[vtk-developers] vtkFileOutputWindow syntax

[David Cole]

On Tue, Jun 12, 2012 at 7:20 AM, David Doria <daviddoria at gmail.com> wrote:

> The documentation for this class says:
> http://www.vtk.org/doc/nightly/html/classvtkFileOutputWindow.html#details
>
> "To use this class, instantiate it and then call SetInstance(this)."
>
> It seems like you have to do this:
>
>   vtkSmartPointer<vtkFileOutputWindow> fileOutputWindow =
>       vtkSmartPointer<vtkFileOutputWindow>::New();
>   fileOutputWindow->SetFileName( "output2.txt" );
>   fileOutputWindow->SetInstance( fileOutputWindow );
>
> If you are supposed to call SetInstance(this), why not just set that
> internally and not require a SetInstance call at all?
>
> David
>
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SetInstance is a *static* method. It keeps track of a single instance of
(possibly many) vtkOutputWindow objects.

You do not necessarily want to call SetInstance every time you create a
vtkOutputWindow, therefore you have to call it manually/intentionally when
you actually do want to record a specific instance as "*the* output
window"...

This is a very common occurrence when following the Singleton pattern.


HTH,
David C.
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