Objective-c的Foundation中常用類4——字典NSDictionary、NSMutableDictionary

Foundation中的字典是由鍵-值對組成的資料集合，好比java中的Map，在字典對象中key值必須是唯一的，另外字典對象中的鍵和值都不能為nil。，如果要在字典對象中表示一個空值，可以用NSNull對象（這裡主要指值value）。字典對象也可分為不可變字典和可變字典。

1、不可變字典

        NSNumber *num1 = [NSNumber numberWithInt:5];        NSNumber *num2 = [NSNumber numberWithInt:10];        NSNumber *num3 = [NSNumber numberWithInt:15];        //初始化一個字典        NSDictionary *dictionary = [NSDictionary dictionaryWithObject:num1 forKey:@"num"];        //通過鍵擷取值        NSObject *object = [dictionary objectForKey:@"num"];                        NSDictionary *moreNum = [NSDictionary dictionaryWithObjectsAndKeys:num1,@"num1", num2,@"num2",num2,@"num3",nil];        //將字典對象的key轉化成一個枚舉對象，用於遍曆        NSEnumerator *enumerater = [moreNum keyEnumerator];        //擷取所有的鍵        NSArray *keyArray = [moreNum allKeys];        //擷取所有的值        NSArray *valueArray = [moreNum allValues];                        //建立一個新字典，新字典包含其他字典        NSDictionary *newDic = [NSDictionary dictionaryWithDictionary:dictionary];                        //擷取字典數量        NSInteger *theNum = [newDic count];

2、可變字典NSMutableDictionary

同樣繼承自NSDictionary,所以NSDictionary中的所有方法都適用於他

//建立一個可變字典        NSMutableDictionary *mDic = [NSMutableDictionary dictionaryWithObjectsAndKeys:num1,@"num1", num2,@"num2",num2,@"num3",nil];        //向可變字典對象中加入整個字典        NSDictionary *dic2 = [NSDictionary dictionaryWithObject:@"nihao" forKey:@"hello"];        [mDic addEntriesFromDictionary:dic2];                //向可變字典中追加一個索引值對        [mDic setValue:@"jimGreen" forKey:@"name"];                //遍曆對象,取資料        for(id key in mDic){                        id obj = [mDic objectForKey:key];            NSLog(@"%@",obj);                    }