TreeView in Web Custom Control

J

Jonas

Hi.
I'm trying to develop a web custom control that uses a programmatically
created treeview.
My problem is that I get an exception when I try to render the control.
With properties do I have to assign to get this working.
Here is some sample code:

namespace WebControlLibrary1
{
[ToolboxData("<{0}:MyControl runat=server></{0}:MyControl>")]
public class MyControl : WebControl
{
protected override void RenderContents(HtmlTextWriter output)
{
XmlDataSource source = new XmlDataSource();
source.Data = GetXmlElement().OuterXml;

TreeView tv = new TreeView();
tv.ID = ClientID + "_TreeView";
tv.ImageSet = TreeViewImageSet.XPFileExplorer;
tv.RenderControl(output);
}

private XmlElement GetXmlElement()
{
XmlDocument doc = new XmlDocument();
doc.LoadXml("<Xml><EmptyXml /></Xml>");
return doc.DocumentElement;
}
}
}


Best regards
Jonas Samuelsson
 
J

Jonas

Hi,
here is the exception info:

System.NullReferenceException was unhandled by user code
Message="Object reference not set to an instance of an object."
Source="System.Web"
StackTrace:
at System.Web.UI.Control.get_SpacerImageUrl()
at
System.Web.UI.WebControls.TreeView.RenderBeginTag(HtmlTextWriter
writer)
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at WebControlLibrary1.MyControl.RenderContents(HtmlTextWriter
output) in C:\Work\WebSite1\WebControlLibrary1\MyControl.cs:line 27
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at
System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter
writer)
at
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter
writer)
at System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter
output)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at
System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.Control.Render(HtmlTextWriter writer)
at System.Web.UI.Page.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
 
G

Gaurav Vaish \(EduJini.IN\)

Cryptic only with the exception that SpacerImageUrl is missing.
Provided any value to it?
Or may be something coming out of MyControl.cs

Mail me the relevant code (with aspx) at
gaurav~DOT~vaish[at]gmail~DOT~com... not sure, but probably may be of some
help.
 
P

Prakash V

Hi ,
i too got the same problem, i try to render a treecontrol and pass
the html to some other mehthod, it give object set to null exception, i
tried many things but cannot do it, i tried to replace get_spacerImageurl()
but no use. Did anyone have solution for this problem

part of my code is
private string RenderTree()

{


TreeView Tview = new TreeView();

TreeNode tnode = new TreeNode("Node1", "1");

Tview.Nodes.Add(tnode);

Tview.ID = "Tree1";


StringBuilder sb = new StringBuilder();

StringWriter sw = new StringWriter(sb);

HtmlTextWriter htmlTW = new HtmlTextWriter(sw);

Tview.RenderControl(htmlTW);

return sb.ToString();

}

and stack trace is [NullReferenceException: Object reference not set to an
instance of an object.]
System.Web.UI.Control.get_SpacerImageUrl() +50
System.Web.UI.WebControls.TreeView.RenderBeginTag(HtmlTextWriter writer)
+202
System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +31
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer,
ControlAdapter adapter) +74
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter
adapter) +291
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +49
TreeviewRender.RenderTree() in
d:\TestProject\TestProject\TreeviewRender.aspx.cs:30
TreeviewRender.Page_Load(Object sender, EventArgs e) in
d:\TestProject\TestProject\TreeviewRender.aspx.cs:17
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o,
Object t, EventArgs e) +31
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender,
EventArgs e) +68
System.Web.UI.Control.OnLoad(EventArgs e) +88
System.Web.UI.Control.LoadRecursive() +74
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3030







Gaurav Vaish (EduJini.IN) said:
Cryptic only with the exception that SpacerImageUrl is missing.
Provided any value to it?
Or may be something coming out of MyControl.cs

Mail me the relevant code (with aspx) at
gaurav~DOT~vaish[at]gmail~DOT~com... not sure, but probably may be of some
help.

--
Happy Hacking,
Gaurav Vaish
http://www.mastergaurav.org
http://www.edujini.in
-------------------


Jonas said:
Hi,
here is the exception info:

System.NullReferenceException was unhandled by user code
Message="Object reference not set to an instance of an object."
Source="System.Web"
StackTrace:
at System.Web.UI.Control.get_SpacerImageUrl()
at
System.Web.UI.WebControls.TreeView.RenderBeginTag(HtmlTextWriter
writer)
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at WebControlLibrary1.MyControl.RenderContents(HtmlTextWriter
output) in C:\Work\WebSite1\WebControlLibrary1\MyControl.cs:line 27
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at
System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter
writer)
at
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter
writer)
at System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter
output)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at
System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.Control.Render(HtmlTextWriter writer)
at System.Web.UI.Page.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Click to expand...
Click to expand...
 
G

Gaurav Vaish \(www.EduJini.IN\)

I've given a solution to Jonas...
Just set the value of,... grrr... lost the property name, as empty
value.

BRB :)

--
Happy Hacking,
Gaurav Vaish | http://www.mastergaurav.org
http://www.edujini.in | http://webservices.edujini.in
-------------------


Prakash V said:
Hi ,
i too got the same problem, i try to render a treecontrol and pass
the html to some other mehthod, it give object set to null exception, i
tried many things but cannot do it, i tried to replace
get_spacerImageurl() but no use. Did anyone have solution for this problem

part of my code is
private string RenderTree()

{


TreeView Tview = new TreeView();

TreeNode tnode = new TreeNode("Node1", "1");

Tview.Nodes.Add(tnode);

Tview.ID = "Tree1";


StringBuilder sb = new StringBuilder();

StringWriter sw = new StringWriter(sb);

HtmlTextWriter htmlTW = new HtmlTextWriter(sw);

Tview.RenderControl(htmlTW);

return sb.ToString();

}

and stack trace is [NullReferenceException: Object reference not set to an
instance of an object.]
System.Web.UI.Control.get_SpacerImageUrl() +50
System.Web.UI.WebControls.TreeView.RenderBeginTag(HtmlTextWriter writer)
+202
System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +31
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer,
ControlAdapter adapter) +74
System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter) +291
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +49
TreeviewRender.RenderTree() in
d:\TestProject\TestProject\TreeviewRender.aspx.cs:30
TreeviewRender.Page_Load(Object sender, EventArgs e) in
d:\TestProject\TestProject\TreeviewRender.aspx.cs:17
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o,
Object t, EventArgs e) +31
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender,
EventArgs e) +68
System.Web.UI.Control.OnLoad(EventArgs e) +88
System.Web.UI.Control.LoadRecursive() +74
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3030







Gaurav Vaish (EduJini.IN) said:
Cryptic only with the exception that SpacerImageUrl is missing.
Provided any value to it?
Or may be something coming out of MyControl.cs

Mail me the relevant code (with aspx) at
gaurav~DOT~vaish[at]gmail~DOT~com... not sure, but probably may be of
some help.

--
Happy Hacking,
Gaurav Vaish
http://www.mastergaurav.org
http://www.edujini.in
-------------------


Jonas said:
Hi,
here is the exception info:

System.NullReferenceException was unhandled by user code
Message="Object reference not set to an instance of an object."
Source="System.Web"
StackTrace:
at System.Web.UI.Control.get_SpacerImageUrl()
at
System.Web.UI.WebControls.TreeView.RenderBeginTag(HtmlTextWriter
writer)
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at WebControlLibrary1.MyControl.RenderContents(HtmlTextWriter
output) in C:\Work\WebSite1\WebControlLibrary1\MyControl.cs:line 27
at System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at
System.Web.UI.HtmlControls.HtmlForm.RenderChildren(HtmlTextWriter
writer)
at
System.Web.UI.HtmlControls.HtmlContainerControl.Render(HtmlTextWriter
writer)
at System.Web.UI.HtmlControls.HtmlForm.Render(HtmlTextWriter
output)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at
System.Web.UI.HtmlControls.HtmlForm.RenderControl(HtmlTextWriter
writer)
at System.Web.UI.Control.RenderChildrenInternal(HtmlTextWriter
writer, ICollection children)
at System.Web.UI.Control.RenderChildren(HtmlTextWriter writer)
at System.Web.UI.Control.Render(HtmlTextWriter writer)
at System.Web.UI.Page.Render(HtmlTextWriter writer)
at System.Web.UI.Control.RenderControlInternal(HtmlTextWriter
writer, ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer,
ControlAdapter adapter)
at System.Web.UI.Control.RenderControl(HtmlTextWriter writer)
at System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)
Click to expand...
Click to expand...
Click to expand...
 
J

Jonas

I got it working by adding the following line:
treeview.SkipLinkText = "";
before treeview.RenderControl(writer).

Thanks alot Gaurav!
 
P

Prakash V

Hi,
after adding treeview.SkipLinkText = ""; also it's not working, it now
expects GetImageUrl. i am giving my code and stack trace below.

public partial class TreeviewRender : System.Web.UI.Page

{

protected void Page_Load(object sender, EventArgs e)

{

if (IsPostBack)

RenderTree();

}

private string RenderTree()

{

TreeView Tview = new TreeView();

TreeNode tnode = new TreeNode("Node1", "1");

Tview.Nodes.Add(tnode);

Tview.ID = "Tree1";

Tview.SkipLinkText = "";

StringBuilder sb = new StringBuilder();

StringWriter sw = new StringWriter(sb);

HtmlTextWriter htmlTW = new HtmlTextWriter(sw);

Tview.RenderControl(htmlTW);

return sb.ToString();

}

}


Source Error:


Line 30: StringWriter sw = new StringWriter(sb);
Line 31: HtmlTextWriter htmlTW = new HtmlTextWriter(sw);
Line 32: Tview.RenderControl(htmlTW);
Line 33: return sb.ToString();
Line 34:


Source File: d:\TestProject\TestProject\TreeviewRender.aspx.cs Line: 32

Stack Trace:


[NullReferenceException: Object reference not set to an instance of an
object.]
System.Web.UI.WebControls.TreeView.GetImageUrl(Int32 index) +4107
System.Web.UI.WebControls.TreeNode.Render(HtmlTextWriter writer, Int32
position, Boolean[] isLast, Boolean enabled) +2700
System.Web.UI.WebControls.TreeView.RenderContents(HtmlTextWriter writer)
+294
System.Web.UI.WebControls.WebControl.Render(HtmlTextWriter writer) +43
System.Web.UI.Control.RenderControlInternal(HtmlTextWriter writer,
ControlAdapter adapter) +74
System.Web.UI.Control.RenderControl(HtmlTextWriter writer, ControlAdapter
adapter) +291
System.Web.UI.Control.RenderControl(HtmlTextWriter writer) +49
TreeviewRender.RenderTree() in
d:\TestProject\TestProject\TreeviewRender.aspx.cs:32
TreeviewRender.Page_Load(Object sender, EventArgs e) in
d:\TestProject\TestProject\TreeviewRender.aspx.cs:18
System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o,
Object t, EventArgs e) +31
System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender,
EventArgs e) +68
System.Web.UI.Control.OnLoad(EventArgs e) +88
System.Web.UI.Control.LoadRecursive() +74
System.Web.UI.Page.ProcessRequestMain(Boolean
includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3034



Thanks in Advance,
Prakash.V
 
I

itaisc

Joined
Oct 9, 2007
Messages
2
Reaction score
0
I have a kind of solution...

What I did is to inherit From TreeView and that gave me all the functionalities of Web control and also cause my control to become a control with TreeView that can be rendered properly.

Then when I needed to add some more controls like Text Box and Button I just override the "RenderControl" function and add to it's HtmlTextWriter
my rendered controls.

Hope that it helped you guys!

:congrats:
 

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.

Ask a Question

Similar Threads

TreeView in Custom User Control RenderControl error 0
Treeview control error GetImageUrl 0
"Unknown server tag" problem when creating custom control 0
XML fed Treeview - NULL Reference Exception 2
Web Custom Control Part 2 3
Can't find a GridView inside a template of a custom templated web control 2
Disappearing asp:TreeView in a custom web control 0
Custom control in ASP.NET 1.1.432 issue 0

Members online

Total: 31 (members: 1, guests: 30)
Robots: 450

Forum statistics

Threads
473,770
Messages
2,569,583
Members
45,074
Latest member
StanleyFra

Latest Threads

Top