來自NSMutableDictionary的鍵的值不打印

我正在學習Stephen Kochan的「Objective-C編程」，我遇到了NSDictionary的可變副本問題。所以，這裏是我的代碼：來自NSMutableDictionary的鍵的值不打印

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]); 
    }

你怎麼看

，我打印從我NSMutableDictionary所有鍵/值代碼的目的，而是key 4我沒有價值！

Screen from terminal

但是你可以看到如何在價值key 4豈不等於空！

[Content of NSMutableDictionary][2]

什麼問題？請幫助

來源

2016-02-05 Nikita Bonachev

在最後for循環，你是從dictionary而不是dictionaryMutableCopy所獲得的價值：

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

來源

2016-02-05 10:15:40 trojanfoe

哦，非常感謝！我知道這將是一個愚蠢的錯誤！ –

@NikitaBonachev使用'NSValue'的BTW對我而言並不常見。我從來沒有用過它;如果你知道鍵是字符串，那麼使用'NSString'是正常的。我想你正在學習一個教程，但請牢記這一點。 – trojanfoe

好的，感謝您的解決方案和建議。 –

來自NSMutableDictionary的鍵的值不打印

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