iOS NSDictionary

字典里面的排序

    {
    NSDictionary * numsDic = @{@(2):@"second",
                               @(1):@"first",
                               @(3):@"thrid"};
    NSDictionary * strDic = @{@"mark_1":@"first",
                              @"mark_3":@"thrid",
                              @"mark_2":@"second"};
   //针对的是NSString类型的value,@selector(compare:)其实是调用的NSString里面的方法，所以在此不用实现，不过可以在NSSting的分类中重写，用于测试使用。
    NSArray * numsSortedKeys = [numsDic keysSortedByValueUsingSelector:@selector(compare:)];
    NSArray * strSortedKyes = [strDic keysSortedByValueUsingComparator:^NSComparisonResult(id obj1, id obj2) {
        NSString * str1 = obj1;
        NSString * str2 = obj2;
        return [str1 compare:str2];
    }];
    NSLog(@"%@",numsSortedKeys.description);
    NSLog(@"%@",strSortedKyes.description);
    
    }

字典里的过滤

    NSDictionary * numsDic = @{@(2):@"second",
                               @(1):@"first",
                               @(3):@"thrid"};
    NSSet * filteredKyes = [numsDic keysOfEntriesPassingTest:^BOOL(id key, id obj, BOOL *stop) {
        BOOL result = NO;
        NSNumber * numKey = key;
        if (numKey.integerValue > 2) {
            result =  YES;
        }
        return result;
    }];
    NSLog(@"%@",filteredKyes.description); //结果时key值：3

        //这是一个很好的对字典进行过滤的方法,返回keys的集合，这些keys符合参数block的约束，在block内部在特定的条件下返回yes，返回的这个集合会保留当前遍历到那个字典对象的信息
        //        - (NSSet *)keysOfEntriesPassingTest:(BOOL (^)(id key, id obj, BOOL *stop))predicate NS_AVAILABLE(10_6, 4_0);

objectsForKeys:notFoundMarker:示例：没有对应的value的时候设置特定的mark.

    {
        NSArray *keyArr = @[@"k1", @"k2", @"k3"];
        NSArray *objArr = [NSArray arrayWithObjects:@"v1", @"v2", @"v3", nil];
        NSArray *srcArr = [NSArray arrayWithObjects:@"k0", @"k2", nil];
        NSDictionary *dict = [NSDictionary dictionaryWithObjects:objArr forKeys:keyArr];
//         NSArray *resArr = [dict objectsForKeys:srcArr notFoundMarker:@"not found"]; // ("not found", v2)
        NSArray *resArr = [dict objectsForKeys:srcArr notFoundMarker:[NSNull null]]; // ("", v2)
        
        NSLog(@"%@",resArr); //结果：("", v2)
    }

针对url的参数解析成字典

        NSString* wxNASAURLPath = @"http://weixin.sogou.com/weixin?type=2&ie=utf-8&query=NASA%E5%8F%91%E7%8E%B0%E6%96%B0%E5%9C%B0%E7%90%83";
        NSURLComponents* wxNASAURLComponents =  [NSURLComponents componentsWithString:wxNASAURLPath];
        NSMutableDictionary* queryItemDict = [NSMutableDictionary dictionary];
        NSArray* queryItems = wxNASAURLComponents.queryItems;
        for (NSURLQueryItem* item in queryItems) {
            [queryItemDict setObject:item.value forKey:item.name];
        }
        NSLog(@"queryItemDict = %@", queryItemDict);
    }