如何显示登录屏幕之前的根视图控制器(PFQueryTableViewController)尝试查询没有用户和崩溃的程序

Question

我希望我正在工作的程序的根视图控制器是PFQueryTableViewController，但是，我需要该应用程序确保用户在PFQueryTableViewController尝试查询之前登录。

我尝试创建一个RootTabBarViewController，其初始视图是PFQueryTableViewController，并在RootTabBarViewController的。h和。m文件中放入以下内容:

//
//  RootTabBarViewController.h
//
#import <UIKit/UIKit.h>
#import <Parse/Parse.h>
@interface RootTabBarViewController : UITabBarController <PFLogInViewControllerDelegate, PFSignUpViewControllerDelegate>
@end

//
//  RootTabBarViewController.m
//
#import "RootTabBarViewController.h"
#import "PlannrLogInViewController.h"
@interface RootTabBarViewController ()
@end
@implementation RootTabBarViewController
- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}
- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view.
}
- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}
- (void)viewDidAppear:(BOOL)animated
{
    [super viewDidAppear:animated];
    if (![PFUser currentUser]) { // No user logged in
        // Create the log in view controller
        PFLogInViewController *logInViewController = [[PFLogInViewController alloc] init];
        [logInViewController setDelegate:self]; // Set ourselves as the delegate
        // Create the sign up view controller
        PFSignUpViewController *signUpViewController = [[PFSignUpViewController alloc] init];
        [signUpViewController setDelegate:self]; // Set ourselves as the delegate
        // Assign our sign up controller to be displayed from the login controller
        [logInViewController setSignUpController:signUpViewController];
        // Present the log in view controller
        [self presentViewController:logInViewController animated:YES completion:NULL];
    }
}
/*
#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
{
    // Get the new view controller using [segue destinationViewController].
    // Pass the selected object to the new view controller.
}
*/
#pragma mark - PFLoginViewController Delegate
// Sent to the delegate to determine whether the log in request should be submitted to the server.
- (BOOL)logInViewController:(PFLogInViewController *)logInController shouldBeginLogInWithUsername:(NSString *)username password:(NSString *)password {
    // Check if both fields are completed
    if (username && password && username.length != 0 && password.length != 0) {
        return YES; // Begin login process
    }
    [[[UIAlertView alloc] initWithTitle:@"Missing Information"
                                message:@"Make sure you fill out all of the information!"
                               delegate:nil
                      cancelButtonTitle:@"ok"
                      otherButtonTitles:nil] show];
    return NO; // Interrupt login process
}
// Sent to the delegate when a PFUser is logged in.
- (void)logInViewController:(PFLogInViewController *)logInController didLogInUser:(PFUser *)user {
    [self dismissViewControllerAnimated:YES completion:NULL];
}
// Sent to the delegate when the log in attempt fails.
- (void)logInViewController:(PFLogInViewController *)logInController didFailToLogInWithError:(NSError *)error {
    NSLog(@"Failed to log in...");
}
// Sent to the delegate when the log in screen is dismissed.
- (void)logInViewControllerDidCancelLogIn:(PFLogInViewController *)logInController {
    [self.navigationController popViewControllerAnimated:YES];
}
#pragma mark - PFSignUpViewController Delegate
// Sent to the delegate to determine whether the sign up request should be submitted to the server.
- (BOOL)signUpViewController:(PFSignUpViewController *)signUpController shouldBeginSignUp:(NSDictionary *)info {
    BOOL informationComplete = YES;
    // loop through all of the submitted data
    for (id key in info) {
        NSString *field = [info objectForKey:key];
        if (!field || field.length == 0) { // check completion
            informationComplete = NO;
            break;
        }
    }
    // Display an alert if a field wasn't completed
    if (!informationComplete) {
        [[[UIAlertView alloc] initWithTitle:@"Missing Information"
                                    message:@"Make sure you fill out all of the information!"
                                   delegate:nil
                          cancelButtonTitle:@"ok"
                          otherButtonTitles:nil] show];
    }
    return informationComplete;
}
// Sent to the delegate when a PFUser is signed up.
- (void)signUpViewController:(PFSignUpViewController *)signUpController didSignUpUser:(PFUser *)user {
    [self dismissModalViewControllerAnimated:YES]; // Dismiss the PFSignUpViewController
}
// Sent to the delegate when the sign up attempt fails.
- (void)signUpViewController:(PFSignUpViewController *)signUpController didFailToSignUpWithError:(NSError *)error {
    NSLog(@"Failed to sign up...");
}
// Sent to the delegate when the sign up screen is dismissed.
- (void)signUpViewControllerDidCancelSignUp:(PFSignUpViewController *)signUpController {
    NSLog(@"User dismissed the signUpViewController");
}
@end

这是我的。m文件为PFQueryTableViewController子类:

//
//  EventPFQueryTableViewController.m
//
#import "EventPFQueryTableViewController.h"
#import "Event.h"
@interface EventPFQueryTableViewController ()
@end
@implementation EventPFQueryTableViewController

- (id)initWithCoder:(NSCoder *)aDecoder{
    self = [super initWithCoder:aDecoder];
    if (self)
    {
        self.parseClassName = kEventListClassKey;
    }
    return self;
}
- (PFQuery *)queryForTable
{
    PFQuery *query = [Event query];
    [query whereKey:kEventListFieldKeyUser equalTo:[PFUser currentUser]];
    return query;
}
/*
@end

然而，这个选项卡栏视图控制器的viewDidLoad函数中的代码似乎没有在PFQueryTableViewController(根栏视图控制器的第一个视图)加载并尝试查询之前运行，因为我仍然得到异常:

2014-07-10 20:46:04.226 Plannr[12810:60b] *终止应用程序由于未捕获异常'NSInvalidArgumentException'，原因:'不能做比较查询类型:(null)'

我如何确保登录视图加载远在EventPFQueryTableViewController之前?

Answer 1

首先，你可以通过像这样修改EventPFQueryTableViewController的- (PFQuery *)queryForTable方法来防止应用程序崩溃:

if ([PFUser currentUser]) { //User logged in.
  PFQuery *query = [Event query];
  [query whereKey:kEventListFieldKeyUser equalTo:[PFUser currentUser]];
  return query;
}
else {
  [super objectsDidLoad:error]; //Return failed to turn off spinner.
  return nil;
}

你还想在你的PFQueryTableViewController中为登录事件设置一个通知监听器。这个会在用户登录更新表视图时调用比如handleLogIn:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(handleLogIn:) name:kLoggedInEvent object:nil];

在你的PFQueryTableViewController中添加handleLogIn方法:

- (void)handleLogIn:(NSNotification*) notification {
  [self loadObjects]
}

然后当注册/登录成功时，调用你创建的通知使TableView得到更新:

[[NSNotificationCenter defaultCenter] postNotificationName:kLoggedInEvent object:nil userInfo:nil];