Is it a good idea for applications (application developers) to replace the check mark icon in the contextual action bar when in selection mode. Is this a good design pattern? Does it make more sense to replace that check mark with an "x"? Does it break consistency? Will it confuse users? The android selection pattern refers to the checkmark as a done action. Here's a link for some more details:
I quote from the Action Bar page:
A contextual action bar (CAB) is a temporary action bar that overlays the app's action bar for the duration of a particular sub-task. CABs are most typically used for tasks that involve acting on selected data or text.
The check sign gives you visual feedback that you have actually selected something. It is a sign that most users would have associated during their education with getting something right.
An "x" would mean that you would want to close a window or other visual element, which is not what happens here. Android users are used to pressing the Back button to return to the previous state of the application (before the selection happened).
Overall, an "x" would break consistency and would confuse users in two ways: it would give feedback that the app failed to be in a temporary selection state, and would override expectations of the "back" button's functionality.
I had a difficult time with this checkmark in the android selection UI. To complicate the issue further on devices such as the Kindle Fire the checkmark is further augmented with a 'Done' label that communicates more of a complete this step sort of behavior to the user.
Ultimately I think this comes down to your app's audience, if you expect your customers to be Android interface convention saavy (or uses Google's own Android apps) then I think sticking with default conventions here is in your favor. However if your customers are less tech savvy or don't use a lot of other apps there may be reason to consider being more explicit in this interaction than this default selection pattern.
I sided with accepting the default behavior, with the reservation to reconsider this UX/UI if I witnessed confusion from our customers during usability research.