iPhone,如何存储一个值和一个键,并按键和索引查找?

NSMutableDictionary *sectionInfos;
NSMutableArray *sectionTitles;

NSDictionary *info = [sectionInfos objectForKey:sectionTitle];
int rowsCount = ((NSArray *)[info objectForKey:@"Countries"]).count;

NSString *title = [sectionTitles objectAtIndex:sectionIndex];
NSDictionary *info = [sectionInfos objectForKey:title];
int rowsCount = ((NSArray *)[info objectForKey:@"Countries"]).count;

[sectionInfos setObject:info forKey:sectionTitle];

[sectionTitles addObject:sectionTitle];

NSMutableDictionary *sectionRowCounts;
NSMutableArray *sectionTitles;

int rowCount = [[sectionRowCounts objectForKey:sectionTitle] intValue];

NSString *title = [sectionTitles objectAtIndex:sectionIndex];
int rowCount = [[sectionRowCounts objectForKey:title] intValue];

[sectionRowCounts setObject:[NSNumber numberWithInt:rowCount] forKey:sectionTitle];
[sectionTitles addObject:sectionTitle];

http://developer.apple.com/library/ios/#documentation/cocoa/reference/foundation/Classes/NSDictionary_Class/Reference/Reference.html#//apple_ref/occ/cl/NSDictionary

NSMutableDictionary

NSString *yourvalue = @"Hello!";
NSMutableDictionary *d;
[d setValue:yourvalue forKey:@"yourkey"];
NSString *retrievedvalue = [d valueForKey:@"yourkey"];
// you should get value here