【语法】NSDictionary数据字典

参照练习nsdictionary

【1】字典的创建

//静态方法,不需要释放内存
NSDictionary *dit=[[NSDictionary alloc] init];
NSDictionary *dict=[NSDictionary dictionaryWithObject:@"v" forKey:@"k"];
NSLog(@"%@",dict);

2.

//最常用的初始化方式
dict=[NSDictionary dictionaryWithObjectsAndKeys:@"v1",@"k1",@"v2",@"k2",nil];
NSLog(@"%@",dict);

3.

NSArray *obkects=[NSArray arrayWithObjects:@"v1",@"v2",@"v3",nil];
NSArray *keys=[NSArray arrayWithObjects:@"k1",@"k2",@"k3", nil];
dict=[NSDictionary dictionaryWithObjects:obkects forKeys:keys];
NSLog(@"%@",dict);

【2】字典的使用

1.

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
//count是计算有多少个键值对；
NSLog(@"count=%zi",[dict count]);

2.

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
//这个是来查看键值的另外一个
//由于NSdictionary是不可变的，所以只能取值，不能修改值
id obj=[dict objectForKey:@"k2"];
NSLog(@"obj=%@",obj);

3.将字典写入文件中

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
NSString *path=@"/Users/haiyefeng/Desktop/test.txt";
[dict writeToFile:path atomically:YES];

4.

//读取文件中的字典。
NSString *path2=[NSDictionary dictionaryWithContentsOfFile:path];
NSLog(@"%@",path2);

【3】字典的用法2

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
NSArray *key= [dict allKeys];
NSLog(@"keys=%@",key);

2.

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
NSArray *objects=[dict allValues];
NSLog(@"%@",objects);

3.

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
objects= [dict objectsForKeys:[NSArray arrayWithObjects:@"k1",@"k2",@"k555",nil] notFoundMarker:@"not found"];//notfoundmarker里如果找不到的话，当key找不到对应的value时，用maker参数值代替
NSLog(@"objects=%@",objects);

【4】遍历字典

void dictFot(){

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
//遍历字典的所有key
for(id key in dict){
id value =[dict objectForKey:key];
NSLog(@"%@",value);

}

}

2.迭代器

NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];
//key 迭代器
NSEnumerator *enumer=[dict keyEnumerator];
id key =nil;
while (key=[enumer nextObject]){
id value =[dict objectForKey:key];
NSLog(@"%@=%@",key,value);

}

3.这里只提供方法

//对象迭代器
//[dict objectEnumerator];

4.

//遍历字典3
void dictFor3(){
NSDictionary *dict=[NSDictionary dictionaryWithObjectsAndKeys:
@"v1",@"k1",
@"v2",@"k2",
@"v3",@"k3",nil];

[dict enumerateKeysAndObjectsUsingBlock:
^(id key, id obj, BOOL *stop) {
NSLog(@"%@=%@",key,obj);
}];

}

我们不能在数组中放入nil值,因为NSArray和NSDicSonary中nil有特殊意义。 使用NSNull可以消除这种歧义。

NSMutableArray *array=[NSMutableArray array];
NSMutableDictionary *dict=[NSMutableDictionary dictionary];

NSNumber *number=[NSNumber numberWithInt:100];
[array addObject:number];
[dict setObject:number forKey:@"number"];

NSRect rect=NSMakeRect(1, 2, 30, 40);
NSValue *value=[NSValue valueWithBytes:&rect objCType:@encode(NSRect)];
[array addObject:value];
[dict setObject:value forKey:@"rect"];

[array addObject:[NSNull null]];
[dict setObject:[NSNull null] forKey:@"null"];

//输出
for (NSObject *item in array ) {
NSLog(@"%@",item);
}
NSLog(@"==========================");
for (NSString *key in dict) {
NSLog(@"%@=%@",key,[dict objectForKey:key]);
}