[SOLVED] child of parent node

[petevick]

I have the following code, it displays a message based on the contents of a selected folder in a TShellTreeView. On the first selction I get no error but I get an "External: SIGSEGV" error on the second selection at line 9, as pChild is Nil at line 8. I know for sure that the selected folder does have a child as line 7 qualifies it, also cParent is valid just before the error.
So what have I done that causes the error ?

Code: Pascal  [Select][+][-]

1. procedure TBrowser.SelectFolderClick(Sender: TObject);
2. var
3.   Reply: Integer = mrYes;
4.   pChild, cParent: TTreeNode;
5. begin
6.  cParent:= myTreeView.Selected;
7.    if cParent.HasChildren = True then begin
8.      pChild:= cParent.GetFirstChild;
9.      if (pChild.Text = 'icons') and (pChild.GetNextChild(pChild)=Nil) then
10.        Reply:= MessageDlg('Existing Folder',
11.            'You have selected an icons folder'
12.            , mtConfirmation, [mbClose], 0)
13.      else
14.        Reply:= MessageDlg('Unsuitable Folder',
15.            'The selected folder is not empty.'
16.            , mtWarning, [mbClose], 0);
17.    end;
18.   if Reply = mrYes then ModalResult:= mrYes;
19. end;
20.  

[bytebites]

Maybe cParent instead if pChild?

Code: Pascal  [Select][+][-]

1.  if (pChild.Text = 'icons') and (cParent.GetNextChild(pChild)=Nil) then

[petevick]

Maybe cParent instead if pChild?

Code: Pascal  [Select][+][-]

1.  if (pChild.Text = 'icons') and (cParent.GetNextChild(pChild)=Nil) then

Possibly, but it would still fail at line 9 as pChild is Nil on the second selection.

[petevick]

Even using the following I still get the same error on the second selection....

Code: Pascal  [Select][+][-]

1. procedure TBrowser.SelectFolderClick(Sender: TObject);
2. var
3.   Reply: Integer = mrYes;
4.   cCount: Integer;
5.   pChild, cParent: TTreeNode;
6. begin
7.  cParent:=myTreeView.Selected;
8.    if cParent.HasChildren then begin
9.      cCount:= cParent.SubTreeCount;
10.      pChild:= cParent.GetFirstChild;
11.      if (pChild.Text = 'icons') and (cCount = 1) then
12.        Reply:= MessageDlg('Existing Folder',
13.            'You have selected an icons folder'
14.            , mtConfirmation, [mbClose], 0);
15.      if (pChild.Text <> 'icons') and (cCount > 1) then
16.        Reply:= MessageDlg('Unsuitable Folder',
17.            'The selected folder is not empty.'
18.            , mtWarning, [mbClose], 0);
19.    end;
20.    if Reply = mrYes then ModalResult:= mrYes;
21. end;

[ASerge]

In some cases, HasChildren doesn't mean that it has items, but that's just that it's a folder. So you can do it like this:

Code: Pascal  [Select][+][-]

1. procedure TBrowser.SelectFolderClick(Sender: TObject);
2. const
3.   CCaption: array[Boolean] of string = ('Unsuitable Folder', 'Existing Folder');
4.   CMsg: array[Boolean] of string = ('The selected folder is not empty.', 'You have selected an icons folder');
5.   CDlgType: array[Boolean] of TMsgDlgType = (mtWarning, mtConfirmation);
6. var
7.   Suitable: Boolean;
8.   Child, Selected: TTreeNode;
9. begin
10.   Selected := myTreeView.Selected;
11.   if Selected = nil then
12.     Exit;
13.   Child := Selected.GetFirstChild;
14.   if Child <> nil then
15.   begin
16.     Suitable := SameFileName(Child.Text, 'icons') and (Child.GetFirstChild = nil);
17.     if MessageDlg(CCaption[Suitable], CMsg[Suitable], CDlgType[Suitable], [mbClose], 0) = mrYes then
18.       ModalResult := mrYes;
19.   end;
20. end;

[wp]

It could be that child node has not yet been created even although the parent's HasChildren signals the presence of children. This is just a flag to indicate that the expand icon must be drawn, but the populating process might have stopped at the parent level. Partial creation of the nodes has been implemented to save time and memory because directory trees can be huge.

It is my impression that thinking in terms of the file system is a better strategy for special navigating the shelltree than thinking in terms of nodes.

[petevick]

It could be that child node has not yet been created even although the parent's HasChildren signals the presence of children. This is just a flag to indicate that the expand icon must be drawn, but the populating process might have stopped at the parent level. Partial reading of the nodes has been implemented to save time and memory because directory trees can be huge.

It is my impression that thinking in terms of the file system is a better strategy for special navigating the shelltree than thinking in terms of nodes.

That makes sense wp. I think I'll have to be more generic with the mesages.

[petevick]

Using myTreeView.Path and DirectoryExists() I can get the same message results.