How to search an NSSet or NSArray for an object which has an specific value for an specific property?

问题

Example: I have an NSSet with 20 objects, and every object has an type property. I want to get the first object which has [theObject.type isEqualToString:@"standard"].

I remember that it was possible to use predicates somehow for this kind of stuff, right?

回答1:

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"type == %@", @"standard"];
NSArray *filteredArray = [myArray filteredArrayUsingPredicate:predicate];
id firstFoundObject = nil;
firstFoundObject =  filteredArray.count > 0 ? filteredArray.firstObject : nil;

NB: The notion of the first found object in an NSSet makes no sense since the order of the objects in a set is undefined.

回答2:

You can get the filtered array as Jason and Ole have described, but since you just want one object, I'd use - indexOfObjectPassingTest: (if it's in an array) or -objectPassingTest: (if it's in a set) and avoid creating the second array.

回答3:

Generally, I use indexOfObjectPassingTest: as I find it more convenient to express my test in Objective-C code rather than NSPredicate syntax. Here's a simple example (imagine that integerValue was actually a property):

NSArray *array = @[@0,@1,@2,@3];
NSUInteger indexOfTwo = [array indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
    return ([(NSNumber *)obj integerValue] == 2);
}];
NSUInteger indexOfFour = [array indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
    return ([(NSNumber *)obj integerValue] == 4);
}];
BOOL hasTwo = (indexOfTwo != NSNotFound);
BOOL hasFour = (indexOfFour != NSNotFound);
NSLog(@"hasTwo: %@ (index was %d)", hasTwo ? @"YES" : @"NO", indexOfTwo);
NSLog(@"hasFour: %@ (index was %d)", hasFour ? @"YES" : @"NO", indexOfFour);

The output of this code is:

hasTwo: YES (index was 2)
hasFour: NO (index was 2147483647)

回答4:

NSArray* results = [theFullArray filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF.type LIKE[cd] %@", @"standard"]];

来源：https://stackoverflow.com/questions/3076477/how-to-search-an-nsset-or-nsarray-for-an-object-which-has-an-specific-value-for

标签

iphone

objective-c

nsarray

nspredicate

nsset