[vtkusers] Accessing keys in vtkInformation without having key pointers at first

[Sunrise]

I would like to find /search for keys appended in vtkInformation object and
then access their values. But, it seems that if we do not have key pointers,
we can not inquiry the vtkInformaton that which key-pairs it contains!Assume
I have vtkInformation *inputInfo object in Filter2, that coming from
previous filter (Filter1) in a pipeline. Filter1 added some key/value pairs
of type vtkInformationDoubleVectorkey into outputInfo object. Now, in the
new filter (Filter2) I want to access DoubleVector key.In Filter1 header, a
key is defined with a static function:static vtkInformationDoubleVectorKey *
MyKey();key-value pair is appended to outputInfo
with:outputInfo->Set(Filter1::MyKey(),someValues,someLength);So in Filter2
by calling Filter1::MyKey(), I can access the key values via:values =
inputInfo->Get(Filter1::MyKey());But, the problem is that Filter1 could be
one of more general filters that create their own key. Filter2 is not
restricted to be connected just to Filter1, downstream of Filter2 can be
FilterX. So I do not know which FilterX generated key for DoubleVector type
in inputInfo. "All the Filter2 should know is that in inputInfo there is a
key-value pair with DoubleVector type".Also I don't want to create a
superclass for my filters and generate keys at there (something that
vtkStreamingDemandDrivenPipeline does for its keys).I looked at this thread 
http://vtk.1045678.n5.nabble.com/vtkInformation-access-with-equivalent-keys-td5545920.html
<http://vtk.1045678.n5.nabble.com/vtkInformation-access-with-equivalent-keys-td5545920.html> 
to figure out how can I access keys with other similar key-types. The answer
suggests to use CopyEntries method. If you look at source code for
vtkInformation::CopyEntries(...), you will see that keys in info should be
know again in order to use CopyEntries.Any idea would be appreciated.



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