来自NSMutableDictionary的键的值不打印

Question

我正在学习Stephen Kochan的“Objective-C编程”，我遇到了NSDictionary的可变副本问题。 所以，这里是我的代码：

NSMutableString *value1 = [[NSMutableString alloc ] initWithString: @"Value for Key one" ]; 
    NSMutableString *value2 = [[NSMutableString alloc ] initWithString: @"Value for Key two" ]; 
    NSMutableString *value3 = [[NSMutableString alloc ] initWithString: @"Value for Key three" ]; 
    NSMutableString *value4 = [[NSMutableString alloc ] initWithString: @"Value for Key four" ]; 
    NSString *key1 = @"key1"; 
    NSString *key2 = @"key2"; 
    NSString *key3 = @"key3"; 
    NSString *key4 = @"key4"; 

    NSDictionary *dictionary = [[NSDictionary alloc] initWithObjectsAndKeys: value1, key1, value2, key2, value3, key3, nil]; 

    NSDictionary *dictionaryCopy = [[NSDictionary alloc] init]; 
    NSMutableDictionary *dictionaryMutableCopy = [[NSMutableDictionary alloc] init]; 

    dictionaryCopy = [dictionary copy]; 
    dictionaryMutableCopy = [dictionary mutableCopy]; 

    [value1 setString: @"New value for Key one" ]; 
    [value2 setString: @"New value for Key two" ]; 
    [value3 setString: @"New value for Key three" ]; 

    dictionaryMutableCopy[key4] = value4; 

    NSLog(@"All key for value 4"); 

    for (NSValue *key in [dictionaryMutableCopy allKeysForObject:value4]) { 
     NSLog(@"key: %@", key); 
    } 

    NSLog(@"All values"); 

    for (NSValue *val in [dictionaryMutableCopy allValues]) { 
     NSLog(@"value: %@", val); 
    } 

    for (NSValue *key in [dictionaryMutableCopy allKeys]) { 
     NSLog(@"Key: %@ value: %@", key, dictionary[key]); 
    } 

你怎么看

，我打印从我NSMutableDictionary所有键/值代码的目的，而是key 4我没有价值！

Screen from terminal

但是你可以看到如何在价值key 4岂不等于空！

[Content of NSMutableDictionary][2] 

什么问题？请帮助

Answer 1

在最后for循环，你是从dictionary而不是dictionaryMutableCopy所获得的价值：

for (NSValue *key in [dictionaryMutableCopy allKeys]) { 
    NSLog(@"Key: %@ value: %@", key, dictionaryMutableCopy[key]); 
    //        ^^^^^^^^^^^^^^^^^^^^^ 
}