如何查看NSUserdefaults是否为零？

Question

嗯，我不知道我的标题是否草拟得很好，但我会尽力解释我的问题，我想在NSUserDefaults中为IndexPath保存一个NSDate，这发生在viewWillDisappear但是它崩溃时，它的保存正确，因为当我重新打开DatePicker加载我想要的日期，但保存日期在UserDefaults 时仍然崩溃因此，继承人我的代码，所以你可以看到发生了什么事......

我读如果NSUserDefaults是零或不，所以我可以加载DatePicker的：

NSArray *indexParams = [self.userdefaults objectForKey:@"indexpath"]; 
NSIndexPath *myIndexPath = [NSIndexPath indexPathForRow:indexParams[1] 
               inSection:indexParams[0]]; 

self.notificationDate = [self.userdefaults objectForKey:@"date"]; 
NSDate *date = [self.userdefaults objectForKey:[NSString stringWithFormat:@"%d", myIndexPath.row]]; 

if(date){ 
    [self.NotSwith setOn:YES]; 
    self.DatePicker.date = [self.userdefaults objectForKey:[NSString stringWithFormat:@"%d", myIndexPath.row]]; 



}else{ 
    [self.NotSwith setOn:NO]; 


    } 

当我要保存日期在viewWillDisappear其当崩溃发生：

NSArray *indexParams = [self.userdefaults objectForKey:@"indexpath"]; 
NSIndexPath *myIndexPath = [NSIndexPath indexPathForRow:indexParams[1] 
               inSection:indexParams[0]]; 

NSDate *date = [self.userdefaults objectForKey:[NSString stringWithFormat:@"%d", myIndexPath.row]]; 

if(date){ 
// [self.userdefaults synchronize]; 


} 

else{ 
    [self.userdefaults setObject:self.DatePicker.date forKey:[NSString stringWithFormat:@"%d", myIndexPath.row]]; 
    [self.userdefaults synchronize]; 
    [[UIApplication sharedApplication] scheduleLocalNotification:local]; 


} 

但成功保存的信息和日期选择器在重新启动时加载日期。

崩溃日志：

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[__NSPlaceholderArray initWithObjects:count:]: attempt to insert nil object from objects[0]' 

所以希望我解释好，谢谢！

设置indexpath：

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath{ 



    NSNumber *section = [NSNumber numberWithInt:indexPath.section]; 
    NSNumber *rows = [NSNumber numberWithInt:indexPath.row]; 

    [self.userdefaults setObject:@[section, rows] forKey:@"indexpath"]; 
} 

Answer 1

听起来像是你想节省选定的指数路径和日期。在NSUserDefaults中保存日期很简单。

// no need to keep a property on self for user defaults. you don't need to keep 
// that around. just a stack variable will work. 
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; 
NSDate *date = [NSDate date]; 

[defaults setObject:date forKey:@"myDate"]; 
[defaults synchronize]; 

拿回来以后是这样的：

NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults]; 
NSDate *date = [defaults objectForKey:@"myDate"]; 

// if nothing has been stored using that key then objectForKey will return nil 
if (date) { 
    // it's there! 
} else { 
    // it's not there 
} 

存储的索引路径是一个小更棘手，但是这将工作：

// wrap your row and section in NSNumbers, wrap those in an array for brevity 
NSNumber *section = [NSNumber numberWithInt:myIndexPath.section]; 
NSNumber *row = [NSNumber numberWithInt:myIndexPath.row]; 

[defaults setObject:@[section, row] forKey:@"myIndexPath"]; // then synchronize 

// naturally, when you get it later, you can check for nil again, and, 
// if it's not nil, to rebuild the index path... 

NSArray *indexParams = [defaults objectForKey:@"myIndexPath"]; 
NSIndexPath *myIndexPath = [NSIndexPath indexPathForRow:indexParams[1] 
               inSection:indexParams[0]]; 

的关键是什么ISN” t在这个答案中：没有NSData，没有NSKeyedArchiver，没有字符串操作来构建索引路径表示。祝你好运。