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Click event on Page_Prerender in C#

In my application there is a grid which gets loaded once the user click on row which has some data, but now my requirement is like I want to load the grid at the time when page gets loaded, so for that I just want to call the Click event to happen automatically at the Page_Prerender itself.
Can anyone please help me out with the solution.

Say you have a grid view like this.
<GridView ID="gvChildGrid" runat="server" />
You can easily data bind it in Page_PreRender event with
protected override void OnPreRender(EventArgs args)
{
gvChildGrid.DataSource = yourdatasource;
gvChildGrid.DataBind();
}

OnCheckedChanged not firing when clicked

I'm trying to run my OnCheckedChanged inside an itemtemplate, but it is not firing. What I did was I typed the OnCheckChanged in the asp:CheckBox tag and also typed the entire method manually. Would this affect the process??
<asp:CheckBox runat="server" ID="uoCheckBoxTagtoVehicle" OnCheckedChanged="ChkChanged" AutoPostBack="true" Width="50px" />
and my event:
protected void ChkChanged(object sender, EventArgs e)
{
uoHiddenFieldVehicle.Value = "1";
}
Note: I'm using Visual studio 2008

Since your control is inside a GridView (since you said ItemTemplate I assume you do) you can't use your approach to attach the event as you did. Because there will be multiple check boxes once you populate the GridView. Therefore, do the following
In you GridView's DataBinding event find the CheckBox by ID (use FindControl method)
Then attach the event OnCheckedChanged to the method you've written

Maybe you are databinding the page also on postback. You should do that only ...
if(!IsPostBack)
{
DataBindPage(); // method which databinds your controls like GridView
}
Otherwise you prevent that events are triggered.

autpostback with textbox in asp.net

I have the following aspx code
<asp:TextBox ID="uname" runat="server" AutoPostBack="True"
ontextchanged="uname_TextChanged"></asp:TextBox>
in code behind file
protected void uname_TextChanged(object sender, EventArgs e)
{
Response.Write("Called on postback");
}
As per my assumption due to autopostback if I write anything in the textbox a postback will occur, but its nor occuring now, what could be the reason?
Normally there are more than 1 event handler for an event like for a control, which event will be triggered if autopostback occurs.?

You said As per my assumption due to autopostback if I write anything in the textbox a postback will occur.
That is wrong. It will fire text changed event when your focus from textbox will be out. So when you type something and press Tab key then only your TextChanged event will be triggered.
If you want to trigger TextChanged event when you type something then you should call it from javascript using OnKeyDown event. see below code sample :
<asp:TextBox ID="uname" runat="server" AutoPostBack="True"
OnKeyDown="TextChanged(this)" OnTextChanged="uname_TextChanged"></asp:TextBox>
<script type="text/javascript">
function TextChanged(control) {
$(control).change();
}
</script>
Now when you type anything in your textbox it will call TextChanged method of javascript and this method will trigger uname_TextChanged event.
Assumption:
If your textbox control is inside UpdatePanel then also your change event cannot be triggered. In such a case you should define trigger for text box. as mentioned below :
<asp:UpdatePanel runat="server" ID="up1">
<ContentTemplate>
<asp:TextBox ID="uname" runat="server" AutoPostBack="True"
OnKeyDown="TextChanged(this)" OnTextChanged="uname_TextChanged"></asp:TextBox>
</ContentTemplate>
<Triggers>
<asp:PostBackTrigger ControlID="uname" />
</Triggers>
</asp:UpdatePanel>
Q : which event will be triggered if autopostback occurs ?
Answer: Normally, for all the events for which contents are changed between the post server, AutoPostBack requires. But it wont be triggered until you define the event for that.
For example if you set the AutoPostBack property of the DropDownList to true, and if you don't specify the OnSelectedIndexChanged event then it will not trigger this event. But your page will be post back when you change the value.
Same thing happens in case of TextBox, CheckBox, RadioButton etc...
Hope it is enough to understand.

Try by changing the ontextchanged to OnTextChanged and try. and after entering the text in textbox try to click the mouse on the page sure it works.

MSDN states that the AutoPostBack is only raised when the control loses focus:
Gets or sets a value that indicates whether an automatic postback to
the server occurs when the TextBox control loses focus.
...
Use the AutoPostBack property to specify whether an automatic postback
to the server will occur when the TextBox control loses focus.
Pressing the ENTER or the TAB key while in the TextBox control is the
most common way to change focus.
However, a test showed that you need to enter a text first for the PostBack to occur. After I entered some text and tabbed out of the TextBox, the PostBack was done and the TextChanged event was raised. After clearing the text and tabbing out of the TextBox, the AutoPostBack was also done, so it does not depend on whether the TextBox is empty or not.
To address also the second part of your question: which event is raised during the PostBack is decided upon by the ASP.NET framework during the initialization phase of the PostBack. E.g. if the text of the TextBox that is contained in the Form values differs from that stored in the ViewState, the TextChanged event is raised. This explains why the TextChanged handler is called even if the AutoPostback was initiated by the losing the focus.

Button click event not firing within use control in ASP .Net

I am developing an asp web page in which I have a drop down combobox and a place holder below that. When the user selects an item from the drop down combobox, a postback is done to the server side and server loads an asp user control to the place holder in this parent page. Everything upto now is working fine.
In the user control I have a button and the user control code behind is implemented to handle the button click event. The problem is, when I click this button, I can see that the postback is send to the server side (i.e. parent page Page_Load() is invoked in debug mode), but both the user control's Page_Load() or button click event handler is not invoked.
Please help..
Some additional information,
My parent page is not an asp master page. Just a simple asp page.
I am using VS2008 and .Net 3.5 SP1 and C#.

You need to ensure that you UserControl exists so the button click event is triggered when viewstate is rebuilt.
Loading your UserControl in the Page_Load will work the first time. When you click the button and the post_back occurs, Page_Load has not occurred yet. This means the UserControl will not exist, which mean the button does not exist for the event to be wired back up. So the UserControl with the button in it cannot be connected to the click event and the click event wont fire.
Recommend that your user control is loaded in this event.
protected override void OnLoad(EventArgs e)
{
base.OnLoad(e);
//-- Create your controls here
}
Try a sandbox test. In page_load, dynamically create a button with a click event in the Page_Load. You will see that the click event does not fire. Now move the button to the OnLoad event. The click event will fire. Also note, the click event will occur before the Page_Load event. Further proof that the button does not exist at the right time.
Another idea...
You are reloading the usercontrol on the page before the button event occurs. Ensure your LoadControl method is inside the If block
if (!IsPostBack)
{
//load usercontrol
}

Default.aspx
<asp:PlaceHolder runat="server" ID="ph1">
</asp:PlaceHolder>
Default.aspx.cs
protected void Page_Load(object sender, EventArgs e)
{
var ctl = LoadControl("Controls/UserControl.ascx");
ph1.Controls.Add(ctl);
}
UserControl.ascx
<h3>User control</h3>
<asp:Button ID="btn1" runat="server" OnClick="btn1_Click" Text ="Click me" />
UserControl.ascx.cs
protected void btn1_Click(object s, EventArgs e)
{
Response.Write("You clicked me, yay");
}
All works like a charm. I see the "You clicked me, yay" written when I click the button
Point of attention. If you try to load the controls dynamically in your example in the handler for SelectedItemChanged event of the dropdown control, it will fail, because of the way that lifecycle works for ASP.Net page.
Instead you should handle such control creation in the PageLoad event of the page, like this example below
Default.aspx
<asp:DropDownList ID="ddl1" runat="server" AutoPostBack="true">
<asp:ListItem Value="0" Text="--select a value--" />
<asp:ListItem Value="1" Text="User control 1" />
<asp:ListItem Value="2" Text="User control 2" />
</asp:DropDownList>
<asp:PlaceHolder runat="server" ID="ph1">
</asp:PlaceHolder>
Default.aspx.cs
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
switch (ddl1.SelectedValue)
{
case "1":
var ctl = LoadControl("Controls/UserControl.ascx");
ph1.Controls.Add(ctl);
break;
case "2":
ctl = LoadControl("Controls/UserControl2.ascx");
ph1.Controls.Add(ctl);
break;
}
}
}

In my particular case, I found that the problem was the UserControl ID (or rather the lack of).
When the UserControl was first instantiated, my button ID was ctl00$ctl02$btnContinue, but after the postback it had changed to ctl00$ctl03$btnContinue, therefore the button event handler didn't fire.
I instead added my UserControl with a fixed ID and the button now always loads with the ID ctl00$myUserControl$btnContinue.

OnCheckedChanged event not firing in GridView at all

I have a GridView with an asp CheckBox in a TemplateField. The TemplateField is defined as follows:
<asp:TemplateField HeaderText="HeaderName">
<ItemTemplate>
<asp:CheckBox ID="checkBoxId" runat="server" OnCheckedChanged="MyCheckChangedMethod" AutoPostBack="true"/>
</ItemTemplate>
</asp:TemplateField>
When I run my web project with a breakpoint inside MyCheckChangedMethod and click the checkbox nothing happens. The breakpoint is not hit. My Visual Studio debugger is running.
Additionally, I have AutoEventWireup = True in my page defnition so I don't have to manually hook up the event. I have never had a problem doing it this way before. I have a button on the same page setup the exact same way with a click event and the breakpoint gets hit fine in that.
Any ideas?

The problem occurs when DataBind is called before the control event is firing.
If you call DataBind in Page_Load put it in
if (!isPostBack) {} and call DataBind in the event handler itself.

You need to add AutoPostback = True in asp:CheckBox tag.

The postback event for the checkbox control won't fire correctly because it's within a GridView that mangles the ID of the control.
If you need the Checkbox to reflect data you can use the CheckBoxField object and bind that way.
If you need it perform an action for the row, you may want to look at the ButtonField object using the CommandName property and the RowCommand event.
There are ways to access the checkboxes within the GridView server side.

try:
<asp:CheckBox ID="checkBoxId" runat="server" AutoPostBack=true OnCheckedChanged="MyCheckChangedMethod"/>
Make sure that the aspx page has CodeFile="YOUR_FILE.aspx.cs" at the top.
Also see to it that your function MyCheckChangedMethod is defined as
Function should have object sender, EventArgs e.
public void MyCheckChangedMethod(object sender, EventArgs e)
{
bool b = false;//your data here
}
Also make sure that the web.config has debug set to true (think already done).