How to add android library project in another android project in eclipse

How to add android library project in another android project in eclipse

I am trying to add a library project in another project but I am unable to
add it.
I made e.g. Project A as a library project by going in to its properties
and checking isLibrary checkbox. Then I tried to add this in Project B ,
by going into its properties , and by clicking Add button and selecting
Project A as a library.
Then I clicked on ok , but when I try to use any class or reference of
Project A , I get an error that it is not defined. I checked Project B's
properties again , and there is no reference there of Project A, which I
established earlier.
The reference is automatically disappearing. I need help in this.
Edit : Both Projects are in same workspace.