Applications are expected to have a root view controller...?

Discussion in 'iOS Programming' started by chrono1081, Jan 26, 2012.

  1. chrono1081 macrumors 604


    Jan 26, 2008
    Isla Nublar
    Hi guys,

    Sorry for the strange title its too long to fit in there.

    I was following along in the Big Nerd Ranch Objective-C book and I ran into an issue and I haven't found the solution on the books forums or on Stack Overflow, and I think its in part because I don't understand the error. (I haven't touched Cocoa in a long time so its almost like its new to me again).

    Here is the issue:

    I run a program, it works fine even if I open and close it, however, if I kill it from the task manager and I reopen it I get this error:

    "Applications are expected to have a root view controller at the end of application launch"

    From researching, it looks like this error can stem from two places, the main.m file and the appdelegate.m file in the method:

    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
    The code is typed correctly from the book but I don't know enough about Cocoa to know how to fix it. Can anyone help me understand what this error stems from and how to fix it?

    Here is my main.m file:

    int main(int argc, char *argv[])
        @autoreleasepool {
            return UIApplicationMain(argc, argv, nil, NSStringFromClass([BNRAppDelegate class]));
    Here is my AppDelegate file:

    #import "BNRAppDelegate.h"
    //Helper function to fetch the path to our to-do data stored on disk
    NSString *docPath(void)
        NSArray *pathList = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
        return [[pathList objectAtIndex:0] stringByAppendingPathComponent:@""];
    @implementation BNRAppDelegate
    @synthesize window = _window;
    -(void) addTask:(id)sender
        //Get the to-do item
        NSString *t = [taskField text];
        //Quit here if the taskField is empty
        if([t isEqualToString:@""])
        //Add it to our working array
        [tasks addObject:t];
        //Refresh thetable so that the new item shows up
        [taskTable reloadData];
        //And clear our the text field
        [taskField setText:@""];
        //Dismiss the keyboard
        [taskField resignFirstResponder];
    #pragma mark - Application delegate callbacks
    - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
        //Attempt to load an existing to-do dataset from an array stored to disk
        NSArray *plist = [NSArray arrayWithContentsOfFile:docPath()];
            //If there was a dataset available, copy it to our instance variable
            tasks = [plist mutableCopy];
            //Otherwise, jsut create an empty one to get us started
            tasks = [[NSMutableArray alloc] init];
        //Is tasks empty?
        if([tasks count] == 0)
            //Put some strings in it
            [tasks addObject:@"Walk the dogs"];
            [tasks addObject:@"Feed the hogs"];
            [tasks addObject:@"Chop the logs"];
        //Create and configure the UIWindow instance
        //A CGRect is a struct with an origin (x,y) and size (width,height)
        CGRect windowFrame = [[UIScreen mainScreen] bounds];
        UIWindow *theWindow = [[UIWindow alloc] initWithFrame: windowFrame];
        [self setWindow:theWindow];
        //Define the frame rectangles of the three UI elements
        //CGRectMake() creates a CHRect from (x, y, width, height)
        CGRect tableFrame  = CGRectMake(0, 80, 320, 380);
        CGRect fieldFrame  = CGRectMake(20, 40, 200, 31);
        CGRect buttonFrame = CGRectMake(228, 40, 72, 31);
        //Create and configure the table view
        taskTable = [[UITableView alloc] initWithFrame: tableFrame
        [taskTable setSeparatorStyle:UITableViewCellSeparatorStyleNone];
        //Make this object the table view's dataSource
        [taskTable setDataSource:self];
        //Create and configure the text field where new tasks will be types
        taskField = [[UITextField alloc] initWithFrame: fieldFrame];
        [taskField setBorderStyle:UITextBorderStyleRoundedRect];
        [taskField setPlaceholder:@"Type a task, tap Insert"];
        //Create and configure a rounded rect Insert button
        insertButton = [UIButton buttonWithType:UIButtonTypeRoundedRect];
        [insertButton setFrame:buttonFrame];
        //Buttons behave using a target/action callback
        //Configure the Insert button's action to call this object's -addTask: method
        [insertButton addTarget:self 
        //Give the button a title
        [insertButton setTitle:@"Insert"
        //Add our three UI elements to the window
        [[self window] addSubview:taskTable];
        [[self window] addSubview:taskField];
        [[self window] addSubview:insertButton];
        //Finalize the window and put it on the screen
        [[self window] setBackgroundColor: [UIColor whiteColor]];
        [[self window] makeKeyAndVisible];
        return YES;
    #pragma mark - Table View Management
    -(NSInteger)tableView:(UITableView *)tableView 
        //Because this tableview only has one section, the number of rows
        //in it is equal to the number of items in our tasks array
        return [tasks count];
    -(UITableViewCell *)tableView:(UITableView *)tableView 
            cellForRowAtIndexPath:(NSIndexPath *)indexPath
        //To improve performance, we reconfigure cells in memory
        //that have scrolled off screen and hand them back
        //with the new contents instead of always creating new cells.
        //First we check to see if there's a cell available for reuse.
        UITableViewCell *c = [taskTable dequeueReusableCellWithIdentifier:@"Cell"];
            //...and only allocate a new cell if none are available
            c = [[UITableViewCell alloc] initWithStyle:UITableViewCellStyleDefault reuseIdentifier:@"Cell"];
        //Then we (re)configure the cell based on the model object, 
        //in this case our todoItems array
        NSString *item = [tasks objectAtIndex:[indexPath row]];
        [[c textLabel] setText:item];
        //and hand back to the table view the properly configured cell
        return c;
    - (void)applicationWillResignActive:(UIApplication *)application
         Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
         Use this method to pause ongoing tasks, disable timers, and throttle down OpenGL ES frame rates. Games should use this method to pause the game.
    - (void)applicationDidEnterBackground:(UIApplication *)application
        //Save array to disk (iOS4+ only)
        [tasks writeToFile:docPath() atomically:YES];
    - (void)applicationWillEnterForeground:(UIApplication *)application
         Called as part of the transition from the background to the inactive state; here you can undo many of the changes made on entering the background.
    - (void)applicationDidBecomeActive:(UIApplication *)application
         Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
    - (void)applicationWillTerminate:(UIApplication *)application
        //iOS 3 or below
        //Save our array to disk
        [tasks writeToFile:docPath() atomically:YES];

    Now, when I kill the program from the task manager and reopen I get this:

    "Thread 1: Program received signal: "SIGKILL". and the line:

    return UIApplicationMain(argc, argv, nil, NSStringFromClass([BNRAppDelegate class]));
    in main.m is highlighted.

    Sorry for the long post but I didn't want to not include anything. Can someone please explain why my program crashes like this? The last question about this on the books forum went unanswered : /
  2. jnoxx macrumors 65816


    Dec 29, 2010
    Aartselaar // Antwerp // Belgium
    First of all, debugger can't handle it if you close the app while connected via xcode, and reboot it again, it will send u a sigkill, it's not your code, it's the debugger :) so you will have to just deal with that sadly enough.
    About the applications expected to have a rootController.
    You are just adding subviews to your mainwindow instead of setting the rootViewController (of where the app should start), to the mainwindow. That's why it's guesing there is no rootController.
    Simple as that actually :)
    I think you can do.
    [self.window setRoot(lala)];
  3. chrono1081 thread starter macrumors 604


    Jan 26, 2008
    Isla Nublar
    Thanks so much! Its been driving me nuts trying to figure that out :)

    Its been two years roughly since I touched Cocoa Touch so I'm relearning it all over again :/

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