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

2.1 创建一个空字典

NSDictionary *dictionary = [NSDictionary dictionary];

2.2 创建并初始化

// dictionaryWithObject:(id)forkey:(id)nscopying>
NSDictionary *dictionary1 = [NSDictionary dictionaryWithObject:@"IOS" forKey:@"Android"];
NSLog(@"%@", dictionary1);

2.3 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);

2.4 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);
//allkeys 返回一个数组包含词典中所有的键
NSLog(@"allkeys：%@", [dictionary5 allKeys]);

2.5 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]);

2.6allValues：返回一个数组包含词典中所有的值

NSLog(@"allValues：%@", [dictionary5 allValues]);

2.7 objectForKey：返回指定 key 的 value，若没有这个 key 返回 nil.

NSLog(@"%@", [dictionary5 objectForKey:@"name"]);

2.8 valueForKey 同样是返回指定 key 的 value

NSLog(@"%@", [dictionary5 valueForKey:@"name"]);

2.9 count：返回字典中的记录数

NSLog(@"count:%zi", [dictionary5 count]);

2.10 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);
}

2.11 遍历字典中的value

for (id key in dictionary5) {
    NSLog(@"%@", [dictionary5 valueForKey:key]);
}

2.12 可变字典

NSMutableDictionary * dictionary2 = [NSMutableDictionary dictionary];

2.13 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);

2.14 removeObjectForKey 删除词典中指定key对应的记录

[dictionary2 removeObjectForKey:@"100"];
NSLog(@"%@", dictionary2);

2.15 removeAllObjects 删除词典中的所有记录

[dictionary2 removeAllObjects];
NSLog(@"%@", dictionary2);

2.16 isEqualToDictionary 比较两个字典

NSDictionary * dictionary1 = [NSDictionary dictionaryWithObjectsAndKeys:
                           @"IOS", @"Name",
                           @15, @"Age",nil];
NSDictionary * dictionary2 = [NSDictionary dictionaryWithObjectsAndKeys:
                           @"Android", @"Name",
                           @28, @"Age",nil];
if([dictionary1 isEqualToDictionary:dictionary2]){ NSLog(@"dictionary1 equal dictionary2"); }else{ NSLog(@"dictionary1 not equal dictionary2"); } 

2.17 writeToFile 把字典写入文件(xml格式)

NSString * path = @"/Users/caile/dictionary1.xml"; [dictionary1 writeToFile:path atomically:YES];

2.18 dictionaryWithContentsOfFile 读取一个文件返回给新的字典对象

NSDictionary *newDic = [NSDictionary dictionaryWithContentsOfFile:path];