Develop Reference

Artificially firing Page Events in ASP.NET?

I'm working with a static class in C#, and am trying to use Control.RenderControl() to get a string / mark-up representation of a Control.
Unfortunately the control (and all child controls) use event bubbling to populate certain values, for example, when instantiating, then calling RenderControl() on the following:
public class MyTest : Control
{
protected override void OnLoad(EventArgs e)
{
this.Controls.Add(new LiteralControl("TEST"));
base.OnLoad(e);
}
}
I am returned an empty string, because OnLoad() is never fired.
Is there a way I can invoke a 'fake' page lifecycle? Perhaps use some dummy Page control?

I was able to accomplish this by using a local instance of Page and HttpServerUtility.Execute:
// Declare a local instance of a Page and add your control to it
var page = new Page();
var control = new MyTest();
page.Controls.Add(control);
var sw = new StringWriter();
// Execute the page, which will run the lifecycle
HttpContext.Current.Server.Execute(page, sw, false);
// Get the output of your control
var output = sw.ToString();
EDIT
If you need the control to exist inside a <form /> tag, then simply add an HtmlForm to the page, and add your control to that form like so:
// Declare a local instance of a Page and add your control to it
var page = new Page();
var control = new MyTest();
// Add your control to an HTML form
var form = new HtmlForm();
form.Controls.Add(control);
// Add the form to the page
page.Controls.Add(form);
var sw = new StringWriter();
// Execute the page, which will in turn run the lifecycle
HttpContext.Current.Server.Execute(page, sw, false);
// Get the output of the control and the form that wraps it
var output = sw.ToString();

Loading a user control dynamically

I'm trying to load a user control in a web service, but it doesn't execute the Load_Page().
I tried to use:
HttpContext.Current.Server.Execute(page, text, false);
But it returns a NullException. It is my code:
public string Controle(string url)
{
Page page = new Page();
UserControl userControl = (UserControl)page.LoadControl(url);
//userControl.EnableViewState = false;
HtmlForm form = new HtmlForm();
form.Controls.Add(userControl);
page.Controls.Add(form);
StringWriter text = new StringWriter();
HtmlTextWriter htmltext = new HtmlTextWriter(text);
userControl.RenderControl(htmltext);
return text.ToString();
}
Hope it is clear.

You need to initialize the control using a method that does something like
this.Load += Page_Load;
Please refer to this post which explains exactly what needs to be done to achieve this. Be sure to read the section stating; "One word of caution:"
http://weblogs.asp.net/srkirkland/archive/2007/11/05/dynamically-render-a-web-user-control.aspx
This related post will also be able to assist:
Page_Load not firing in UserControl

How call GetWebResourceUrl() when Page is null ?

I built custom ASP.NET control and it's working fine when I add it manually (drag and drop) or by code to controls in markup.
The custom control, MsgBox, had resources like JavaScript, CSS and images embedded in and the problem appeared when I tried to Render the control in class to return its HTML code, the Page instance is null and the "GetWebResourceUrl" needs it:
Page.ClientScript.GetWebResourceUrl(.....)
is there any way to get the resourceurl ? Here is my render code:
protected override void RenderContents(HtmlTextWriter writer)
{
using (PlaceHolder plh = new PlaceHolder())
{
if (Page != null)
{
if (DesignMode || Page.Header == null)
RegisterCSSInclude(plh);
}
HtmlGenericControl container = new HtmlGenericControl("div");
container.EnableViewState = false;
container.InnerHtml = "Control html code";
plh.Controls.Add(container);
plh.RenderControl(writer);
}
}
RegisterCSSInclude is method to register my css files:
private void RegisterCSSInclude(Control target)
{
// CSS
bool linkIncluded = false;
foreach (Control c in target.Controls)
{
if (c.ID == "MsgBxStyle")
{
linkIncluded = true;
}
}
if (!linkIncluded)
{
HtmlGenericControl globalCsslink = new HtmlGenericControl("link");
globalCsslink.ID = "MsgBxGStyle";
globalCsslink.Attributes.Add("href", Page.ClientScript.GetWebResourceUrl(typeof(MessageBoxCtrl), "MessageBox.MsgBxStyles.WeDevMsgBox.css"));
globalCsslink.Attributes.Add("type", "text/css");
globalCsslink.Attributes.Add("rel", "stylesheet");
globalCsslink.EnableViewState = false;
target.Controls.Add(globalCsslink);
HtmlGenericControl csslink = new HtmlGenericControl("link");
csslink.ID = "MsgBxStyle";
csslink.Attributes.Add("href", Page.ClientScript.GetWebResourceUrl(typeof(MessageBoxCtrl), "MessageBox.MsgBxStyles." + Style.ToString().ToLower() + ".css"));
csslink.Attributes.Add("type", "text/css");
csslink.Attributes.Add("rel", "stylesheet");
csslink.EnableViewState = false;
target.Controls.Add(csslink);
}
}
Update:
PS: I'm tring to use control in generic handler (ashx) where I call ShowMsgBox method which is a method in a class and not in a page or user control.
ShowMsgBox method should create an instance of MsgBox control and render it then return the html code to ashx class :
var htmlCode = MyClass.ShowMsgBox("myMsg");
context.Response.write(htmlCode);

I built a custom ASP.NET control ...
I'm tring to use control in generic handler (ashx) ... not in a page or user control.
A Page is a handler. You want to use a convenience provided by the Page class, but you don't want to inherit from Page. The niceties of Page, such as ClientScript, expect a Page from which to get various information.
You can provide a dummy Page object to your control by setting the Page property of your custom Control:
this.Page = new Page();
...then you will need to set various properties (assuming they are public) which are expected by ClientScriptManager.GetWebResourceUrl():
this.Page.Foo = "bar";
then you can call:
this.Page.ClientScript.GetWebResourceUrl(...);

If this is the specific class that inherits from WebControl page shouldn't be null. If its another class that you are rendering as part of a hierarchy you can add a parameter of type Page and pass the reference of the current page to it.

Control 'ctl02' of type 'Button' must be placed inside a form tag with runat=server

I get that error when trying to generate a number of buttons programmatically. I have no ctl02.. Why do i get that mistake?
Button pgs = new Button();//Create New Topic
pgs.Width = 20;
pgs.Command += obtainTopicsPerPage_Click;
pgs.CommandName = tPage.ToString();
pgs.Text = tPage.ToString();
btns.Add(tPage.ToString());
buttons.Add(pgs);
I create a few buttons and loop through the list (buttons). Then i get that mistake :(. ... why?
Full design:
int maximumTopicPages;
int tPage;
int questionNumber=1;
Dictionary<string, List<DisplayAllQuestionsTable>> tPages;
List<Button> buttons = new List<Button>();
protected void Answer_Click(object sender, EventArgs e)
{
ViewState["SeekPressed"] = "pressed";
tPages = new Dictionary<string, List<DisplayAllQuestionsTable>>();
string subTopic = SubTopicDropDownList.SelectedItem.Value;
List<DisplayAllQuestionsTable> threadsByTopic = new List<DisplayAllQuestionsTable>();
List<string> btns = new List<string>();
foreach (var topicKeys in postsByTopic)
{
if (topicKeys.Key == subTopic)
{
foreach (var item in postsByTopic[topicKeys.Key])
{
questionNumber++;
maximumTopicPages++;
threadsByTopic.Add(item);//Adds All DisplayAllTables objects
//if there are 20 add a button.
if (maximumTopicPages == 20)
{
tPages.Add(tPage++.ToString(), threadsByTopic);//Add a number to the page each time, with a DisplayTable object
//new Button
Button pgs = new Button();//Create New Topic
pgs.Width = 20;
pgs.Command += obtainTopicsPerPage_Click;
pgs.CommandName = tPage.ToString();
pgs.Text = tPage.ToString();
btns.Add(tPage.ToString());
buttons.Add(pgs);
maximumTopicPages = 0;
threadsByTopic.Clear();
}
}//number of questions per page
if (!tPages.ContainsKey((questionNumber / 20).ToString()))
{
tPages.Add((questionNumber / 20).ToString(), threadsByTopic);//If A button is missing add it.
}
}
Way the buttons are added to the table:
void MyButtonTable()
{
TableRow myTableRow = new TableRow();
HtmlForm form = new HtmlForm();
form.Attributes.Add("runat", "server");
Page.Controls.Add(form);
foreach (var item in buttons)
{
TableCell myTableCell = new TableCell();
form.Controls.Add(item);
myTableCell.Controls.Add(item);
myTableRow.Cells.Add(myTableCell);
}
Table2.Rows.Add(myTableRow);
Page.Controls.Add(Table2);
}

Are you adding your buttons to the Page afterwards?
Also, if you do not specify an ID to your buttons, they will be given one automatically in the form of ctlXXX

What is in the .aspx file? Specifically, what is the 'buttons' control? My guess is, it is a placeholder or panel or something similar. In that case, you need to add this to your .aspx file:
...
<body>
<form runat="server">
...
</form>
</body>
...
That should fix it.
ASP.NET needs to have the <form> tag managed by the server in order to use server side controls on your page. If your page already has a <form> tag on it somewhere, you can just add runat="server" to that tag and it will fix it. (That assumes the 'buttons' control that you're trying to add the dynamically created button into -- the placeholder or panel or whatever -- is itself between the <form>...</form> tags.)

Its working....
Please add your new button control into from
protected void btnsubmit_Click(object sender, EventArgs e)
{
Button objButton = new Button();
objButton.Text = "New Button";
objButton.ID = "randomButton";
form1.Controls.Add(objButton);
}
Here form1 -> form name available into .aspx file and objButton is button object.

You have to check if "buttons" (I think is a placeholder) is inside a div or a tag with runat="server"
update
If I understand you can try something like this:
HtmlForm form = new HtmlForm();
form.Attributes.Add("runat", "server");
form.Controls.Add(buttons);
Page.Controls.Add(form);
(untested)

GridView must be placed inside a form tag with runat="server" even after the GridView is within a form tag

<form runat="server" id="f1">
<div runat="server" id="d">
grid view:
<asp:GridView runat="server" ID="g">
</asp:GridView>
</div>
<asp:TextBox runat="server" ID="t" TextMode="MultiLine" Rows="20" Columns="50"></asp:TextBox>
</form>
Code behind:
public partial class ScriptTest : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
g.DataSource = new string[] { "a", "b", "c" };
g.DataBind();
TextWriter tw = new StringWriter();
HtmlTextWriter h = new HtmlTextWriter(tw);
d.RenderControl(h);
t.Text = tw.ToString();
}
}
Even the GridView is within a from tag with runat="server", still I am getting this error.
Any clues please ?

You are calling GridView.RenderControl(htmlTextWriter), hence the page raises an exception that a Server-Control was rendered outside of a Form.
You could avoid this execption by overriding VerifyRenderingInServerForm
public override void VerifyRenderingInServerForm(Control control)
{
/* Confirms that an HtmlForm control is rendered for the specified ASP.NET
server control at run time. */
}
See here and here.

An alternative to overriding VerifyRenderingInServerForm is to remove the grid from the controls collection while you do the render, and then add it back when you are finished before the page loads. This is helpful if you want to have some generic helper method to get grid html because you don't have to remember to add the override.
Control parent = grid.Parent;
int GridIndex = 0;
if (parent != null)
{
GridIndex = parent.Controls.IndexOf(grid);
parent.Controls.Remove(grid);
}
grid.RenderControl(hw);
if (parent != null)
{
parent.Controls.AddAt(GridIndex, grid);
}
Another alternative to avoid the override is to do this:
grid.RenderBeginTag(hw);
grid.HeaderRow.RenderControl(hw);
foreach (GridViewRow row in grid.Rows)
{
row.RenderControl(hw);
}
grid.FooterRow.RenderControl(hw);
grid.RenderEndTag(hw);

Just after your Page_Load add this:
public override void VerifyRenderingInServerForm(Control control)
{
//base.VerifyRenderingInServerForm(control);
}
Note that I don't do anything in the function.
EDIT: Tim answered the same thing. :)
You can also find the answer Here

Just want to add another way of doing this. I've seen multiple people on various related threads ask if you can use VerifyRenderingInServerForm without adding it to the parent page.
You actually can do this but it's a bit of a bodge.
First off create a new Page class which looks something like the following:
public partial class NoRenderPage : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{ }
public override void VerifyRenderingInServerForm(Control control)
{
//Allows for printing
}
public override bool EnableEventValidation
{
get { return false; }
set { /*Do nothing*/ }
}
}
Does not need to have an .ASPX associated with it.
Then in the control you wish to render you can do something like the following.
StringWriter tw = new StringWriter();
HtmlTextWriter hw = new HtmlTextWriter(tw);
var page = new NoRenderPage();
page.DesignerInitialize();
var form = new HtmlForm();
page.Controls.Add(form);
form.Controls.Add(pnl);
controlToRender.RenderControl(hw);
Now you've got your original control rendered as HTML. If you need to, add the control back into it's original position. You now have the HTML rendered, the page as normal and no changes to the page itself.

Here is My Code
protected void btnExcel_Click(object sender, ImageClickEventArgs e)
{
if (gvDetail.Rows.Count > 0)
{
System.IO.StringWriter stringWrite1 = new System.IO.StringWriter();
System.Web.UI.HtmlTextWriter htmlWrite1 = new HtmlTextWriter(stringWrite1);
gvDetail.RenderControl(htmlWrite1);
gvDetail.AllowPaging = false;
Search();
sh.ExportToExcel(gvDetail, "Report");
}
}
public override void VerifyRenderingInServerForm(Control control)
{
/* Confirms that an HtmlForm control is rendered for the specified ASP.NET
server control at run time. */
}

Tim Schmelter's answer helped me a lot, but I had to do one more thing to get it to work on my aspx page. I am using this code to email an embedded GridView control (as HTML), for report automation.
In addition to adding the override sub, I had to do the render() in Me.Handles.onunload, or else I got an error on the RenderControl line.
Protected Sub Page_After_load(sender As Object, e As EventArgs) Handles Me.Unload
If runningScheduledReport Then
Dim stringBuilder As StringBuilder = New StringBuilder()
Dim stringWriter As System.IO.StringWriter = New System.IO.StringWriter(stringBuilder)
Dim htmlWriter As HtmlTextWriter = New HtmlTextWriter(stringWriter)
GridView1.RenderControl(htmlWriter)
Dim htmlcode As String = stringBuilder.ToString()
Func.SendEmail(Context.Request.QueryString("email").ToString, htmlcode, "Auto Report - Agent Efficiency", Nothing)
End If
End Sub