我想每一个按钮被按下时,以字符串保存到数据库中,但是当我运行该项目,我得到我的控制台上返回零。的NSManagedObjectContext核心数据应用(iOS)
参照数据模型,我已经创建与实体名为“信息”和,在其内部,命名为“路径”与一种类型的字符串的属性的.xcdatamodeld。
我已经创建了三个功能。 “enterdata”通过调用“findData”来检查名称是否可用。如果名称可用,则通过“newData”记录新数据,如果不是,则查找不同的名称。
我一直在寻找一些类似的问题,我已经发现了this。它说de ManagedObjectContext必须传递给View Controller,但我不明白它是什么意思。
这里是我的.h代码:
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
这里是我的.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;
}
}
其中d你是否创建了托管对象上下文? '[self managedObjectContext]'做什么?错误消息表明它返回'nil'。 –
在我的.h中有@属性(只读,强壮,非原子)NSManagedObjectContext * managedObjectContext;'它是在.m中合成的,所以它在理论上被声明。不是吗? – iosdevrocks
据* *声明的实例变量和属性,但该值是'nil'。您必须从核心数据模型和持久性存储创建托管对象上下文。也许你在'AppDelegate'或你的代码中的其他地方做过这些?然后你必须从那里使用托管对象上下文。 –