Question

所以我试图通过编程方式从一个视图控制器转换到另一个视图控制器，这样我只能在用户需要登录时初始化它。但是，xcode一直给我一个错误，它不在视图层次结构中，并拒绝加载它。

ViewController.h

#import <UIKit/UIKit.h>

@interface ViewController : UIViewController

@end

ViewController.m

#import "ViewController.h"
#import "API.h"

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];
    if (![[API sharedInstance] isAuthorized]) {
        [self performSegueWithIdentifier:@"ShowLogin" sender:nil];
    }// Do any additional setup after loading the view, typically from a nib.
}

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

@end

LoginScreen.h（控制器不在层次结构中）

#import <UIKit/UIKit.h>

@interface LoginScreen : UIViewController
{
    //the login form fields
    IBOutlet UITextField *fldUsername;
    IBOutlet UITextField *fldPassword;
}

//action for when either button is pressed
-(IBAction)btnLoginRegisterTapped:(id)sender;

@end

LoginScreen.m（控制器显然不在层次结构中）

#import "LoginScreen.h"
#import "UIAlertView+error.h"
#import "API.h"
#include <CommonCrypto/CommonDigest.h>

#define kSalt @"(protected value)"

@implementation LoginScreen

-(void)viewDidLoad {
    [super viewDidLoad];

}

#pragma mark - View lifecycle

- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation
{
    // Return YES for supported orientations
    return (interfaceOrientation == UIInterfaceOrientationPortrait);
}

-(IBAction)btnLoginRegisterTapped:(UIButton*)sender {
    //form fields validation
    if (fldUsername.text.length < 4 || fldPassword.text.length < 4) {
        [UIAlertView error:@"Enter username and password over 4 chars each."];
        return;
    }
    //salt the password
    NSString* saltedPassword = [NSString stringWithFormat:@"%@%@", fldPassword.text, kSalt];
    //prepare the hashed storage
    NSString* hashedPassword = nil;
    unsigned char hashedPasswordData[CC_SHA1_DIGEST_LENGTH];
    //hash the pass
    NSData *data = [saltedPassword dataUsingEncoding: NSUTF8StringEncoding];
    if (CC_SHA1([data bytes], [data length], hashedPasswordData)) {
        hashedPassword = [[NSString alloc] initWithBytes:hashedPasswordData length:sizeof(hashedPasswordData) encoding:NSASCIIStringEncoding];
    } else {
        [UIAlertView error:@"Password can't be sent"];
        return;
    }
    //check whether it's a login or register
    NSString* command = (sender.tag==1)?@"register":@"login";
    NSMutableDictionary* params =[NSMutableDictionary dictionaryWithObjectsAndKeys:command, @"command", fldUsername.text, @"username", hashedPassword, @"password", nil];
    //make the call to the web API
    [[API sharedInstance] commandWithParams:params onCompletion:^(NSDictionary *json) {
        //result returned
        NSDictionary* res = [[json objectForKey:@"result"] objectAtIndex:0];
        if ([json objectForKey:@"error"]==nil && [[res objectForKey:@"IdUser"] intValue]>0) {
            [[API sharedInstance] setUser: res];
            [self.presentingViewController dismissViewControllerAnimated:YES completion:nil];
            //show message to the user
            [[[UIAlertView alloc] initWithTitle:@"Logged in" message:[NSString stringWithFormat:@"Welcome %@",[res objectForKey:@"username"]] delegate:nil cancelButtonTitle:@"Close" otherButtonTitles: nil] show];
        } else {
            //error
            [UIAlertView error:[json objectForKey:@"error"]];
        }
    }];

}

@end

API.h（调用我的Web服务）

#import "AFHTTPClient.h"
#import "AFNetworking.h"

typedef void (^JSONResponseBlock)(NSDictionary* json);

@interface API : AFHTTPClient

@property (strong, nonatomic) NSDictionary* user;

+(API*)sharedInstance;
//check whether there's an authorized user
-(BOOL)isAuthorized;
//send an API command to the server
-(void)commandWithParams:(NSMutableDictionary*)params onCompletion:(JSONResponseBlock)completionBlock;
-(NSURL*)urlForImageWithId:(NSNumber*)IdPhoto isThumb:(BOOL)isThumb;

@end

API.m（调用我的Web服务）

#import "API.h"

//the web location of the service
#define kAPIHost @"(protected web address)"
#define kAPIPath @""

@implementation API

@synthesize user;

#pragma mark - Singleton methods
/**
 * Singleton methods
 */
+(API*)sharedInstance {
    static API *sharedInstance = nil;
    static dispatch_once_t oncePredicate;
    dispatch_once(&oncePredicate, ^{
        sharedInstance = [[self alloc] initWithBaseURL:[NSURL URLWithString:kAPIHost]];
    });

    return sharedInstance;
}

#pragma mark - init
//intialize the API class with the deistination host name

-(API*)init {
    //call super init
    self = [super init];
    if (self != nil) {
        //initialize the object
        user = nil;
        [self registerHTTPOperationClass:[AFJSONRequestOperation class]];
        // Accept HTTP Header; see http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
        [self setDefaultHeader:@"Accept" value:@"application/json"];
    }
    return self;
}

-(BOOL)isAuthorized {
    return [[user objectForKey:@"IdUser"] intValue]>0;
}

-(void)commandWithParams:(NSMutableDictionary*)params onCompletion:(JSONResponseBlock)completionBlock {
    NSData* uploadFile = nil;
    if ([params objectForKey:@"file"]) {
        uploadFile = (NSData*)[params objectForKey:@"file"];
        [params removeObjectForKey:@"file"];
    }

    NSMutableURLRequest *apiRequest = [self multipartFormRequestWithMethod:@"POST" path:kAPIPath parameters:params constructingBodyWithBlock: ^(id <AFMultipartFormData>formData) {
        if (uploadFile) {
            [formData appendPartWithFileData:uploadFile name:@"file" fileName:@"photo.jpg" mimeType:@"image/jpeg"];
        }
    }];
    AFJSONRequestOperation* operation = [[AFJSONRequestOperation alloc] initWithRequest: apiRequest];
    [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
        //success!
        completionBlock(responseObject);
    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
        //failure :(
        completionBlock([NSDictionary dictionaryWithObject:[error localizedDescription] forKey:@"error"]);
    }];
    [operation start];
}

-(NSURL*)urlForImageWithId:(NSNumber*)IdPhoto isThumb:(BOOL)isThumb {
    NSString* urlString = [NSString stringWithFormat:@"%@/%@upload/%@%@.jpg", kAPIHost, kAPIPath, IdPhoto, (isThumb)?@"-thumb":@""];
    return [NSURL URLWithString:urlString];
}

@end

Answer 1

问题是，在调用viewDidLoad时，初始视图控制器的视图尚未添加到窗口中。

将该通话移至viewDidAppear:

-(void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    if (![[API sharedInstance] isAuthorized]) {
        [self performSegueWithIdentifier:@"ShowLogin" sender:self];
    }
}

视图控制器不在视图层次结构中

1 个答案: