Question

I’m trying to save a string into a database every time a button is pressed but when I run the project, I get that on my console: 'NSInvalidArgumentException', reason: '+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Info''.

Referring to the Data Model, I have created a .xcdatamodeld with an Entity named ‘Info’ and, inside it, an attribute named ‘path’ with a type of string.

I’ve created three functions. “enterdata” Checks if the name is avaliable or not by calling “findData”. If the name is avaliable, a new data is recorded throught “newData”, if not, it looks for a different name.

I’ve been looking for some similar questions and I’ve found out this. It says that de ManagedObjectContext has to be passed to the View Controller but I don’t understand what does it mean.

Here’s my .h code:

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;

Here’s my .m code:

#import <CoreData/CoreData.h>

@synthesize managedObjectContext;

int  iSavedNum = 1;
bool bCanSave;

//Enter data
- (IBAction) enterdata:(id)sender {

    //Search if data is already registered
    NSString *docDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSString *path = [NSString stringWithFormat:@"%@/info%i.png",docDir, iSavedNum];
    [self findData:path :@"path"];

    //If data is already saved, save it with new name.
    if (bCanSave == NO) {
        for (iSavedNum = 1; bCanSave == YES; iSavedNum++) {
            [self findData:path :@"path"];
            if (bCanSave == YES) {
                [self newData:path :@"path"];
            }
        }
    } else {
        [self newData:path :@"path"];
    }

}

//Input new data
- (void) newData:(NSString *)value:(NSString *)key {

    //Create ManagedObjectContext and ManagedObjectModel
    __0AppDelegate *appDelegate = (__0AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = [appDelegate managedObjectContext];
    NSManagedObjectModel *newRecord;

    //Put the data to the Entity
    NSString *entityName = @"Info";
    newRecord = [NSEntityDescription insertNewObjectForEntityForName:entityName inManagedObjectContext:context];
    [newRecord setValue:value forKey:key];

    //Errors management and cheking
    NSError *error;
    [context save:&error];
    NSLog(@"Info Saved. Value: %@ Key: %@", value, key);

}

//Find Data
- (void) findData:(NSString *)valor:(NSString *)key {

    //Create ManagedObjectContext
    __0AppDelegate *appDelegate = (__0AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *context = [appDelegate managedObjectContext];

    //Call the Entity and make a request
    NSString *entityName = @"Info";
    NSEntityDescription *entityDesc = [NSEntityDescription entityForName:entityName inManagedObjectContext:context];
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    [request setEntity:entityDesc];

    //Create predicate to call specific info
    NSPredicate *pred = [NSPredicate predicateWithFormat:@"(%@ = %@)", key, valor];
    [request setPredicate:pred];

    //Errors management and creation of an array with found info
    NSError *error;
    NSArray *objects = [context executeFetchRequest:request error:&error];

    //Set if the name is avaliable or not
    if ([objects count] == 0) {
        bCanSave = YES;
    } else {
        bCanSave = NO;
    }
}

Answer 1

It tells you exactly what the error is:

nil is not a legal NSManagedObjectContext parameter

That means that on this line:

newRecord = [NSEntityDescription insertNewObjectForEntityForName:entityName
                                          inManagedObjectContext:context];

The variable context is nil. This means that your managedObjectContext method isn’t working correctly. You don’t show this so there’s not much more we can add.