objective-c - NSManagedObjectContext在Core Data应用程序(iOS)中返回nil

Question

我试图在每次按下按钮时将字符串保存到数据库中，但是当我运行该项目时，会在控制台上找到它:'NSInvalidArgumentException', reason: '+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Info''。

关于数据模型，我创建了一个.xcdatamodel，其模型名为“Info”，其内部为名为“path”的属性，其类型为字符串。

我创建了三个函数。 “enterdata”通过调用“findData”检查名称是否可用。如果名称可用，则通过“newData”记录新数据，如果不是，则查找其他名称。

我一直在寻找一些类似的问题，并且发现了this。它说de ManagedObjectContext必须传递给View Controller，但我不明白这是什么意思。

这是我的.h代码:

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

这是我的.m代码:

#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

它确切地告诉您错误是什么:

nil不是合法的NSManagedObjectContext参数

这意味着在这一行上:

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

变量 context是 nil。这意味着您的 managedObjectContext方法无法正常工作。您没有显示此内容，因此我们可以添加的内容不多。