What are the main differences of defining a control statically or creating it dynamically on page load?

I am working on a project which creates controls dynamically for a form in the page_load event, loads in their current values from the database and saves their values (using FindControl) when the user clicks the continue button.

When I added a control statically in the .aspx page and followed their same procedure of loading the value in the page load and saving it on the button press I found that the value would not save correctly. It seems that it wouldn't save because the click event fires after the page_load, so the page_load of the post back reverted the value and the user entered value was not saved.

The strange th开发者_如何学JAVAing is that by changing the control to be dynamically created just as all the other controls on the page and keeping the loading and saving the same it now works. Even though the page load still creates the control with the old database value.

It seems like a very fundamental asp .net feature here but i'm just unclear as to what is going on. I suspect it is to do with the timing of creation and maybe when the view state kicks in.

Static page controls are created just like dynamic page controls. The difference might be coming in your Page_Load. Whenever you postback all the controls are created afresh which means they are created with their initial values. This happens because after creating the controls asp.net throws away the controls/objects.

So, when the request comes, the first thing that asp.net does it to recreate the controls by looking at their definitions (in the designer files). On each postback they are created and initialized again losing their state in the process.

But after creating the controls Asp.Net loads any viewstate that is sent along with the request which makes people think that the state is always saved at the server.

What might be happening is that either the viewstate is not enabled for your control (in case they are created in designer), in which case you may try using EnableViewState property to true of the control.

Or, when you're doing a Page_Load, you're forcefully re-initializing everything. And in process losing all the control data. If you could post the logic of Page_Load, it might get clarified.

Make sure that:

• you are not setting the value again for the static control in Page_Load. The dynamic control are probably getting around it by grabbing the ViewState and form values at a different stage in the lifecycle.
• The dynamic controls are added After the static control. Or at least they are added in a different container. Placement in the control's collection can affect the ViewState, although it doesn't look like your scenario / since what you mention seems to be more about the values in the current post.
• The save is happening After the Page_Load in response to the corresponding event.

I've run into similar problems in the past (quite a few times actually), but what helped me the most is understanding the ASP.NET Page Lifecycle.

Microsoft has an article on it which describes it pretty well, but this post by Solomon Shaffer really cleared up everything.

I suggest reading them both and coming back with additional questions regarding to a particular state, when to load/save data etc..

Hope this helps.

Marko

Note that you may want to use Page.IsPostBack property to avoid reinitializing values on button clicks and other events.

private void Page_Load()
{
    if (!this.IsPostBack)
    {
        // Assign values to the controls.
    }
}