这个会话列表怎么做的，请教下思路

- (void)tableViewDidTriggerHeaderRefresh
{
    NSArray *conversations = [[EaseMob sharedInstance].chatManager conversations];
    NSArray* sorted = [conversations sortedArrayUsingComparator:
                       ^(EMConversation *obj1, EMConversation* obj2){
                           EMMessage *message1 = [obj1 latestMessage];
                           EMMessage *message2 = [obj2 latestMessage];
                           if(message1.timestamp > message2.timestamp) {
                               return(NSComparisonResult)NSOrderedAscending;
                           }else {
                               return(NSComparisonResult)NSOrderedDescending;
                           }
                       }];
    
    
    
    [self.dataArray removeAllObjects];
    for (EMConversation *converstion in sorted) {
        EaseConversationModel *model = nil;
        if (_dataSource && [_dataSource respondsToSelector:@selector(conversationListViewController:modelForConversation:)]) {
            model = [_dataSource conversationListViewController:self
                                           modelForConversation:converstion];
        }
        else{
            model = [[EaseConversationModel alloc] initWithConversation:converstion];
        }
        
        if (model) {
            [self.dataArray addObject:model];
        }
    }

    [self tableViewDidFinishTriggerHeader:YES reload:YES];
}
这是easeUI中获取会话列表并按最后一条消息的时间戳排序的代码。