Problem is: Sometimes you can use a parameter to assign it to the Value property of an object (e.g. of a TreeView Node ), sometimes you can't.
When it does not work you get an error message like "cannot convert [...].String to System.Windows.Forms.TreeView"
Funny thing is: In most cases it works directly at the beginning of a sub. It never (?) works further down in the body of a sub.
Following example sub ist not working (assume TempNode is a TreeView node which has been initialized):
[I have tried several variants]
' parameter ile is a file opened with FileOpen for writing
' node is a TreeView node object
Sub RecursiveWrite (file, node)
' First use of node sometimes works
TempNode.Value = node ' Remark: or node.value, try both
FileWrite(file, TempNode.text)
nodeCount = TempNode.Count - 1
for i = 0 to nodeCount
RecursiveWrite(file, TempNode.GetNode(i))
' or:
' TempNode.Value = TempNode.GetNode(i)
' RecursiveWrite(file, TempNode.Value)
' Reset TempNode, never works
TempNode.Value = node ' or node.value, does not matter :-(
node
End Sub
Yes, you are right, it should also be .value on the right hand side of the "="
I am sure that it is not an empty node. Especially I had the case that within one call the first use worked and the second not, although I did not change 'node' within one call.
It might be the cause that recursion is the real problem. In general, if you do recursive calls I expect a stack of local parameters and variables. Is this expectation correct fpr B4PPC?
Unfortunaley I just overwrote my whole code with save as (desaster is one short click away :-( ), otherwise i could send you the complete thing. [I do not assume it is possible to decompile B4PPC-Programs]
To prevent further theoretical discussions, I just coded some fully working example (see below, you can use copy&paste).
You need
Form1 : Form
Component added : TreeView.dll
Tree: TreeView
Node, TempNode: Node
---
Here's the error message:
An error occured on sub recursivedescent
Line numer: 70
TempNode.Value = nodeAsParameter
Error description:
Das Object mit dem Typ System.Int32 kann nicht in den Typ Systems.Windows.Forms.TreeNode konvertiert werden.
Continue?
[Buttons Yes/No]
Translation of error:
The object with type System.Int32 cannot be converted to type Systems.Windows.Forms.TreeNode.
---
Heres the sample code:
-- 8< -- snip -
Sub Globals
'Declare the global variables here.
Dim Result
End Sub
' Initialize node for recursive call
Node.Value = Tree.GetNode(0)
' No recursion: Works fine!
UseNode(Node.Value)
' Recursice Call
RecursiveDescent(Node.Value)
' Use result
Msgbox(Result,"Result")
End Sub
Sub UseNode(nodeAsParameter)
' Assign Temp Node
TempNode.Value = nodeAsParameter
' Sample use
Msgbox(TempNode.Text, "It Works")
TempNode.Text = "New name"
Msgbox(TempNode.Text, "It Still Works")
End Sub
Sub RecursiveDescent(nodeAsParameter)
' Assign Temp Node (works!)
TempNode.Value = nodeAsParameter
Msgbox(TempNode.Text, "It Works in First Line")
' Do something for each node:
Result = Result & TempNode.Text & crlf
nodeCount = TempNode.Count - 1
For i = 0 To nodeCount
' This will overwrite TempNode
TempNode.Value = TempNode.GetNode(i)
RecursiveDescent(TempNode.Value)
' Reset TempNode after recursion (does not work!!!)
' Exactly the same as in first line of sub!
TempNode.Value = nodeAsParameter
Next
End Sub
1. Why does the first line of my recursive function work then?
2. Using the name of the object won't help for the recursion - it is essential to be able to re-assign the original reference
3. As a workaround I think it should be possible to implement something similar to the iterators known form C# or Java. As soon as I have some code I'm gonna post it in the correct Main Category (Code Samples)
Last edited by Woinowski : 08-28-2007 at 03:39 PM.
1. In a nutshell, Basic4ppc remembers the last object value returned and then it uses it the next time an object is required. Again you should not pass objects to subs as it will not work consistently.
2. Why won't it work? I think it should work properly.
2. Why won't it work? I think it should work properly.
I see his problem (I think). There is only a single TempNode in the scope of the recursion, whereas he needs a different local node reference for each level of descent because he is recursing in a loop and needs the original reference to identify the next node to recurse into.
When you do "Node.AddNewNode("Level 1.1")" what is the name of the added node or is it anonymous? Is there any way of saving a node reference in a local variable -I've tried it and it doesn't error but also doesn't work!
Sub Globals 'Declare the global variables here. Dim Result End Sub
Sub App_Start form1.Show Tree.New1("Form1", 0, 0, 200,200) Tree.AddNewNode("Root") Node.New1 Node.Value = Tree.GetNode(0) Node.AddNewNode("Level 1.1") Node.AddNewNode("Level 1.2") Node.AddNewNode("Level 1.3") Node.Value = Node.GetNode(0) Node.AddNewNode("Level 2.1") Node.AddNewNode("Level 2.2") Node.Value = Node.Parent Node.Value = Node.GetNode(1) Node.AddNewNode("Level 2.3") Node.AddNewNode("Level 2.4") Tree.ExpandAll Msgbox(GetControls("Tree")) ' Initialize TempNode TempNode.New1 ' Prepare Result of recursive call Result = "" ' Initialize node for recursive call Node.Value = Tree.GetNode(0) ' Recursice Call RecursiveDescent("Node", 1) ' Use result Msgbox(Result,"Result") End Sub
Sub RecursiveDescent(NodeName, Level) ' Do something for each node: Result = Result & Control(NodeName).Text & "" SubNode = "Node"&Level AddObject(SubNode, "Node") Control(SubNode).New1 nodeCount = Control(NodeName).Count - 1 For i = 0To nodeCount Control(SubNode).Value = Control(nodeName).GetNode(i).Value RecursiveDescent (SubNode, Level+1) Next Control(SubNode).Dispose End Sub
Cannot (always) use Objects as parameters
Linear Mode
