除非单击 UIButton，否则不会加载数据

Question

这可能是一个奇怪的案例，如果我的问题或解决方案不清楚，我提前道歉：

我有一个 LoginViewController 可以获取用户的 Facebook 个人资料图片、用户名、电子邮件等。然后我将它转到 HomeViewController 显示一些对象、其他项目和显示用户个人资料图片的 UIView。

奇怪部分是我创建的 UIImage 仅在我使用 UIButton 时被传输。我似乎无法通过任何其他方式将图像发送到 HomeViewController。我什至设置了一个 GCP 让它尝试等待 Facebook 提供信息 - 仍然没有。下面是我为 LoginViewController.m 编写的代码。如果有人知道为什么会这样，我将非常感激。谢谢！

#import "LoginViewController.h"
#import <QuartzCore/QuartzCore.h>


@interface LoginViewController ()

- (void)toggleHiddenState:(BOOL)shouldHide;

@end

@implementation LoginViewController

@synthesize profPicture;


- (void)viewDidLoad {
    [super viewDidLoad];

    [self toggleHiddenState:YES];
    self.lblLoginStatus.text = @"";

    self.loginButton.readPermissions = @[@"public_profile", @"email"];
    self.loginButton.delegate = self;

    // Do any additional setup after loading the view.
}

-(void)toggleHiddenState:(BOOL)shouldHide{
    self.lblUsername.hidden = shouldHide;
    self.lblEmail.hidden = shouldHide;
    self.profilePicture.hidden = shouldHide;
    self.loggedinwallpaper.hidden = shouldHide;
    self.FBlogout.hidden = shouldHide;
}


-(void)loginViewShowingLoggedInUser:(FBLoginView *)loginView{
    self.lblLoginStatus.text = @"";

    [self toggleHiddenState:NO];
}

-(void)loginViewShowingLoggedOutUser:(FBLoginView *)loginView{
    self.lblLoginStatus.text = @"";

    [self toggleHiddenState:YES];
}

-(void)loginViewFetchedUserInfo:(FBLoginView *)loginView user:(id<FBGraphUser>)user{
    NSLog(@"%@", user);
    self.profilePicture.profileID = user.objectID;
    self.lblUsername.text = user.name;
    self.lblEmail.text = [user objectForKey:@"email"];
    dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^(void){
        // Create Facebook Profile Picture from User ID url
        NSString *pic_link = [NSString stringWithFormat:@"http://graph.facebook.com/%@/picture?width=300&height=300", user.objectID];
        NSURL *pic_url = [NSURL URLWithString:pic_link];
        profPicture = [UIImage imageWithData: [NSData dataWithContentsOfURL:pic_url]];

        dispatch_async(dispatch_get_main_queue(), ^(void){
            //Main Thread : UI Updates
            UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
            UIViewController *homeViewController = (UIViewController *)[storyboard instantiateViewControllerWithIdentifier:@"HomeViewController"];
            [self performSelector:@selector(prepareForSegue:sender:) withObject:nil afterDelay:1.0 ];
            [self presentViewController:homeViewController animated:YES completion:nil];


        });
    });
}

-(void)loginView:(FBLoginView *)loginView handleError:(NSError *)error{
    NSLog(@"%@", [error localizedDescription]);
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Navigation

// In a storyboard-based application, you will often want to do a little preparation before navigation
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    HomeViewController *homeviewController = segue.destinationViewController;
    homeviewController.homepic = profPicture;
}


@end

Answer 1

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    HomeViewController *homeviewController = segue.destinationViewController;
    homeviewController.homepic = [UIImage alloc] init];
    homeviewController.homepic = profPicture;
}

Answer 2

根据您共享的代码，我假设您提到的按钮有效，因为您使用 segue 将其连接到 Storyboard 中，对吗？（拖了一个箭头到下一个VC？）

您的代码的问题在于此处

[self performSelector:@selector(prepareForSegue:sender:) withObject:nil afterDelay:1.0 ];

你在没有必要参数的情况下自行触发 prepareForSegue:sender: - 你没有准备好转场，因为你甚至没有转场到另一个视图控制器。所以执行HomeViewController *homeviewController = segue.destinationViewController;时segue为nil所以无法设置图片

您应该可以通过将在主线程上运行的代码替换为以下内容来解决此问题：

dispatch_async(dispatch_get_main_queue(), ^(void){
    // Main Thread : UI Updates
    [self performSegueWithIdentifier:@"<insert segue identifier here>" sender:self];
});

确保在 Storyboard 中为视图控制器之间的 segue 设置名称，并在此处使用该标识符。（见Apple Docs）

除非单击 UIButton，否则不会加载数据

Data Doesn't Load Unless UIButton Clicked

objective-c

uibutton

grand-central-dispatch

facebook-graph-api

segue