ios - Objective-C中的“使用未声明的标识符”错误

Question

我一直在遵循有关使用Xcode解析json的教程，但是遇到了我无法解决的问题。我怀疑他们是因为本教程使用的是5.1而我使用的是6.1

AppDelegate.m
未使用的变量'navController'
使用未声明的标识符“navController”
见下文

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPhone" bundle:nil];
        UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController: self.viewController];
    } else {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPad" bundle:nil];
        UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController: self.viewController];
    }
    self.window.rootViewController = navController;
    [self.window makeKeyAndVisible];
    return YES;
}

ViewController.m
预期方法主体
使用未声明的标识符“theData”

- (void)connection:NSURLConnection *)connection didReceiveData:(NSData *)theData
{
    [data appendData:theData];
}

Answer 1

您需要在if语句之外声明navController:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    UINavigationController* navController;

    navController = nil;
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPhone" bundle:nil];
        navController = [[UINavigationController alloc] initWithRootViewController: self.viewController];
    } else {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPad" bundle:nil];
        navController = [[UINavigationController alloc] initWithRootViewController: self.viewController];
    }
    self.window.rootViewController = navController;
    [self.window makeKeyAndVisible];
    return YES;
}

作为替代方案，您可以移动 navController的创建，因此只需要在一个地方完成:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone) {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPhone" bundle:nil];
    } else {
        self.viewController = [[ViewController alloc] initWithNibName:@"ViewController_iPad" bundle:nil];
    }
    self.window.rootViewController = [[UINavigationController alloc] initWithRootViewController: self.viewController];
    [self.window makeKeyAndVisible];
    return YES;
}

对于另一个错误，您在NSURLConnection之前缺少'('。

- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)theData
{
    [data appendData:theData];
}