uitableview滚动到最后一行

- (void)scrollTableToFoot:(BOOL)animated {
    NSInteger s = [self.chatTable numberOfSections];
	if (s<1) return;
	NSInteger r = [self.chatTable numberOfRowsInSection:s-1];
	if (r<1) return;
	
	NSIndexPath *ip = [NSIndexPath indexPathForRow:r-1 inSection:s-1];
	
	[self.chatTable scrollToRowAtIndexPath:ip atScrollPosition:UITableViewScrollPositionBottom animated:animated];
}