iphone - 从核心数据中获取时， float 变为 0.0000

Question

我创建了一个带有 float 属性的实体并将其值设置为 0.5

+(void)createSportNamed:(NSString *)name withContext:(NSManagedObjectContext *)context{
Sport *newSport = [NSEntityDescription insertNewObjectForEntityForName:@"Sport" inManagedObjectContext:context];
    newSport.name = name;
    newSport.maxRep = [NSNumber numberWithInt:45];
    newSport.endurance = [NSNumber numberWithFloat:0.5f];
    NSLog(@"endurance at set = %f",[newSport.endurance floatValue]);

NSError *saveError = nil;
[context save:&saveError];
}

从log来看，float的值还是0.5000

但是当我稍后获取它时，值不知何故变成了 0.0000

-(NSArray*)createWorkoutForSport:(NSString*)sportName withContext:(NSManagedObjectContext*)context{

NSFetchRequest *request = [NSFetchRequest new];
request.entity = [NSEntityDescription entityForName:@"Sport" inManagedObjectContext:context];
NSPredicate *sportNamePredicate = [NSPredicate predicateWithFormat:@"name == %d",sportName];
request.predicate = sportNamePredicate;
NSError *err = nil;
NSArray *results = [context executeFetchRequest:request error:&err];
Sport *theFetchedSport = [results lastObject];

int totalRep = [[theFetchedSport maxRep]intValue];
float endure = [[theFetchedSport endurance]floatValue];
int set;
NSLog(@"Endurance = %f",endure);

Answer 1

+(void)createSportNamed:(NSString *)name withContext:(NSManagedObjectContext *)context{
  Sport *newSport = [NSEntityDescription insertNewObjectForEntityForName:@"Sport" inManagedObjectContext:context];
  newSport.name = name;

这清楚地表明您的 Sport 实体的“名称”字段是一个字符串。

[NSPredicate predicateWithFormat:@"name == %d",sportName]

然而在这里你使用的是 %d，这意味着 int。您正在将字符串指针转换为 int。您应该使用 %@。因此，您的提取请求返回一个空数组，-lastObject 返回 nil，这意味着 [nil endurance] 也是 nil，这意味着 [[nil endurance] floatValue] 也是 nil，即 0。