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Tags: 2017 source edit, Replaced |
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| | <noinclude>{{documentation/versioncheck}}</noinclude> | | <noinclude>{{documentation/versioncheck}}</noinclude> |
| − | From http://massmail.spl.harvard.edu/public-archives/slicer-devel/2011/007513.html
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| | | | |
| − | Like VTK, Slicer contains some "factory" methods:
| + | {{documentation/banner |
| − | - vtkMRMLScene::CreateNodeByClass() | + | | text = [https://slicer.readthedocs.io/en/latest/developer_guide/advanced_topics.html#memory-management This page has been moved to read-the-docs.] |
| − | - vtkMRMLScene::GetNodesByClass()
| + | | background-color = 8FBC8F }} |
| − | - ...
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| − | Like in C++, it means that the functions return an object with a reference
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| − | count of 1 that nobody "owns" and the caller must take care of releasing
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| − | the object to avoid memory leak.
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| − | | |
| − | While there is workaround for some methods (
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| − | slicer.mrmlScene.CreateNodeByClass('vtkMRMLModelNode') should be replaced | |
| − | by slicer.vtkMRMLModelNode() ) there is currently no automatic/clean
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| − | mechanism to release the object created by such methods.
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| − | | |
| − | The only "hack" that exists for now is to decrease the reference count
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| − | manually in your code:
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| − | | |
| − | nodes = slicer.mrmlScene.GetNodesByClass('vtkMRMLLinearTransformNode')
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| − | nodes.UnRegister(slicer.mrmlScene) # ----> (reference count was 2, keep 1 for the python reference)
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| − | ...
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| − | | |
| − | In C++, the following would apply:
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| − | vtkCollection* nodes =
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| − | mrmlScene->GetNodesByClass("vtkMRMLLinearTransformNode");
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| − | ...
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| − | nodes->Delete();
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| − | | |
| − | or using vtkSmartPointer:
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| − | vtkSmartPointer<vtkCollection> nodes;
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| − | nodes.TakeReference(mrmlScene->GetNodesByClass("vtkMRMLLinearTransformNode"));
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| − | ...
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| − | | |
| − | Amendment from JC http://viewvc.slicer.org/viewvc.cgi/Slicer4?view=revision&revision=19772
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| − | | |
| − | The reference count shouldn't be decreased using the naive approach where
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| − | it is set to one. Indeed, internally, the reference count could be any
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| − | number greater than one. It doesn't have to be 2.
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| − | | |
| − | Considering this last remark, using the following approach is *REQUIRED*,
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| − | otherwise it will lead to a CRASH of the application.
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| − | | |
| − | n = slicer.mrmlScene.CreateNodeByClass('vtkMRMLViewNode')
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| − | slicer.mrmlScene.addNode(n)
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| − | n.UnRegister(slicer.mrmlScene)
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| − | | |
| − | Even better, this specific example can be simplified using the following
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| − | syntax, this is the *RECOMMENDED* approach, it will prevent bug, memory
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| − | leaks and crashes:
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| − | | |
| − | n = slicer.mrmlScene.addNode(slicer.vtkMRMLViewNode())
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| − | | |
| − | And if the name of the node is generated at runtime, this could be done:
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| − | | |
| − | n = eval('slicer.mrmlScene.AddNode(slicer.%s())' % 'vtkMRMLViewNode')
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