如何在Objective-C中过滤自定义对象

Question

I have a custom object which contains data as:

@interface Students : NSObject
{

}
@property (nonatomic,strong) NSString   *ID;
@property (nonatomic,strong) NSString   *FirstName;
@property (nonatomic,strong) NSString   *MiddleName;
@property (nonatomic,strong) NSString   *LastN

I want to filter it according to the last name. For example: I want an array which contains all the details of students having last name="Cena"

I tried this:

NSMutableArray *arrayToFilter = self.studentList;
NSString *nameformatString = @"LastName contains[c] a";
NSPredicate *namePredicate = [NSPredicate predicateWithFormat:nameformatString];

[arrayToFilter filterUsingPredicate:namePredicate];

When I run my app I am getting this error and my app crashes:

Terminating app due to uncaught exception 'NSUnknownKeyException', reason: 
'[< Students 0x7fd25e102d20> valueForUndefinedKey:]: 
this class is not key value coding-compliant for the key a.'

I am only able to get last name in array but I know this is wrong. How can I sort the custom object based on last name.

Code I am using to get lastName:

  names = [[NSMutableArray alloc]init];
for (int i = 0; i < [self.studentList count] ; i++)
{
    Students * studentsObj = (Students*)[self.studentList objectAtIndex:i];

    [names addObject:studentsObj.LastName];
}

Answer 1

Update the predicate to ,

NSString *textToMatch = @"a";
NSPredicate *namePredicate = [NSPredicate predicateWithFormat:@"LastN CONTAINS[cd] %@", textToMatch];

then

NSMutableArray *arrayToFilter = self.studentList;
NSArray *filteredArray = [arrayToFilter filteredArrayUsingPredicate:namePredicate];

for getting last name only,

NSArray *lastNames = [filteredArray valueForKey:@"LastN"];
NSArray *sortedArray = [lastNames sortedArrayUsingSelector:@selector(localizedCaseInsensitiveCompare:)];