Core data 核心数据:不保存
保存到一个变量letsMeet.startTimeLabel时遇到问题。选择NSLog后立即显示正确的值,但是,在保存到另一个变量(letsMeet.endTimeLabel)后,letsMeet.startTimeLabel将更改为(NULL)。代码如下:Core data 核心数据:不保存,core-data,nsmanagedobjectcontext,save,Core Data,Nsmanagedobjectcontext,Save,保存到一个变量letsMeet.startTimeLabel时遇到问题。选择NSLog后立即显示正确的值,但是,在保存到另一个变量(letsMeet.endTimeLabel)后,letsMeet.startTimeLabel将更改为(NULL)。代码如下: - (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex { letsMeet = (LetsMeet *) [
- (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex
{
letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
switch (actionSheet.tag)
{
case 1:
{
if (buttonIndex == 0)
{
UIDatePicker *startDatePicker = (UIDatePicker *)[actionSheet viewWithTag:kDatePickerTag1];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"dd"];
NSDate *selectedDate = [startDatePicker date];
NSDateFormatter *dayFormatter = [[NSDateFormatter alloc] init];
[dayFormatter setDateFormat:@"EEEE"];
NSDate *selectedDay= [startDatePicker date];
NSDateFormatter *monthFormatter = [[NSDateFormatter alloc] init];
[monthFormatter setDateFormat:@"MMMM"];
NSDate *selectedMonth = [startDatePicker date];
NSString *date = [[NSString alloc] initWithFormat:@"%@", [dateFormatter stringFromDate:selectedDate]];
DateLabel.text = date;
[letsMeet setDateLabel:date];
NSString *month = [[NSString alloc] initWithFormat:@"%@", [dayFormatter stringFromDate:selectedMonth]];
MonthLabel.text = month;
[letsMeet setMonthLabel:month];
NSString *day = [[NSString alloc] initWithFormat:@"%@", [monthFormatter stringFromDate:selectedDay]];
DayLabel.text = day;
[letsMeet setDateLabel:day];
NSDateFormatter *timeFormatter = [[NSDateFormatter alloc] init];
[timeFormatter setDateFormat: @"h:mm a"];
NSDate *selectedStartTime = [startDatePicker date];
NSString *startTime = [[NSString alloc] initWithFormat:@"%@", [timeFormatter stringFromDate:selectedStartTime]];
StartTimeLabel.text = startTime;
[letsMeet setStartTimeLabel:startTime];
NSError *error = nil;
if (![managedObjectContext save:&error]){
NSLog(@"Error Saving");
}
}
NSLog (@"This is the StartTime after selecting %@", letsMeet.startTimeLabel);
}
break;
case 2:
{
if (buttonIndex == 0)
{
UIDatePicker *endTimePicker = (UIDatePicker *)[actionSheet viewWithTag:kDatePickerTag2];
NSDateFormatter *endTimeFormatter = [[NSDateFormatter alloc] init];
[endTimeFormatter setDateFormat: @"h:mm a"];
NSDate *endSelectedTime = [endTimePicker date];
NSString *endTime = [[NSString alloc] initWithFormat:@"%@", [endTimeFormatter stringFromDate:endSelectedTime]];
EndTimeLabel.text = endTime;
[letsMeet setEndTimeLabel:endTime];
NSLog (@"This is the EndTime %@", letsMeet.endTimeLabel);
NSLog (@"This is the StartTime after selecting BOTH %@", letsMeet.startTimeLabel);
}
else if (buttonIndex == 1)
{
EndTimeLabel.text = @"Whenever";
[letsMeet setEndTimeLabel:EndTimeLabel.text];
}
NSError *error = nil;
if (![managedObjectContext save:&error]) {
}
}break;
// Handle the error.
}
}
-(void) prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
UIViewController *destinationViewController = segue.destinationViewController;
NSLog (@"Prepare For Segue StartTime %@", letsMeet.startTimeLabel);
NSLog (@"Prepare For Segue EndTime%@", letsMeet.endTimeLabel);
}
以下是日志:
2013-02-20 21:38:24.253 AppointmentTime[3129:c07] This is the StartTime after selecting 9:30 AM
2013-02-20 21:38:32.325 AppointmentTime[3129:c07] This is the EndTime 12:15 PM
2013-02-20 21:38:32.325 AppointmentTime[3129:c07] This is the StartTime after Selecting BOTH (null)
2013-02-20 21:38:34.069 AppointmentTime[3129:c07] Prepare For Segue StartTime (null)
2013-02-20 21:38:34.069 AppointmentTime[3129:c07] Prepare For Segue EndTime12:15 PM
问:为什么letsMeet.startTimeLabel在第一次显示时是正确的,而在选择EndTime后,它会变为NULL。请注意,在prepareForSegue之前,EndTime始终显示正确的值。奇怪 根据您的日志和代码,您将进入开关块两次。这意味着您要输入两次
操作表:ClickedButtonIndex:
方法。所以每次你输入这个方法
letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
语句执行两次,然后创建两个对象。你可以通过从商店取货看到这一点
因此,您正在检查两个不同对象中的属性,从而检查null
如果只使用一个托管对象,则在执行insertNewObjectForEntityForName:inManagedObjectContext:
之前,可能可以为该对象添加一个nil
检查。这将确保您使用的是相同的对象如果同时使用多个对象,请使用对象id或某个唯一键来标识对象并对其进行操作 编辑:
您可以使用以下代码检查nil:
if(letsMeet==Nil){
letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
}
只有在调用actionSheet:ClickedButtonIndex:
方法的对象始终在内存中时,这才有效。但是,由于您正在持久化,您可能需要从存储中获取对象,然后检查对象的数量
NSError *error;
NSFetchRequest *request = [[NSFetchRequest alloc] init];
[request setEntity:[NSEntityDescription entityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext]];
NSArray *objectArray = [managedObjectContext executeFetchRequest:request error:&error]
if(objectArray.count==0){
letsMeet = (LetsMeet *) [NSEntityDescription insertNewObjectForEntityForName:@"LetsMeet" inManagedObjectContext:managedObjectContext];
}else{
letsMeet = (LetsMeet *)[objectArray objectAtIndex:0];
}
注意:如果您只需要保留几个变量,那么核心数据可能是一种过度消耗。请改用NSUserDefaults并保持简单。因为它们是不同的实例。您的意思是什么?我也在PrepareForSegue中为这两个变量做了NSLog,StartTime显示为NULL,而EndTime显示为正确的值。我更新了代码和日志。谢谢你的回复。我只使用了一个managedObject。你能给我举个例子,说明如何检查nil,以确保我使用的是同一个managedObject,我应该把它放在哪里?我试图检查nil,但它不起作用。我在if语句中做了一个NSLog,但它从未执行过。StartTime和EndTime的NSLog都显示为空。然后我尝试了你的获取代码。同样的事情也发生了。if语句中的NSLog也永远不会执行。不知道为什么会跳过if语句。我甚至试着在ViewDidLoad中移动这两个代码,得到了相同的结果。我应该尝试使用ObjectID吗?我不知道如何获得唯一的ObjectID。ThanksI还尝试仅将以下行移动到ViewDidLoad:letsMeet=(letsMeet*)[NSEntityDescription insertNewObjectForEntityForName:@“letsMeet”inManagedObjectContext:managedObjectContext];我得到了以下日志:2013-02-22 09:01:14.632任命时间[3140:c07]这是选择9:01 AM 2013-02-22 09:01:18.409任命时间[3140:c07]这是结束时间2013-02-22 09:01:18.410任命时间[3140:c07]这是选择两者后的开始时间(空)对不起。提供的解决方案中有一个错误。。不是莱斯米特=无但是letsMeet==零。如果变量为nil,则仅创建对象。我将更新答案。在fetch部分,如果它没有“if”块,则表示对象数组计数不是零。所以你已经有了一个对象。所以用那个物体。再次更新答案。