code: public void registerView(@Nullable RegisterViewStatusListener callback) {
          if (Branch.getInstance() != null) {
              Branch.getInstance().registerView(this, callback);
          } else {
              if (callback != null) {
                  callback.onRegisterViewFinished(false, new BranchError("Register view error", BranchError.ERR_BRANCH_NOT_INSTANTIATED));
              }
          }
      }
docs: Mark the content referred by this object as viewed. This increment the view count of the contents referred by this object.
  
  @param callback An instance of {@link RegisterViewStatusListener} to listen to results of the operation