How to build this library for a jar?

[qq280948982]

I saw the ReadMe wrote:
"If you rather want a jar file instead of a including the project as an android library, run ant jar in the android-viewflow/viewflow folder, to build a jar file."
I had try the step, but it build a empty jar for me, can anybody help me?

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update: I use Eclipse to build a jar, and import in other project, but it throws an InflateException, Caused by: java.lang.NoClassDefFoundError: org.taptwo.android.widget.viewflow.R$styleable, but I had already copy the attrs.xml from source code to my project, is threre some thing I have mistake?