Detecting rectangle on android

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I am trying to detect rectangle in a picture taken by android.

After of several days struggling I am still unable to do this. It surprises me that I am unable to find this kind of example. I found several solutions with cpp but not something that can easily be ported on android.

I am new to opencv and in computer vision in general.

Can someone please give me some simple sample project that detects rectangle in android ? That will be very helpful to me at this moment.

Thanks in advance