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The results are represented in fig.1 below.

skeletonNode = [SkeletonAnimation skeletonWithFile:jsonFile atlasFile:atlasFile scale:scale];

How to judge the validity of skeletonNode ?

thanks!

Take a look at the code, if SkeletonBinary/SkeletonJson readSkeletonDataFile fails to read the file, it does a CCASSERT with the error message:
https://github.com/EsotericSoftware/spine-runtimes/blob/5a1d53bb16f04b19840383898db9d22e59a3e8a0/spine-cocos2dx/src/spine/SkeletonRenderer.cpp#L240

You could load the SkeletonData yourself, just as that code does, but take some other action on failure. If you load the data successfully you can, for example, pass it to the SkeletonAnimation createWithData methods.