Question

自学iOS编程，并从this book开始。我遇到错误“Property'MainViewController'找不到'AppDelegate *'类型的对象。

我已经检查过双倍和三倍，我正确地遵循了代码，甚至从头开始重新启动。我已经搜索了StackOverflow并尝试了一些解决方案，但没有一个工作，很少有正确匹配我的问题。有什么帮助吗？

AppDelegate.m（错误所在）

#import "AppDelegate.h"
#import "WeatherForecast.h"
#import "MainViewController.h"

@implementation AppDelegate

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    WeatherForecast *forecast = [[WeatherForecast alloc] init];
    self.MainViewController.forecast = forecast;
    // Override point for customization after application launch.
    MainViewController *controller = (MainViewController *)self.window.rootViewController;
    controller.managedObjectContext = self.managedObjectContext;
    return YES;
}

MainViewController.h

#import "FlipsideViewController.h"
#import "WeatherForecast.h"

#import <CoreData/CoreData.h>

@interface MainViewController : UIViewController <FlipsideViewControllerDelegate>

- (IBAction)showInfo;
- (IBAction)refreshView:(id) sender;
- (void)updateView;

@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (strong, nonatomic) WeatherForecast *forecast;

@end

Answer 1

问题应该出在application:didFinishLaunchingWithOptions的第二行。 self.MainViewController期待AppDelegate中的属性。只需删除此行并在controller.forecast = forecast;之前添加return YES.此时您将获得对MainViewController的引用并可以安全地设置属性（假设MainViewController通过Storyboard或XIB设置为当前的rootViewController）

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{    
   WeatherForecast *forecast = [[WeatherForecast alloc] init];
   // Override point for customization after application launch.
   MainViewController *controller = (MainViewController *)self.window.rootViewController;
   controller.managedObjectContext = self.managedObjectContext;
   controller.forecast = forecast;
   return YES;
}

错误：对象“AppDelegate *”上缺少属性

1 个答案: