[IOS] 学习-NSDictionary （Object-c中的key-value）

NSDictionary类似Java中的Map，内部存储key-value对，key的类型是NSString，value可以是任意对象类型指针。键值和数据必须不为nil，如果想表示一个空的值，则用NSNull。字典本身是不可以更改的。NSMutableDictionary 是可更改的字典。
下面例子是网上流传的，写的很细

        NSArray *array1 = [NSArray arrayWithObjects:@"iphone",@"ipod",nil];
        NSArray *array2 = [NSArray arrayWithObjects:@"mac",@"imac",@"mac pro",nil];
        ////1、创建字典 ，类方法初始化自动释放
        NSDictionary *myDictionary = [NSDictionarydictionaryWithObjectsAndKeys:array1,@"mobile",array2,@"computers",nil];//注意用nil结束
        NSLog(@”myDictionary = %@”,myDictionary);
        //得到key-value的个数
        int dictSize = [myDictionary count];
        //根据key找到字典中的值
        NSArray *mobile = [myDictionary objectForKey:@"mobile"];
        //得到所有key
        NSArray *keys = [myDictionary allKeysForObject:array1];
        //得到所有value
        NSArray *values = [myDictionary allValues];
        //快速枚举
        for(id key in myDictionary)
        {
            NSLog(@”key: %@,value: %@”,key,[myDictionary objectForKey:key]);
        }
        //如果字典只包含属性列表对象(NSData,NSDate,NSNumber,NSString,NSArray或NSDictionary)可以保存到文件中
        NSString *filePath = [[[NSBundlemainBundle]resourcePath]stringByAppendingPathComponent:@”dict.txt”];
        BOOL success = [myDictionary writeToFile:filePath atomically:YES];
        //用文件填充
        NSDictionary *myDict2 =[NSDictionary dictionaryWithContentsOfFile:filePath];
        
        //可变字典
        NSMutableDictionary *dictMutable = [[NSMutableDictionaryalloc]initWithObjectsAndKeys:array1,@”mobile”,array2,@”computer”, nil];
        NSString *string4 = @”stringTV”;
        //修改对象
        [dictMutable setObject:string4 forKey:@"media"];
        //删除对象
        [dictMutable removeObjectForKey:@"mobile"];
        //删除多个对象
        NSArray *keyArray =[NSArray arrayWithObjects:@"mobile",@"computer", nil];
        [dictMutable removeObjectForKey:keyArray];
        //删除所有对象

        [dictMutable removeAllObjects];