Invalid Pointer Operation
delphi, openfiledialog
Solution
"Invalid pointer operation" means you freed memory that didn't belong to you. One of these three things is the cause:
- Your program freed something that had already been freed once before.
- Your program freed something that was never allocated in the first place.
- Your program freed something that had been allocated with a different memory manager.
In your code, you're freeing the `TOpenDialog`'s `Files` property. You didn't allocate that string list, and the documentation doesn't tell you to free it, so it's reasonable to expect that the list actually belongs to the dialog component, and that the component will free it when it wants. Checking the source code in Dialogs.pas confirms that. Since you have also freed that object, you have a double-free error, which meets the first criterion I listed above. Remove that line.
As Uwe pointed out, you're also processing a list of file names but only checking the existence of one. That's a logic error in your program, but it would not cause the exception you're seeing.
Problem
I have a form that contains a `TOpenDialog` component (`OpenDialog1`) and a button. `OpenDialog1` has the `ofAllowMultiSelect` (of `Options`) property set to true. Upon clicking the button the method `AddFilesToListView` is executed: ``` procedure TForm4.AddFilesToListView(); var ListItem : TListItem; I: Integer; F : File; LengthOfAudio : TDateTime; previousCursor : TCursor; begin previousCursor := Self.Cursor; Self.Cursor := crHourGlass; if OpenDialog1.Execute then begin for I := 0 to OpenDialog1.Files.Count - 1 do begin if FileExists(OpenDialog1.FileName) then begin ListItem:=ListView1.Items.Add; ListItem.Caption := 'Test'; ListItem.SubItems.Add(ExtractFileName(OpenDialog1.Files[I])); ListItem.SubItems.Add(ExtractFilePath(OpenDialog1.Files[I])); end else raise Exception.Create('File does not exist.'); end; end; Self.Cursor := previousCursor; OpenDialog1.Files.Free; end; ``` When running the application, selecting the first file, I have no problem but when wanting to select the second one, I get an error saying "Project project3 raised an exception class EInvalidPointer with message 'Invalid Pointer Operation'." What's the cause of this, how do I correct this?