liuxg@liuxg:~$ sudo apt-get purge qtcreator-plugin-ubuntu 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages will be REMOVED:
  qtcreator-plugin-ubuntu*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
(Reading database ... 308651 files and directories currently installed.)
Removing qtcreator-plugin-ubuntu (3.1.1+15.10.20150720-0ubuntu1~0vivid1) ...
Purging configuration files for qtcreator-plugin-ubuntu (3.1.1+15.10.20150720-0ubuntu1~0vivid1) ...
liuxg@liuxg:~$  sudo apt-get install ubuntu-sdk
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 ubuntu-sdk : Depends: ubuntu-sdk-libs-dev but it is not going to be installed
              Depends: qtcreator-plugin-ubuntu but it is not going to be installed
E: Unable to correct problems, you have held broken packages.