Ios 筛选包含消息列表的NSMutableArray

我正在尝试对包含聊天消息列表的NSMutableArray进行筛选和排序。我正在尝试获取两个用户之间对话的最后一条消息。例如，如果user1与两个不同的用户有两个不同的对话，我希望获得每个对话的最后一条消息。我使用Parse.com作为后端，这是我保存和检索邮件的方式

保存消息

PFUser *user = [[PFUser currentUser] objectForKey:@"displayName"];
PFObject *newMessage = [PFObject objectWithClassName:@"Messages"];
[newMessage setObject:messageStr forKey:@"body"];
[newMessage setObject:self.mySelectedUser forKey:@"toUser"];
[newMessage setObject:user forKey:@"fromUser"];
[newMessage saveInBackground];
myMessageField.text = @"";
[self getTheNewMessages];
[self.myTView reloadData];

-(void)GetmyNewMessages

{
PFQuery *query1 = [PFQuery queryWithClassName:@"Messages"];
[query1 whereKey:@"toUser"  equalTo:[[PFUser currentUser] objectForKey:@"displayName"]];
 [query1 whereKeyExists:@"date"];

PFQuery *query2 = [PFQuery queryWithClassName:@"Messages"];
[query2 whereKey:@"fromUser" equalTo:[[PFUser currentUser] objectForKey:@"displayName"]];
[query2 whereKeyExists:@"date"];

 PFQuery *query = [PFQuery orQueryWithSubqueries:[NSArray arrayWithObjects:query1, query2, nil]];

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (!error) {


             NSLog(@"Successfully retrieved %d chats.", objects.count);
            [premessagesList removeAllObjects];
            [premessagesList addObject:objects];
     } else {
            //Log details of the failure
            NSLog(@"Error: %@ %@", error, [error userInfo]);


        }


    }];

检索消息

PFUser *user = [[PFUser currentUser] objectForKey:@"displayName"];
PFObject *newMessage = [PFObject objectWithClassName:@"Messages"];
[newMessage setObject:messageStr forKey:@"body"];
[newMessage setObject:self.mySelectedUser forKey:@"toUser"];
[newMessage setObject:user forKey:@"fromUser"];
[newMessage saveInBackground];
myMessageField.text = @"";
[self getTheNewMessages];
[self.myTView reloadData];

-(void)GetmyNewMessages

{
PFQuery *query1 = [PFQuery queryWithClassName:@"Messages"];
[query1 whereKey:@"toUser"  equalTo:[[PFUser currentUser] objectForKey:@"displayName"]];
 [query1 whereKeyExists:@"date"];

PFQuery *query2 = [PFQuery queryWithClassName:@"Messages"];
[query2 whereKey:@"fromUser" equalTo:[[PFUser currentUser] objectForKey:@"displayName"]];
[query2 whereKeyExists:@"date"];

 PFQuery *query = [PFQuery orQueryWithSubqueries:[NSArray arrayWithObjects:query1, query2, nil]];

[query findObjectsInBackgroundWithBlock:^(NSArray *objects, NSError *error) {
        if (!error) {


             NSLog(@"Successfully retrieved %d chats.", objects.count);
            [premessagesList removeAllObjects];
            [premessagesList addObject:objects];
     } else {
            //Log details of the failure
            NSLog(@"Error: %@ %@", error, [error userInfo]);


        }


    }];

}

NSMutableArray的NSLog（premessageList）

（“{\n
body=hi；\n fromUser=cnn；\n toUser=FNC；\n
日期=\“2012-09-19 02:40:29+0000\”；\n}“，
“{\n
body=hello；\n fromUser=FNC；\n toUser=cnn；\n
日期=\“2012-09-20 05:06:05+0000\”；\n}“，
“{\n
body=whatsgood；\n fromUser=sleepy；\n toUser=cnn；\n
日期=\“2012-09-20 05:06:05+0000\”；\n}“，
“{\n
body=lol；\n fromUser=cnn；\n toUser=sleepy；\n
日期=\“2012-09-20 05:13:16+0000\”；\n}“，

---

我试图使用NSSortDescriptor和NSPredicate，但我得到了一个空的tableview。

在这种类型的问题中，我会使用一些变量和快速迭代来遍历信息，并获得您需要的：

id lastChat = ni;
... temps 

for(OneChat in allChats) {
  do tests and set variables
}

Now I know the last chat.

---

PS：我决定不发布这篇文章，但当我看到很久没有人回复时，我觉得这总比什么都没有好。这就是我解决这一问题的方法。

在这种类型的问题中，我会使用一些变量和快速迭代来费力地浏览信息，并得到你需要的：

id lastChat = ni;
... temps 

for(OneChat in allChats) {
  do tests and set variables
}

Now I know the last chat.

---

PS：我决定不发布这篇文章，但当我看到很长一段时间后没有人回复时，我觉得这总比没有好。这就是我解决这个问题的方法。

你可以限制结果并像这样对

PFQuery

本身进行排序：

[query1 orderByDescending:@"createdAt"];
query1.limit = 1;
[query2 orderByDescending:@"createdAt"];
query2.limit = 1;

---

您可以限制结果并通过

PFQuery

本身进行排序，如下所示：

[query1 orderByDescending:@"createdAt"];
query1.limit = 1;
[query2 orderByDescending:@"createdAt"];
query2.limit = 1;