[vtkusers] Can vtkDataObject be downcasted to vtkUnstructuredGrid?

[Mathieu Westphal]

Hello

For the cast to work, the object need to be of the right type. If the
output is a vtkPolyData, it cannot be a vtkUnstructuredGrid.
Take a look at the polymorphism here.

https://www.vtk.org/doc/nightly/html/classvtkDataSet.html

Best,

Mathieu Westphal

On Thu, Nov 16, 2017 at 5:30 AM, landings <landinghere at 163.com> wrote:

> Hi,
>
> I am writing a reader that outputs an unstructured solid mesh.
>
> I am referring to vtkSTLReader, in its RequestData() method I can see the
> following code:
>
>     vtkInformation *outInfo = outputVector->GetInformationObject(0);
>     vtkPolyData *output =
> vtkPolyData::SafeDownCast(outInfo->Get(vtkDataObject::DATA_OBJECT()));
>
> But when I do similar things:
>
>     vtkInformation* outInfo = outputVector->GetInformationObject(0);
>     vtkUnstructuredGrid *output =
> vtkUnstructuredGrid::SafeDownCast(outInfo->Get(
> vtkDataObject::DATA_OBJECT()));
>
> I get a nullptr for output. I am sure
> outInfo->Get(vtkDataObject::DATA_OBJECT()) exists before downcasting.
>
>
>
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