ios - NSMutableArray 中的 __NSCFString 在分配它的函数之外变为 nil

Question

我的应用程序中有一个代表用户的类 OtherUser .这个类包含几个 NSString *特性。当我用静态 @"string" 分配这些属性时字符串，属性保存为__NSCFConstantString *值(value)观。当我为它们分配从 JSON 转换的字符串时，它们被保存为 __NSCFString *值(value)观。我正在保存 OtherUser 的可变数组的可变数组对象。当我在分配了值的函数之外访问数组时，只有 __NSCFConstantString *值仍然存在，而 __NSCFString *值全部变为 nil。有没有办法将我的 NSCFString 对象转换为 NSCFConstantString 对象，或者有什么方法可以解决这个限制？

This是在我的 ConnectionDidFinishLoading 方法中分配了所有值后数组的样子。用户测试 Testman 是使用下载的 JSON 数据创建的，而用户 Rose Lalonde 是使用 @"string" 在本地创建的值(value)观。

This当我在我的 CellForRowAtIndexPath 中再次拉起它时，该数组的样子是什么？方法。 Test Testman 丢失了除 ID 之外的所有数据，而 Rose Lalonde 保留了她的所有数据。 (我为链接图像而不是嵌入而道歉 - 我的代表还不足以嵌入图像)。

这是我的 connectionDidFinishLoading 方法，首先调用它并创建数组:

//Called when the connection finishes loading all data
- (void)connectionDidFinishLoading:(NSURLConnection *)connection {
    NSLog(@"Connection finished!");

    //Converts downloaded JSON data to an array
    NSError *error = [[NSError alloc] init];
    NSArray *arr = [NSJSONSerialization JSONObjectWithData:_responseData
                                                   options:kNilOptions
                                                     error:&error];

    //Checks if the array was properly instantiated
    if (!arr) {
        NSLog(@"Error parsing JSON: %@", error);
    } else {
        //Initializes the arrays if they are not already initialized
        if (!_bestFriends) _bestFriends = [[NSMutableArray alloc] init];
        if (!_onlineFriends) _onlineFriends = [[NSMutableArray alloc] init];
        if (!_offlineFriends) _offlineFriends = [[NSMutableArray alloc] init];

        //Loops through each result dictionary and creates a friend object with its contents
        for(NSDictionary *item in arr) {
            OtherUser *friend = [[OtherUser alloc] init];
            friend.firstname = [NSString stringWithString:(NSString *)[item objectForKey:@"firstname"]];
            friend.lastname = (NSString *)[item objectForKey:@"lastname"];
            friend.username = (NSString *)[item objectForKey:@"username"];
            friend.userID = [NSNumber numberWithInt:[(NSString *)[item objectForKey:@"userID"] intValue]];
            friend.isOnline = [(NSString *)[item objectForKey:@"isOnline"] boolValue];
            friend.isInSession = [(NSString *)[item objectForKey:@"isInSession"] boolValue];

            //Sorts the friend into online or offline
            if (friend.isOnline) {
                [_onlineFriends addObject:friend];
            } else {
                [_offlineFriends addObject:friend];
            }
        }

        //user object created with local data to test best friends array
        OtherUser *tempUser = [[OtherUser alloc] initWithFirstname:@"John"
                                                          Lastname:@"Egbert"
                                                          Username:@"ectobiologist"
                                                            UserID:[NSNumber numberWithInt:10]
                                                       OnlineState:YES
                                                      SessionState:NO];
        [_bestFriends addObject:tempUser];

        //User created with local data to compare to downloaded JSON users
        OtherUser *tempUser2 = [[OtherUser alloc] initWithFirstname:@"Rose"
                                                           Lastname:@"Lalonde"
                                                           Username:@"tentacletherapist"
                                                             UserID:[NSNumber numberWithInt:15]
                                                        OnlineState:YES
                                                       SessionState:NO];
        [_onlineFriends addObject:tempUser2];
    }

    //Adds the arrays to the array array
    self.arrays = [NSMutableArray arrayWithObjects:_bestFriends, _onlineFriends, _offlineFriends, nil];

    //Resets the table data
    [self.tableView reloadData];
    NSLog(@"reloading data...");
}

我的 CellForRowAtIndexPath 方法，接下来将被调用并且是数组数据被删除的地方，如下所示:

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath {
    NSLog(@"Creating Cell...");
    UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];

    //Creates a user object from the proper index of the proper array (e.g. _onlineFriends[1])
    OtherUser *friend = [[_arrays objectAtIndex:indexPath.section] objectAtIndex:indexPath.row];

    // Configure Cell
    UILabel *label = (UILabel *)[cell.contentView viewWithTag:10];
    [label setText:[friend fullname]];

    NSLog(@"Cell created!");
    return cell;
}

还有我的 FriendsTableViewController.h 文件，以防万一:

@interface FriendsTableViewController : UITableViewController <NSURLConnectionDelegate> {
    NSMutableData *_responseData;
    NSMutableArray *_onlineFriends;
    NSMutableArray *_bestFriends;
    NSMutableArray *_offlineFriends;
}

@property NSMutableArray *arrays;

编辑:其他用户文件:

//OtherUser.h
#import <Foundation/Foundation.h>

@interface OtherUser : NSObject

@property (weak, nonatomic) NSNumber *userID;
@property (weak, nonatomic) NSString *firstname;
@property (weak, nonatomic) NSString *lastname;
@property (weak, nonatomic) NSString *username;
@property (nonatomic, assign) BOOL isOnline;
@property (nonatomic, assign) BOOL isInSession;
@property (weak, nonatomic) NSNumber *sessionID;

- (id)initWithFirstname:(NSString *)firstName Lastname:(NSString *)lastName
               Username:(NSString *)userName UserID:(NSNumber *)uID
            OnlineState:(BOOL)online SessionState:(BOOL)inSession;
- (id) init;

- (NSString *) fullname;

//OtherUser.m

//Initializes an empty User object
- (id)init {
    self = [super init];
    if (self) {
        self.userID = 0;
        self.username = @"";
        self.firstname = @"";
        self.lastname = @"";
        self.isOnline = NO;
        self.isInSession = NO;

        return self;
    }
    return nil;
}

- (id)initWithFirstname:(NSString *)firstName Lastname:(NSString *)lastName
               Username:(NSString *)userName UserID:(NSNumber *)uID
            OnlineState:(BOOL)online SessionState:(BOOL)inSession {
    self = [super init];

    if (self) {
        self.userID = uID;
        self.username = userName;
        self.firstname = firstName;
        self.lastname = lastName;
        self.isOnline = online;
        self.isInSession = inSession;

        NSLog(@"Friend %@ %@ created.", self.firstname, self.lastname);

        return self;
    }
    return nil;
}

- (NSString *)fullname {
    return [NSString stringWithFormat:@"%@ %@", self.firstname, self.lastname];
}

Answer 1

您已将“名字”、“姓氏”和其他属性声明为弱:

@property (weak, nonatomic) NSString *firstname;

这意味着它们不保留引用的对象，并将设置为 nil如果引用的对象被释放。当 JSON 数组 arr去
超出范围。 NSString文字是静态分配的，永远不会被释放，
这就是为什么 Rose Lalonde 不会失去这里的属性。

您应该将 Objective-C 属性声明为 strong，或者 - 在字符串的情况下 - 作为副本:

@property (copy, nonatomic) NSString *firstname;
// ...
@property (strong, nonatomic) NSNumber *sessionID;

顺便说一句，所有类型转换和 stringWithString呼入

friend.firstname = [NSString stringWithString:(NSString *)[item objectForKey:@"firstname"]];
friend.lastname = (NSString *)[item objectForKey:@"lastname"];
// ...

没有必要，你可以简单地写成

friend.firstname = [item objectForKey:@"firstname"];
friend.lastname = [item objectForKey:@"lastname"];

或者，使用(较新的)下标符号:

friend.firstname = item[@"firstname"];
friend.lastname = item[@"lastname"];