4 years later I was having a similar problem with this situation. Some stuff has been deprecated and stuff no longer works. So for those of you who want to know how to do it now, in 2018... check this answer-
First you have to get the LeaderBoardClient with
mLeaderboardsClient = Games.getLeaderboardsClient(MainActivity.this, googleSignInAccount);
Next you can the score
mLeaderboardsClient.loadCurrentPlayerLeaderboardScore(getString(R.string.leaderboard_id), LeaderboardVariant.TIME_SPAN_ALL_TIME, LeaderboardVariant.COLLECTION_PUBLIC)
.addOnSuccessListener(this, new OnSuccessListener<AnnotatedData<LeaderboardScore>>() {
@Override
public void onSuccess(AnnotatedData<LeaderboardScore> leaderboardScoreAnnotatedData) {
long score = 0L;
if (leaderboardScoreAnnotatedData != null) {
if (leaderboardScoreAnnotatedData.get() != null) {
score = leaderboardScoreAnnotatedData.get().getRawScore();
Toast.makeText(MainActivity.this, Long.toString(score), Toast.LENGTH_SHORT).show();
Log.d(TAG, "LeaderBoard: " + Long.toString(score));
} else {
Toast.makeText(MainActivity.this, "no data at .get()", Toast.LENGTH_SHORT).show();
Log.d(TAG, "LeaderBoard: .get() is null");
}
} else {
Toast.makeText(MainActivity.this, "no data...", Toast.LENGTH_SHORT).show();
Log.d(TAG, "LeaderBoard: " + Long.toString(score));
}
}
})
.addOnFailureListener(new OnFailureListener() {
@Override
public void onFailure(@NonNull Exception e) {
Toast.makeText(MainActivity.this, "Failure", Toast.LENGTH_SHORT).show();
Log.d(TAG, "LeaderBoard: FAILURE");
}
});
The 3 parameters to .loadCurrentPlayerLeaderboardScore are as follows
ID of the leaderboard to load the score from.
Time span to retrieve data for. Valid values are TIME_SPAN_DAILY, TIME_SPAN_WEEKLY, or TIME_SPAN_ALL_TIME.
The leaderboard collection to retrieve scores for. Valid values are either COLLECTION_PUBLIC or COLLECTION_SOCIAL.