How to clear the tokens saved in history

Hi Guys, In my application i am storing the history tokens when moving backward or forward .Activities and places have been used. There is a kind of form that need to be filled and when user clicks on submit the token is created and we navigate to a new place. The problem is when i am clicking

how to create columns with common header in data grid.

https://lh5.googleusercontent.com/-SA2dPCsyiG8/UNwthugGWXI/A2c/l1qY23f-GYo/s1600/TABLE.JPG === see the attached files for this question. I AM HAVING A,B,C AS MAIN HEADERS AND D,E,F,G AS THE SUB HEADERS UNDER C. how can i create these columns in data grid

HOW TO APPLY SORTING FOR THESE SUB HEADERS

https://lh6.googleusercontent.com/-lgTroTRdUYQ/UMVtHCus--I/A2E/NPOEuRciI-s/s1600/TABLE.JPG SO THIS IS A TABLE FOR EX.. I AM HAVING A,B,C AS MAIN HEADERS AND D,E,F,G AS THE SUB HEADERS UNDER C. sO HOW TO APPLY SORTING FOR THESE SUB HEADERS ALSO. -- You received this message because

how to apply sorting to columns with individual header and these columns are merged under a common header also

https://lh5.googleusercontent.com/-3l8DaFsEPeo/UMHFiiTl8dI/A10/PfrRT4ppQTI/s1600/TABLE.JPG SO THIS IS A TABLE FOR EX.. I AM HAVING A,B,C AS MAIN HEADERS AND D,E,F,G AS THE SUB HEADERS UNDER C. sO HOW TO APPLY SORTING FOR THESE SUB HEADERS ALSO. -- You received this message because