Question

我使用准备segue将字符串发送到下一个控制器。它被设置为一个字符串直到被发送（根据NSLog），但是一旦我将它记录在下一个控制器上它就是一个NSObject而不是一个字符串，因此该值变为null。

这是第一个视图控制器，bodyText字段是我试图发送到下一个视图控制器的：

#import "GFAddPostTextViewController.h"
#import "GFSelectGroupViewController.h"

@interface GFAddPostTextViewController ()
@property (weak, nonatomic) IBOutlet UITextField *bodyTextField;
@end

@implementation GFAddPostTextViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
}

-(void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {

    if([segue.identifier isEqualToString:@"selectGroup"]) {

        GFSelectGroupViewController *destViewController = segue.destinationViewController;

        destViewController.bodyText = self.bodyTextField.text;

        NSLog(@"%@", destViewController.bodyText);

    }

}


@end

以下是接收视图控制器的头文件：

#import <UIKit/UIKit.h>

@interface GFSelectGroupViewController : UITableViewController
@property (weak, nonatomic) IBOutlet NSString *bodyText;
@end

最后接收视图控制器的实现文件（保存方法是我调用self.bodyText的地方，因为它认为bodytext为null，所以它出错了）：

#import "GFSelectGroupViewController.h"
#import <AFNetworking.h>
#import "GFCredentialStore.h"
#import "GFGroupResponseSerializer.h"

#define kBaseURL "http://someserver.com/"
#define kGroupURL "groups.json"
#define kPostURL "posts.json"

@interface GFSelectGroupViewController ()
@property (nonatomic, strong) NSArray *groups;
@property (strong, nonatomic) IBOutlet UITableView *tableView;
@property (weak, nonatomic) IBOutlet UIBarButtonItem *saveButton;
@end

@implementation GFSelectGroupViewController

- (id)initWithStyle:(UITableViewStyle)style
{
    self = [super initWithStyle:style];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    GFCredentialStore *credentialStore = [[GFCredentialStore alloc] init];

    NSString *authToken = [credentialStore authToken];
    NSLog(@"%@", authToken);

    __weak typeof(self)weakSelf = self;

    [self.saveButton setTarget:self];
    [self.saveButton setAction:@selector(save:)];

    NSString *urlString = [NSString stringWithFormat:@"%s%s", kBaseURL, kGroupURL];

    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    manager.responseSerializer = [GFGroupResponseSerializer serializer];
    [manager.requestSerializer setValue:authToken forHTTPHeaderField:@"auth_token"];
    NSLog(@"%@", manager.requestSerializer.HTTPRequestHeaders);
    [manager GET:urlString parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
        __strong typeof(weakSelf)strongSelf = weakSelf;
        strongSelf.groups = (NSArray *)responseObject;
        [strongSelf.tableView reloadData];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"Error: %@", error);
    }];
}

-(void)save:(id)sender {

    NSString * postURL = [NSString stringWithFormat:@"%s%s", kBaseURL, kPostURL];

    NSString *body = self.bodyText;
    NSLog(@"%@", body);

    NSDictionary *params = @{ @"post[body]" : body};


    AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager];
    [manager POST:postURL parameters:params success:^(AFHTTPRequestOperation *operation, id responseObject) {
        NSLog(@"JSON: %@", responseObject);
        [self dismissViewControllerAnimated:NO completion:nil];
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        NSLog(@"Error: %@", error);
    }];

}

iOS新手，所以任何帮助都非常感谢。感谢。

Answer 1

问题出在财产申报中。您将字符串声明为weak（和IBOutlet，它也不应该这样。）

在ARC规则下，只要所有强指针不再指向它，就会从内存中删除此对象。因为您在prepareForSegue方法中设置了它，所以在访问它之前它会被清零。因此，请将您的财产声明更改为：

@interface GFSelectGroupViewController : UITableViewController
@property (strong, nonatomic) NSString *bodyText;
@end

在prepareForSegue方法中，设置如下：

...
GFSelectGroupViewController *destViewController = segue.destinationViewController;

destViewController.bodyText = [self.bodyTextField.text copy];
...

还可以帮助自己进行调试，在viewDidLoad GFSelectGroupViewController方法中打印变量，以便正确复制它。

准备segue NSString成为NSObject？

1 个答案: