ios - 如何查看 NSUserdefaults 是否为零？

Question

好吧，我不知道我的标题是否起草得好，但我会尝试解释我的问题是什么，我想在 NSUserDefaults 中为 IndexPath 保存一个 NSDate，这种情况发生在 viewWillDisappear 但崩溃时，它的保存正确，因为当我重新打开 DatePicker 时会加载我想要的日期，但在 UserDefaults 中保存日期时仍然崩溃这是我的代码，这样你就可以看到发生了什么......

我读取 NSUserDefaults 是否为零，以便我可以加载 DatePicker:

    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];


    }

当我想在崩溃发生时将日期保存在 viewWillDisappear 中时:

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];


}

但是信息已成功保存，并且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]'

希望我能解释清楚，谢谢!

设置索引路径:

- (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

听起来您想同时保存选定的索引路径和日期。在 NSUserDefaults 中保存日期很容易。

// 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];

稍后以这种方式取回:

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
}

存储索引路径有点棘手，但这会起作用:

// 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]];

关键是这个答案中没有的内容:没有 NSData，没有 NSKeyedArchiver，没有用于构建索引路径表示的字符串操作。祝你好运。