Casting to a derived TreeNode object (from a TreeViewEventAr gs Node)

[Andrew]

created a custom class that is derived from TreeNode, let's call it
customTreeNode. I'm trying to use the TreeViewEventAr gs (for the
AfterSelect event) but I cannot cast to my derived TreeNode. Here is
a snip...

---code snip---
private void _TreeView_After Select(object sender, TreeViewEventAr gs e)
{
customTreeNode foo = (customTreeNode )e.Node;
displayInfo(foo );
}

private void displayInfo(cus tomTreeNode cTreeNode) {
//code
}
---code snip---

Following the example from MSDN,
(http://msdn.microsoft.com/library/de...-us/vbcon/html
/vbtsksubclassin glistitemortree node.asp),
the MSDN example (at the bottom of the page) is almost exactly like
the above code.

At runtime, I get a InvalidCastExce ption. What gives?

In the AfterSelect event handler method, if I do
'e.Node.GetType ()'--it is, in fact, a customTreeNode. If I do not
attempt to cast to a customTreeNode and just try to pass it to
displayInfo, I get a compilation error because the compiler thinks
that e.Node is TreeNode, not a customTreeNode (expected).

Am I casting incorrectly? Is this a bug? Is the documentation shoddy?

Thanks,
Andrew

[Jon Skeet]

Andrew <ac*********@ph erret.com> wrote:

<snip>

At runtime, I get a InvalidCastExce ption. What gives?

In the AfterSelect event handler method, if I do
'e.Node.GetType ()'--it is, in fact, a customTreeNode. If I do not
attempt to cast to a customTreeNode and just try to pass it to
displayInfo, I get a compilation error because the compiler thinks
that e.Node is TreeNode, not a customTreeNode (expected).

Am I casting incorrectly? Is this a bug? Is the documentation shoddy?

Are you loading the custom nodes via reflection by any chance? Many
cast errors which look like they shouldn't happen is because you're
trying to cast an instance of one type to another type with the same
name, but from a different assembly.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too

[Andrew]

> Are you loading the custom nodes via reflection by any chance? Many

cast errors which look like they shouldn't happen is because you're
trying to cast an instance of one type to another type with the same
name, but from a different assembly.

Not sure what you mean by 'loading'. But, I load the nodes via the Add
method:
myTreeView.Node s.Add(my_custom TreeNode);

Add my customTreeNode class looks like this:

---customTreeNode class---

public customTreeNode : TreeNode {
private customData _myData;

public customTreeNode( customData myData) : base(myData.nam e,
(int)myData.sta tus, (int)myData.sta tus) { //to init a TreeNode with
different images based on the status
_myData = myData;
}

--end--

[Jon Skeet]

Andrew <ac*********@ph erret.com> wrote:

Are you loading the custom nodes via reflection by any chance? Many
cast errors which look like they shouldn't happen is because you're
trying to cast an instance of one type to another type with the same
name, but from a different assembly.

Not sure what you mean by 'loading'. But, I load the nodes via the Add
method:
myTreeView.Node s.Add(my_custom TreeNode);

Add my customTreeNode class looks like this:

---customTreeNode class---

public customTreeNode : TreeNode {
private customData _myData;

public customTreeNode( customData myData) : base(myData.nam e,
(int)myData.sta tus, (int)myData.sta tus) { //to init a TreeNode with
different images based on the status
_myData = myData;
}

Hmmm - that should be fine then. What happens if you do:

Console.WriteLi ne (e.Node.GetType ()==typeof(cust omTreeNode));

?

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too

[Andrew]

> Hmmm - that should be fine then. What happens if you do:

Console.WriteLi ne (e.Node.GetType ()==typeof(cust omTreeNode));

?

It returns false;

[Jon Skeet]

[Please don't mail me and post at the same time - it only confuses
things.]

Andrew <ac*********@ph erret.com> wrote:

Hmmm - that should be fine then. What happens if you do:

Console.WriteLi ne (e.Node.GetType ()==typeof(cust omTreeNode));

?

It returns false;

Right. In that case, check:

o The name (I think you've done this already)
o The assembly each type was loaded from, in terms of filename
o The assembly each type was loaded from, in terms of object reference

Can you provide a short but complete piece of code which demonstrates
the problem (and nothing else)?

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too

[Chris Hornberger]

Your cast looks good. I use descendants of ListViewItems all the time.
Just got done working on one where ListViewMDBItem descended from
ListViewItem and contained all kinds of interesting tidbits about the
schema in the MDB file as well as the FullName to the mdb file. I've
done bunches of things like this and not had any problem, as long as
I'm watchful of the casts.

What he meant by "loading" your objects via reflection is if you were
sucking them from a DLL at runtime using the activator class. It
sounds like you're not so that problem isn't relavent here. Your code
should run fine.

Am I casting incorrectly? Is this a bug? Is the documentation shoddy?

Thanks,
Andrew

[Jon Skeet]

Andrew <ac*********@ph erret.com> wrote:

Right. In that case, check:

o The name (I think you've done this already)
o The assembly each type was loaded from, in terms of filename
o The assembly each type was loaded from, in terms of object reference

Can you provide a short but complete piece of code which demonstrates
the problem (and nothing else)?

Yes, I attached the code. I tried to make it as short as possible.

<snip>

On my box that immediately bails out - and e.Node is *not* a
customTreeNode, it's a plain System.Windows. Forms.TreeNode.

That's because the "mommy" node (which is initially selected) is a
plain TreeNode. Changing the code for treeView1_After Select to:

private void treeView1_After Select(object sender,
System.Windows. Forms.TreeViewE ventArgs e)
{
if (e.Node is customTreeNode)
{
customTreeNode cNode = (customTreeNode )e.Node;
this.textBox1.T ext = cNode.myData;
}
}

it changes the text when I click on a child node, but not otherwise.

Given what you said previously about e.Node actually *being* a
customTreeNode when it's failing, I don't think I'm seeing the actual
problem here.

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet/
If replying to the group, please do not mail me too