I'm a beginner in ASP.NET, just a question on page life cycle:
The MSDN doc says: "Raised after the page loads view state for itself and all controls, and after it processes postback data that is included with the Request instance", which means, I can also put the programming logic here
protected void Page_PreLoad(object sender, EventArgs e)
{
Label1.Text = "Hello World; the time is now " + DateTime.Now.ToString();
}
so why we always do like
protected void Page_Load(object sender, EventArgs e)
{
Label1.Text = "Hello World; the time is now " + DateTime.Now.ToString();
}
?
The Page_Load event handler will properly handle creation of all page controls. Per documentation:
The Page object calls the OnLoad method on the Page object, and then
recursively does the same for each child control until the page and
all controls are loaded. The Load event of individual controls occurs
after the Load event of the page.
Use the OnLoad event method to set properties in controls and to
establish database connections.
...which means, based on your example, the Label1.Text may get reset by that control's OnLoad event (depending on the individual control's implementation; I do not know if this is true for Label control, but it would be in compliance with the documentation if that did happen).
Related
May I know if there is any way to invoke a method from the child page(.aspx) after the page load of the user control is finished?
Right now I have an issue of being unable to retrieve the value from the child page because the variables from the user control has not been assigned the value yet.
To put it simply
FROM MY .ASPX FILE
Page_Load(object sender, EventArgs e)
{
x = getValueFromUserControl();
}
FROM MY USER CONTROL
Page_Load(object sender, EventArgs e)
{
int x = getvalueFromDatabase();
}
getValueFromuserControl()
{
return x;
}
Since the ASP.NET Life Cycle goes from the child page(.aspx) page_load -> user control page_load, I am unable to retrieve the value of x.
That said, ideally I would not like to put the function in the child page and call it from the user control as the user control is being used in other pages.
In short, I would like to invoke a method from my .aspx page after the page_load in my user control ends, Thank you!
Get the value at a later page event:
protected override void OnLoadComplete(EventArgs e) {
x = getValueFromUserControl();
}
Unless, of course, there is a specific reason why you must get the value on Page_Load. There are other, probably more appropriate ways to handle this, but without knowing what x is and what you need to do with it, it is hard to give any other advice. For example, maybe the UserControl should fire an event that is handled by the page.
I am working with C# web application. I want to know deeply about the page events. Because I thought that the page load event happens first (when a page is requested in browser). But when I tried with commenting the method protected void Page_Load(object sender, EventArgs e) the page get loaded without error.
off-course your webpage will work even if there is no Page_Load() method.
Before a Page_Load() events like PreInit, Init() etc are called. Refer to page life cycle.
Page_Load() method is called after a preLoad event. With Page_Load() you can set default values or check for postBacks etc.
protected void Page_Load(object sender, EventArgs e)
{
int x = 10;
}
write this and put a break-point on int x = 10; watch sender and e.
Every Page object has nine events, most of which you will not have to worry about in your day to day dealings with ASP.NET. The three that you will deal with the most are:
Page_Init
Page_Load
Page_PreRender
They do execute in the order given above so make sure to take that into consideration, especially when building custom controls. The reason you have to keep this in mind is because information might not be available when you expect if you do not deal with it appropriately.
Refer: Life Cycle
1.Page request
2.Start
3.Initialize
4.Load
5.Postback Event Handling
6.Rendering
7.Unload
This is the page life cycle.
Load event comes at 4th position.
You can check details over here:
http://msdn.microsoft.com/en-us/library/ms178472%28v=vs.100%29.aspx
I have an .aspx page which sends a letter to a customer if a button on that page is clicked. Onclick the page calls itself, so the mail send class is in the same file. However I do not want the mail sent when the page is simply loaded. I want it send the letter when the button is clicked, so, I'm trying with the following code:
void page_Load(Object sender, System.EventArgs e)
{
if (IsPostBack)
{
SendMail();
}
}
But it doesn't work. What am I doing wrong?
Why not use the Button's Click Event then?
What you are talking about is you want to send an email only when a specific button is clicked. Then why not register to it's click event instead of bloating your page_load with extra code?
Button's click event is raised only when that button's click causes a postback. So, that's your best option.
Make an event handler for the button's click event (Just double click the button in Visual Studio's Designer).
Using Page_Load will result in emails being sent out when the user posts back in any circumstance, not just your button click.
Looks like the page does not find the correct event handler for the Page_Load, check the case and correct it to Page_Load
See if this works (replace your page_Load method with the following code):
protected override void OnLoad(System.EventArgs e)
{
base.OnLoad(e);
if (IsPostBack)
{
SendMail();
}
}
You are currently relying on AutoEventWireup functionality to hook up your page events. This is slow and problematic and may be the cause of your issue. The method I gave you overrides Page.OnLoad and should correct the problem as well.
The Page_Load event is raised every time the page is posted, well by means of postback or callback, if you want to use server side events you should call you SendMail method in the button's click event:
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack && !IsCallback)
{
/*occurs the first time the page is loaded*/
}
if (IsPostBack)
{
/*occurs every time a postback is raised (e.g. by form submission) */
}
if (IsCallback)
{
/*occurs every time a callback is raised, e.g. by generating callbacks by means of AJAX/
}
}
protected void SendMail_Click(object sender, EventArgs e) { SendMail(); }
Read more at MSDN: ASP.NET Page Life Cycle.
I have a simple user control that contains some buttons that fire events which I want to be handled by the page using the control. I have my code setup as such:
public event EventHandler Cancel;
public event EventHandler Confirm;
public void Confirm_Click(object sender, EventArgs e)
{
if (Confirm != null)
Confirm(this, e);
}
public void Cancel_Click(object sender, EventArgs e)
{
if (Cancel != null)
Cancel(this, e);
}
but when I try to call these from the page that is using the control's page load event I don't get any of the custom events
ASPX Code
<%# Register TagPrefix="btg" TagName="CustomControl" Src="~/Search/CustomControl.ascx" %>
<btg:CustomControl ID="btgControl" runat="server" ></btg:CustomControl>
could this be because my buttons in the user control are within an update panel?
You shouldn't be seeing methods. You should be seeing events.
In your parent page's load, you need to do this:
myUserControl.Cancel += new EventHandler(myUserControl_Cancel);
You can hit tab,tab to auto-generate the method stub. That will look like:
void myUserControl_Cancel(object sender, EventArgs e) {}
Then, this code will fire after it is called in the method of your user control. In order for that code to fire, you'll have to assign the events to button events on your user control.
edit: myUserControl is the id of your user control. Also, some would argue that event handlers should be in your page's init method.
edit:
Is your user control properly referenced in the page? i.e. Are you registering the user control in web.config or using the reference directive in the page?
Also, did you try cleaning the solution and rebuilding? If your user control is dynamically created/loaded, you'll have to wire up the events in the same scope as the instantiated control. In order to dynamically load the user control, you'll have to have a placeholder in your page and do the following:
UserControl control = Page.LoadControl("~/ControlPath/ControlName.ascx");
((MyUserControlClass)control).Cancel += += new EventHandler(myUserControl_Cancel); // etc...
I'm experimenting with some AJAX now. I have a custom control which appears on my masterpage in which there is an update panel and a timer. The timer fires and the panel updates and everything is dandy. Except that there are some operations that I don't want it to perform on every refresh. It seems like the entire page lifecycle happens with each refresh. There are variables I want to set, and keep their value on the refresh. Is there a way to make it perform ONLY what's in the timer_tick call?
You could take a look at Request["__EVENTTARGET"] in the page load event to see what control caused the postback. If it's the timer control, jump out of the function.
Assuming your timer is called "refreshtimer":
protected void Page_Load(object sender, EventArgs e)
{
if (Request["__EVENTTARGET"] == "refreshtimer")
{
return;
}
// etc
Not sure what what an AJAX.Net post back looks like to, But I usually protect my other controls and content by checking for post back;
protected void Page_Load(object sender, EventArgs e)
{
// if its a post back then my controls should already be setup...
if (!Page.IsPostBack)
{
InitControlData();
}
}
and then it should fall thru to your event handling?
protected void timer_tick(object sender, EventArgs e)
{
// Do my Ajaxy work~
}
UpdatePanels always force the entire page to refresh. If you want only a certain portion of the page to be processed (and it's a fixed size) then you could try using an iframe.
Alternatively, if you want to save the variables you can either put them in ViewState or SessionState so that they are persisted between postbacks
This is not possible with UpdatePanels... the entire page will go through the entire lifecycle. As others mentioned, you can limit the processing that happens by using IsPostBack or ScriptManager's IsInAsyncPostBack, but ultimately this is not going to be a great solution for complex pages.
However, you can use Page Methods to execute just one static method in your page, but you'll have to make the Javascript call yourself and update the UI. Here are some examples:
http://www.singingeels.com/Articles/Using_Page_Methods_in_ASPNET_AJAX.aspx
http://encosia.com/2009/07/21/simplify-calling-asp-net-ajax-services-from-jquery/
http://weblogs.asp.net/craigshoemaker/archive/2008/09/29/using-jquery-to-call-asp-net-ajax-page-methods.aspx