如何获取数组中字典的值的索引

Question

an array like this:

  <array> <dict> <key>Place</key> <string>A</string> <key>Name</key> <string>B</string> <key>Object</key> <string>C</string> </dict> <dict> <key>Place</key> <string>D</string> <key>Name</key> <string>E</string> <key>Object</key> <string>F</string> </dict> <dict> <key>Place</key> <string>X</string> <key>Name</key> <string>Y</string> <key>Object</key> <string>Z</string> </dict> <dict> <key>Place</key> <string>S</string> <key>Name</key> <string>T</string> <key>Object</key> <string>U</string> </dict> ... </array> 

// for some reason, I simplified levels of this sample by removing original top level array. Now they look like an array composed of some dictionaries.

for instance, can got any value via [[objectArray objectAtIndex:i] valueForKey:@"Place"] , if like X,

then, in another place still in same .m , need to ONLY leverage X to reversely get what's index of the dictionary where X is. Because in this place, only the objectArray is able to be accessed.

What's right method that's supposed to do?

Answer 1

Use KVC again!

3 lines when you have the array :D

short

NSArray *arrayWithDicts = @[d1,d2,d3,d4];//your array!

NSArray *arrayWithPlaces = [arrayWithDicts valueForKey:@"Place"];
NSUInteger index = [arrayWithPlaces indexOfObject:@"cologne"];
NSDictionary *dict = index != NSNotFound ? arrayWithDicts[index] : nil;

full example

#import <Foundation/Foundation.h>

int main(int argc, char *argv[]) {
    @autoreleasepool {
        //build demo array
        NSDictionary *d1 = @{@"Place": @"clackson"};
        NSDictionary *d2 = @{@"Place": @"berlin"};
        NSDictionary *d3 = @{@"Place": @"cologne"};
        NSDictionary *d4 = @{@"Place": @"mclean"};
        NSArray *arrayWithDicts = @[d1,d2,d3,d4];

        //get all places
        NSArray *arrayWithPlaces = [arrayWithDicts valueForKey:@"Place"];
        assert(arrayWithDicts.count == arrayWithPlaces.count);

        //find place and get dict
        NSUInteger index = [arrayWithPlaces indexOfObject:@"cologne"];
        NSDictionary *dict = index != NSNotFound ? arrayWithDicts[index] : nil;

        NSLog(@"%@", dict);     
    }
}

Answer 2

You need to loop over the outer array, and in that loop you need to loop over the inner array, looking for the dictionary whose value for @"Place" is X . Here's one way to do it:

@implementation NSArray (StackOverflow)

- (NSIndexPath *)indexPathOfDictionaryWithPlace:(NSString *)place {
    // I can't refer directly to an array inside a block, so I have to add an extra variable.
    NSUInteger indexStorage[2];
    NSUInteger *indexes = indexStorage;

    indexes[0] = [self indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
        NSArray *subarray = obj;
        indexes[1] = [subarray indexOfObjectPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
            NSDictionary *dictionary = obj;
            return [place isEqualToString:dictionary[@"Place"]];
        }];
        return indexes[1] != NSNotFound;
    }];

    if (indexes[0] == NSNotFound) {
        return nil;
    } else {
        return [NSIndexPath indexPathWithIndexes:indexes length:2];
    }
}

@end