黑马程序员_IOS开发_Objective-C学习笔记_字典

字典

1.字典（dictionary）是由键-对象对组成的数据集合。在与字典中超找单词定义一样，可以通过对象的键从Objective-C字典中获取需要的值（即那个对象）。字典中的键必须是单值的，通常他们是字符串，但也可以是其他对象类型。和键关联的值可以是任意对象类型，但不能是nil。

2.练习代码

//1.dictionary  创建一个空字典
NSDictionary *dictionary = [NSDictionary dictionary];

//2.创建并初始化
//  dictionaryWithObject:(id)forkey:(id)nscopying>
NSDictionary *dictionary1 = [NSDictionary dictionaryWithObject:@"IOS" forKey:@"Android"];
NSLog(@"%@", dic1);

//3.创建并返回一个字典。
// dictionaryWithObjects:forkeys
NSArray * keys = [NSArray arrayWithObjects:@"name", @"sex", @"age", nil];
NSArray * values = [NSArray arrayWithObjects:@"Apple", @"Android", [NSNumber numberWithInt:25], nil];
NSDictionary * dictionary3 = [NSDictionary dictionaryWithObjects:values forKeys:keys];
NSLog(@"%@", dictionary3);

//4.使用键-对象对{key1,obj1}、{key2,obj2}...创建词典
//  dictionaryWithObjectsAndKeys
NSDictionary * dictionary4 = [NSDictionary dictionaryWithObjectsAndKeys:
                       @"IOS", @"name",
                       @25,      @"age", nil];
NSLog(@"%@", dictionary4);//5.allkeys 返回一个数组包含词典中所有的键
NSLog(@"allkeys：%@", [dictionary5 allKeys]);

//6.allkeysForObject: 返回一个数组，包含所有对应到给定对象的关键字。
NSArray * aa = @[@"name",@"IOS",@"WinPhone",@"Android"];
NSLog(@"aaaaaaa%@", [dictionary5 allKeysForObject:aa]);

//7.allValues：返回一个数组包含词典中所有的值
NSLog(@"allValues：%@", [dictionary5 allValues]);

//8.objectForKey：返回指定 key 的 value，若没有这个 key 返回 nil.
NSLog(@"%@", [dictionary5 objectForKey:@"name"]);

//9.valueForKey 同样是返回指定 key 的 value。
NSLog(@"%@", [dictionary5 valueForKey:@"name"]);//10.count：返回字典中的记录数
NSLog(@"count:%zi", [dictionary5 count]);

//11.遍历字典中的key
NSLog(@"遍历字典\n\n");//快速遍历
for (id key in dictionary5) {
    NSLog(@"%@", key);
}
//遍历字典中的value
for (id key in dictionary5) {
    NSLog(@"%@", [dictionary5 valueForKey:key]);
}//12.可变字典
NSMutableDictionary * dictionary2 = [NSMutableDictionary dictionary];

//13.setObject: forKey: 添加value与key，如果key存在则替换该值
[dictionary2 setValue:@"itheima" forKey:@"first"];
[dictionary2 setValue:@"itcast" forKey:@"second"];
NSLog(@"%@", dictionary2);

//14.removeObjectForKey 删除词典中指定key对应的记录
[dic2 removeObjectForKey:@"100"];
NSLog(@"%@", dictionary2);

//15.removeAllObjects 删除词典中的所有记录
[dic2 removeAllObjects];
NSLog(@"%@", dictionary2);

NSDictionary * diction1 = [NSDictionary dictionaryWithObjectsAndKeys:
                           @"IOS", @"Name",
                           @15, @"Age",nil];
NSDictionary * diction2 = [NSDictionary dictionaryWithObjectsAndKeys:
                           @"Android", @"Name",
                           @28, @"Age",nil];

//16.isEqualToDictionary 比较两个字典
if([diction1 isEqualToDictionary:diction2]){
    NSLog(@"diction1 equal diction2");
}else{
    NSLog(@"diction1 not equal diction2");
}

//17.writeToFile 把字典写入文件(xml格式)
NSString * path = @"/Users/caile/diction1.xml";
[diction1 writeToFile:path atomically:YES];

//18.dictionaryWithContentsOfFile 读取一个文件返回给新的字典对象
NSDictionary *newDic = [NSDictionary dictionaryWithContentsOfFile:path];