event is hooked , but I can bet it's done
in the constructor as you said.

Again the virtual method approach can help you in this escenario.

cheers,

Signature

Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

> you mean in c# don't you?
> it is no question, it's a fact VB does it the way i showed, you can't
[quoted text clipped - 88 lines]
> > > > >
> > > > > TIA, z.

Reply to this Message

Ignacio Machin \( .NET/ C# MVP \) - 01 Sep 2004 13:58 GMT

Hi again

I'm not very sure that the previous answer will solve the problem, IIRC
the order of execution of the handlers is not defined. therefore even ify ou
register first the parent you may get the derived executing first after all.

Therefore you have to use another approach, you could use a virtual method
that you call in the OnLoad event, so each class Page) define what needs to
be checked , being the trick to verify the parent first to have the first
line calling the parent method:
protected override Check()
{
parent.Check();
//do the checking
}

I think this will solve your problem.

Cheers,

Signature

Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

> Hi,
>
[quoted text clipped - 24 lines]
>
> TIA, z.

Reply to this Message

Benjamin Schwitter - 01 Sep 2004 14:20 GMT

We had the same problem with the Page_Load Event.

We solved it similar to the way Ignacio Machin describes using the OnLoad
event.

Good luck,

Benjamin Schwitter

"Ignacio Machin ( .NET/ C# MVP )" <ignacio.machin AT dot.state.fl.us> wrote

> Hi again
>
[quoted text clipped - 49 lines]
> >
> > TIA, z.

Reply to this Message

z. f. - 01 Sep 2004 15:08 GMT

i wouldn't like to add code to each page-class i add.
the idea behind using a PageBase is to not change the way i write the other
pages, just let them use the services the PageBase implement without even
"knowing" anout it.

"Ignacio Machin ( .NET/ C# MVP )" <ignacio.machin AT dot.state.fl.us> wrote

> Hi again
>
[quoted text clipped - 49 lines]
> >
> > TIA, z.

Reply to this Message

Ignacio Machin \( .NET/ C# MVP \) - 01 Sep 2004 19:07 GMT

Hi,

You add it where you need it. each page's method should be responsible to
handle the functionalities implemented on it. All you have to do is call the
method in the Page_Load.

Why is that not ok with you?

cheers,

Signature

Ignacio Machin,
ignacio.machin AT dot.state.fl.us
Florida Department Of Transportation

> i wouldn't like to add code to each page-class i add.
> the idea behind using a PageBase is to not change the way i write the other
[quoted text clipped - 60 lines]
> > >
> > > TIA, z.

Reply to this Message

- 02 Sep 2004 14:17 GMT

> Hi,
>
[quoted text clipped - 24 lines]
>
> TIA, z.

Your classes dont work the way you would like. The ASPNET engine works with
your derived classes & calls the overriding methods in them, it couldn't
care about base classes ( I suppose it has to be System.Web.UI.Page
eventually) .
The effect you want only happens with new() where the 1st line in the
suboutine is either a call to one of the base classes constructors or an
implicit call to its parameterless constructor. So if you can put your
initialisation in the base classes new() then it should be fixed. However I
dont think all the ASP features are ready at that time, I also dont know if
any page object is reused for subsequent requests which could possibly lead
to some speedup but probably lead to hours of extra debugging. Maybe that
could be added by use of an attribute ?

Signature

Jonathan Bailey.

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order of execution of page_load in a base and derived classes

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