Develop Reference

Use of Page_PreRender to execute C# code when page controls are loaded

I have the following code :
protected void Page_Load(object sender, EventArgs e)
{
string runat = "runat=\"server\"";
}
protected void Page_PreRender(object sender, EventArgs e)
{
//some code
}
<iframe <%=runat%>></iframe>
I need to be sure the code within Page_PreRender executes only when the variable runat has been initialized & the iframe control is ready for rendering.
Unfortunately it does not work. I also tried Page_PreRenderComplete and it does not work.
Does anyone have an idea to fix this problem ?
Thanks!

Create a PlaceHolder in your markup and then add the iframe programmatically to the PlaceHolder as a LiteralControl, like this:
protected void Page_Load(object sender, EventArgs e)
{
PlaceHolder1.Controls.Add(new LiteralControl("<iframe src='something.aspx'></iframe>"));
}

Textbox to label with two websites

I have two sites in one of them i have a textbox and on the other site i have a label. What i want to do is have the value that is written in the textbox be passed on to the label in the next website on a button click.
Website1.aspx (with the textbox)
protected void btnSpara_Click(object sender, EventArgs e)
{
}
The textbox:
<asp:TextBox ID="tbxKommentar" runat="server" OnTextChanged="tbxKommentar_TextChanged"></asp:TextBox>
Website2.aspx (with the label)
<asp:Label ID="lblKommentar" runat="server"></asp:Label>
How would i go about doing this.

So what you are asking is how to pass value from one page to another. There are several options and all of them are described here https://msdn.microsoft.com/en-us/library/6c3yckfw.aspx
Code sample:
protected void btnSpara_Click(object sender, EventArgs e)
{
Response.Redirect("Website2.aspx?txt="+ tbxKommentar.Text);
}
In your Website2.aspx:
protected override void OnInit(EventArgs e){
lblKommentar.Text = Request.Params["txt"];
}

How do capture row selected in gridview and pass username value to text box in the next page?

I would like to select the gridview and redirect to the next page where username in gridview passed to the text box in the next page when the row is being clicked. How do i do that?
My code behind (on the first page):
protected void GridView1_OnRowSelected(object sender, GridViewSelectEventArgs e)
{
var username = Convert.ToString(GridView1.DataKeys[e.NewSelectedIndex].Value);
Response.Redirect("ViewUploads.aspx?USERNAME=" +username);
}
My code on the second page:
protected void TextBoxUsername_TextChanged(object sender, EventArgs e)
{
var username = Request.QueryString["USERNAME"];
}

I assume that you're looking for the SelectedIndexChanged event of the GridView.
protected void GridView_SelectedIndexChanging(Object sender, GridViewSelectEventArgs e)
{
var username = GridView1.DataKeys[e.NewSelectedIndex].Value.ToString();
Response.Redirect("ViewUploads.aspx?USERNAME=" +username);
}
In the next page(ViewUploads.aspx) you need to assign it to the TextBox' Text:
protected void Page_Load(object sender, EventArgs e)
{
if(!IsPostBack && Request.QueryString["USERNAME"] != null)
this.txtUserName.Text = Request.QueryString["USERNAME"];
}
I'm not sure if you have already done that, if you want to use the DataKeys-collection in the first page, you have to set the DataKeyNames property accordingly. For example:
<asp:gridview id="GridView1"
datakeynames="UserName"
onselectedindexchanged="GridView_SelectedIndexChanging"
runat="server">
...
</asp:gridview>

The RowDataBound events of the gridview is not fired after turning to the next page

I use a gridview to display the search result. After clicking search button, the gridview will show page 1, but when I click page 2 link, the gridview disappeared and it was back when I click search button again and show page 2's content.
here is my code
<asp:GridView ID="searchresult" runat="server" AutoGenerateColumns="true" AllowPaging="true" OnRowDataBound="searchresult_RowDataBound" OnPageIndexChanging="searchresult_PageIndexChanging"
HeaderStyle-BackColor="#f9e4d0"
HeaderStyle-Height="20px"
Font-Size="11px"
AlternatingRowStyle-BackColor="#cfdfef"
Width="800px" style="text-align:left">
</asp:GridView>
and code behind
protected void search_Click(object sender, EventArgs e)
{
List<someclass> totalResult = new List<someclass>();
..... //some code to generate the datasource
searchresult.DataSource = totalResult;
searchresult.AllowPaging = true;
searchresult.DataBind();
}
protected void searchresult_RowDataBound(object sender, GridViewRowEventArgs e)
{
}
protected void searchresult_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
searchresult.PageIndex = e.NewPageIndex;
DataBind();
}
I have no idea why the page 2 won't show up until I click search button again. when I clicked the page 2 link, the page did postback but the RowDataBound event was not fired

You have to give your grid a datasource. It appears you are only doing this on search_Click, so your grid is only going to have data then. Try something like:
protected void search_Click(object sender, EventArgs e)
{
PopGrid();
}
protected void searchresult_PageIndexChanging(object sender, GridViewPageEventArgs e)
{
searchresult.PageIndex = e.NewPageIndex;
PopGrid();
}
protected void PopGrid()
{
List<someclass> totalResult = new List<someclass>();
..... //some code to generate the datasource
searchresult.DataSource = totalResult;
searchresult.AllowPaging = true;
searchresult.DataBind();
}

searchresult_PageIndexChanging event handler will make that functionality work. However I recommend you use a gridview control inside a Panel with vertical scroll bar. My user love it and it is a lot faster moving up and down the gridview without defining any page index changing.
I hope it work for you.

Run the button event handler before page_load

I have a table with all the objects I have in my db. I load them in my Page_Load function. I have a text field and a button that when clicking the button, I want the handler of that click to put a new object with the name written in the text field in the db.
Now, I want that what happens after the click is that the page loads again with the new item in the table. The problem is that the button event handler is run after the Page_Load function.
A solution to this would be to use IsPostBack in the Page_Load or use the pre load function. A problem is that if I would have 3 different buttons, I would have to differ between them there instead of having 3 different convenient functions.
Any solutions that don't have this problem?
Code:
protected void Page_Load(object sender, EventArgs e)
{
if (Session["userId"] == null)
Response.Redirect("Login.aspx");
// LOAD DATA FROM DB
}
protected void CreateObject(object sender, EventArgs e)
{
// SAVE THE NEW OBJECT
}

Maybe you should try loading your data during PreRender instead of Load
protected void Page_Load(object sender, EventArgs e)
{
this.PreRender += Page_PreRender
if (Session["userId"] == null)
Response.Redirect("Login.aspx");
}
protected bool reloadNeeded {get; set;}
protected void CreateObject(object sender, EventArgs e)
{
// SAVE THE NEW OBJECT
reloadNeeded = true;
}
protected void Page_PreRender(object sender, EventArgs e)
{
if(reloadNeeded || !IsPostBack)
// LOAD DATA FROM DB
}

You can check the event target and do what you need then:
protected void Page_Load(object sender, EventArgs e)
{
if (IsPostBack)
{
string eventTarget = Page.Request.Params["__EVENTTARGET"];
if(whatever)
{
//do your logic here
}
}
}
Get control name in Page_Load event which make the post back

Use the Page_PreRenderComplete event to retrieve your table. That way your page will always have the most recent data available after all user events have fired.

Why don't you move what you have in the click event into a new method. Then call that method as the first line in your page load?

An old question but I faced the same problem in my C#/ASP.NET Website with master/content pages: a click on a link on the master page should change a query parameter for a gridview on the content page. As you stated the button click event is handled after Page_Load. But it is handled before Page_LoadComplete (see the information about ASP.NET Page Life Cycle), so you can change the page content there.
In my case I solved the problem by setting a session variable in the click event in the master page, getting this variable in the Page_LoadComplete event in the content page and doing databind based on that.
Master page:
<asp:LinkButton ID="Btn1" runat="server" OnCommand="LinkCommand" CommandArgument="1" >Action 1</asp:LinkButton>
<asp:LinkButton ID="Btn2" runat="server" OnCommand="LinkCommand" CommandArgument="2" >Action 2</asp:LinkButton>
protected void LinkCommand(object sender, CommandEventArgs e)
{
HttpContext.Current.Session["BindInfo", e.CommandArgument.ToString());
}
Content page:
protected void Page_LoadComplete(object sender, EventArgs e)
{
string BindInfo = HttpContext.Current.Session["BindInfo"].ToString();
YourBindDataFunction(BindInfo);
}