我一直试图弄清楚为什么这不起作用但没有运气：
我正在Xcode中创建一个IOS应用程序并将其设置为：我首先从 ViewControllerA （LoginViewController）转到 ViewControllerB （HomeViewController）。在此segue期间，我传递一个UIImage和一个UILabel，以便在ViewControllerB中显示。一旦发生这种情况，我想设置另一个prepareForSegue转到 ViewControllerC （ProfileViewController）并再次传递相同的数据。但是，每次我尝试这样做时，应用程序都会出现故障，崩溃或死机。我不太清楚为什么会这样。
我希望每次我想传递数据时都有一种方法我不必做一个prepareForSegue - 比如Global Variable或Singleton。 但是我试图避免使用这两个选项，因为我已经多次读过这些选项是危险的，不应该真正使用。 如果这些方式中的任何一种都适用于此，那么请务必告诉我，这将是它的结束。
同时，我想知道是否有人可以帮助我理解为什么会出现这种错误。这是我的ViewControllerA.m代码：
LoginViewController.m
#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);
//dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^(void){
self.profilePicture.profileID = user.objectID;
self.lblUsername.text = user.name;
self.lblEmail.text = [user objectForKey:@"email"];
// 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];
//[_invisible sendActionsForControlEvents:UIControlEventTouchUpInside];
[self performSegueWithIdentifier:@"showMap" sender:self];
//});
//});
}
-(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 = [[UIImage alloc] init];
homeviewController.homepic = profPicture;
homeviewController.username = self.lblUsername;
}
@end
现在这是我的ViewControllerB代码：
HomeViewController.m
#import "HomeViewController.h"
#import "LoginViewController.h"
#import "ProfileViewController.h"
@interface HomeViewController ()
@end
@implementation HomeViewController
@synthesize homeviewpic, homepic, sendpic, homeViewUsername, username;
- (void)viewDidLoad {
[super viewDidLoad];
//----------Profile Picture---------------------------------------
// Determine the context of where to set image.
UIGraphicsBeginImageContext(self.homeviewpic.frame.size);
[homepic drawInRect:self.homeviewpic.bounds];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
// Create subview to be added
UIImageView *backgroundView = [[UIImageView alloc] initWithImage:image];
// Add subview
[self.homeviewpic addSubview:backgroundView];
[self.homeviewpic setContentMode:UIViewContentModeScaleAspectFill];
sendpic = homepic;
//----------Username-----------------------------------------------
//homeViewUsername.text = username.text;
// Do any additional setup after loading the view.
}
-(void)viewWillAppear:(BOOL)animated{
[super viewWillAppear: animated];
self.homeViewUsername.text = self.username.text;
}
- (void)didReceiveMemoryWarning {
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
//-----------------------------Screenshot of background void method--------------------------------
- (UIImage *) screenshot {
UIGraphicsBeginImageContextWithOptions(self.view.bounds.size, NO, [UIScreen mainScreen].scale);
[self.view drawViewHierarchyInRect:self.view.bounds afterScreenUpdates:YES];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return image;
}
//-------------------------------------------------------------------------------------------------
#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 {
ProfileViewController *PVC = segue.destinationViewController;
//PVC.profPic = sendpic;
//PVC.profileViewUsername = username;
}
@end
就目前而言，我已经在prepareForSegue中注释了这些行 - 这些行是问题的根源。如果有人可以帮助解释并尝试提供解决方案，我将非常感激。谢谢！
答案 0 :(得分：0)
您尝试在dispatch_async中显示两个viewcontrollers。 presentViewController和performSegueWithIdentifier做同样的事情。您必须放置一些条件，以便在dispatch_async方法中调用其中一个条件。试图呈现两个viewcontrollers将崩溃。