按 NSDate 属性对自定义对象的 NSArray 进行排序 [英] Sort NSArray of custom objects by their NSDate properties

问题描述

我正在尝试对填充了自定义对象的 NSArray 进行排序.每个对象都有一个 NSDate 类型的属性 startDateTime.

I am attempting to sort an NSArray that is populated with custom objects. Each object has a property startDateTime that is of type NSDate.

以下代码生成一个数组，sortedEventArray，已填充但未排序.我是完全错误的方法还是我只是遗漏了一些小东西?

The following code results in an array, sortedEventArray, populated but not sorted. Am I going about this the completely wrong way or am I just missing something small?

NSSortDescriptor *dateDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"startDateTime" 
                                                                 ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:dateDescriptor];
NSArray *sortedEventArray = [nodeEventArray sortedArrayUsingDescriptors:sortDescriptors];

推荐答案

您确定节点事件的 startDateTime 实例变量非 nil 吗?

Are you sure that the startDateTime instance variables of the node events are non-nil?

如果您还没有，您可以向节点事件对象添加一个(自定义)-description 方法，该方法执行如下操作:

If you don't have one already, you might add a (custom) -description method to your node event objects that does something like this:

- (NSString *)description {
   return [NSString stringWithFormat:@"%@ - %@",
                   [super description], startDateTime]];
}

然后在您的排序代码中记录之前和之后的数组:

Then in your sorting code log the array before and after:

NSLog(@"nodeEventArray == %@", nodeEventArray);
NSSortDescriptor *dateDescriptor = [NSSortDescriptor
                                     sortDescriptorWithKey:@"startDateTime" 
                                                 ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:dateDescriptor];
NSArray *sortedEventArray = [nodeEventArray
         sortedArrayUsingDescriptors:sortDescriptors];
NSLog(@"sortedEventArray == %@", sortedEventArray);

如果 startDateTime 都是 nil，那么 before 和 after 数组将具有相同的顺序(因为排序操作将等同于发送所有 nil>-compare: 消息到 nil，基本上什么都不做.

If the startDateTime's are all nil, then the before and after arrays will have the same order (since the sorting operation will equate to sending all the -compare: messages to nil, which basically does nothing).

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