通过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

我试图对用自定义对象填充的NSArray进行排序。每个对象都有属性 startDateTime ，类型为NSDate。

以下代码产生一个数组， sortedEventArray ，填充但未排序。

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

解决方案

您确定 startDateTime 节点事件的实例变量是否为nil？

如果您还没有，您可以为您的节点添加（自定义） -description 事件对象，它执行这样的事情：

   - （NSString *）description {
 return [NSString stringWithFormat：@ ％@  - ％@，
 [super description]，startDateTime]];然后在你的排序代码中记录数组之前和之后：
 
  NSLog（@nodeEventArray ==％@，nodeEventArray）; 
 NSSortDescriptor * dateDescriptor = [NSSortDescriptor 
 sortDescriptorWithKey：@startDateTime
 Descending：YES]; 
 NSArray * sortDescriptors = [NSArray arrayWithObject：dateDescriptor]; 
 NSArray * sortedEventArray = [nodeEventArray 
 sortedArrayUsingDescriptors：sortDescriptors]; 
 NSLog（@sortedEventArray ==％@，sortedEventArray）; 
  
如果 startDateTime  code> nil ，则前后数组将具有相同的顺序（因为排序操作等于发送所有 -compare：消息到 nil ，基本上什么也不做）。
 
I am attempting to sort an NSArray that is populated with custom objects. Each object has a property startDateTime that is of type NSDate. 

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];

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

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]];
}
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);
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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