NSURL、NSURLComponent

[ShannonChenCHN]

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[ShannonChenCHN]

参考

• NSURL / NSURLComponents
• NSURL Class Reference
• URL- Wikipedia

[ShannonChenCHN]

NSURL 和 NSURLComponent

一、 NSURL

1. 简介

• What is NSURL:
  - represents an URL
• Usage
  - the location of a resource on a remote server
  - the path of a local file on disk
  - an arbitrary piece of encoded data
  - interapplication communication
• Structure of a URL
  - An NSURL object is composed of two parts
  - base URL
  - a string that is resolved relative to the base URL
  - Absolute URL and relative URL
  - Structure of a URL：
  最基础的表示法中，URI 由一个 scheme 和一个 hierarchical part 组成，带有 query 和 fragment（后两者非必需）：

<scheme name> : <hierarchical part> [ ? <query> ] [ # <fragment> ]

很多像HTTP的协议中会定义有一定的规范结构，例如：username、password、port, 以及hierarchical part 中的 path：

以 URL https://johnny:p4ssw0rd@www.example.com:443/script.ext;param=value?query=value#ref 为例，可以分解为以下几部分：

Components	Value
scheme	https
user	johnny
password	p4ssw0rd
host	www.example.com
port	443
path	/script.ext
pathExtension	ext
pathComponents	["/", "script.ext"]
parameterString	param=value
query	query=value
fragment	ref

二、 NSURLComponent

NSURL 和 NSURLComponents 的不同之处在于，URL component 属性是 readwrite 的。它提供了安全直接的方法来修改URL的各个部分。

另外，NSURLComponents 也有 readwrite 属性对每个 component 进行 [percent-encoded]。

NSURLComponents 的典型应用场景就是 URL 解析，获取其中的参数。

NSString *urlString = @"http://www.example.com/path/index.html?type=animal&name=panda#nose";
        
        NSURLComponents *components = [NSURLComponents componentsWithString:urlString];
        
        NSArray <NSURLQueryItem *> *queryItems = [components queryItems] ?: @[];
        NSMutableDictionary *queryParams = [NSMutableDictionary dictionary];
        for (NSURLQueryItem *item in queryItems) {
            if (item.value == nil) {
                continue;
            }
            
            if (queryParams[item.name] == nil) {
                // first time seeing a param with this name, set it
                queryParams[item.name] = item.value;
            } else if ([queryParams[item.name] isKindOfClass:[NSArray class]]) {
                // already an array of these items, append it
                NSArray *values = (NSArray *)(queryParams[item.name]);
                queryParams[item.name] = [values arrayByAddingObject:item.value];
            } else {
                // existing non-array value for this key, create an array
                id existingValue = queryParams[item.name];
                queryParams[item.name] = @[existingValue, item.value];
            }
        }
        
        NSLog(@"%@", queryParams);

FAQ

Q: How to deal with some special characters in an URL, like chinese?
A: Using percent-encoding.

NSString * encodingString = [urlString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];

If you want to retrieve the original characters in an url,

NSString *str = [model.album_name stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];