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

Foundation中的字典是由键-值对组成的数据集合，好比java中的Map，在字典对象中key值必须是唯一的，另外字典对象中的键和值都不能为nil。，如果要在字典对象中表示一个空值，可以用NSNull对象（这里主要指值value）。字典对象也可分为不可变字典和可变字典。

1、不可变字典

        NSNumber *num1 = [NSNumber numberWithInt:5];
        NSNumber *num2 = [NSNumber numberWithInt:10];
        NSNumber *num3 = [NSNumber numberWithInt:15];
        //初始化一个字典
        NSDictionary *dictionary = [NSDictionary dictionaryWithObject:num1 forKey:@"num"];
        //通过键获取值
        NSObject *object = [dictionary objectForKey:@"num"];
        
        
        NSDictionary *moreNum = [NSDictionary dictionaryWithObjectsAndKeys:num1,@"num1", num2,@"num2",num2,@"num3",nil];
        //将字典对象的key转化成一个枚举对象，用于遍历
        NSEnumerator *enumerater = [moreNum keyEnumerator];
        //获取所有的键
        NSArray *keyArray = [moreNum allKeys];
        //获取所有的值
        NSArray *valueArray = [moreNum allValues];
        
        
        //创建一个新字典，新字典包含其他字典
        NSDictionary *newDic = [NSDictionary dictionaryWithDictionary:dictionary];
        
        
        //获取字典数量
        NSInteger *theNum = [newDic count];

2、可变字典NSMutableDictionary

同样继承自NSDictionary,所以NSDictionary中的所有方法都适用于他

//创建一个可变字典
        NSMutableDictionary *mDic = [NSMutableDictionary dictionaryWithObjectsAndKeys:num1,@"num1", num2,@"num2",num2,@"num3",nil];
        //向可变字典对象中加入整个字典
        NSDictionary *dic2 = [NSDictionary dictionaryWithObject:@"nihao" forKey:@"hello"];
        [mDic addEntriesFromDictionary:dic2];
        
        //向可变字典中追加一个键值对
        [mDic setValue:@"jimGreen" forKey:@"name"];
        
        //遍历对象,取数据
        for(id key in mDic){
            
            id obj = [mDic objectForKey:key];
            NSLog(@"%@",obj);
            
        }