在iOS 9.0之后，以前常用的NSString编码的方法stringByAddingPercentEscapesUsingEncoding:被弃用了，项目中可能会出现一堆如下⚠️：
'stringByAddingPercentEscapesUsingEncoding:' is deprecated: first deprecated in iOS 9.0 - Use -stringByAddingPercentEncodingWithAllowedCharacters: instead, which always uses the recommended UTF-8 encoding, and which encodes for a specific URL component or subcomponent since each URL component or subcomponent has different rules for what characters are valid.
作为一个有强迫症的优秀程序猿，表示不能忍！
文档里面是这么说的：
- (nullable NSString *)stringByAddingPercentEscapesUsingEncoding:(NSStringEncoding)enc
NS_DEPRECATED(10_0, 10_11, 2_0, 9_0, "Use -stringByAddingPercentEncodingWithAllowedCharacters: instead,
which always uses the recommended UTF-8 encoding, and which encodes for a specific URL component or subcomponent since each URL component or subcomponent has different rules for what characters are valid.");
很明白，用stringByAddingPercentEncodingWithAllowedCharacters:方法替换之。
这个方法官方文档是这么说的：
// Returns a new string made from the receiver by replacing all characters not in the allowedCharacters set with percent encoded characters. UTF-8 encoding is used to determine the correct percent encoded characters. Entire URL strings cannot be percent-encoded. This method is intended to percent-encode an URL component or subcomponent string, NOT the entire URL string. Any characters in allowedCharacters outside of the 7-bit ASCII range are ignored.
最后一句Any characters in allowedCharacters outside of the 7-bit ASCII range are ignored.，意思就是说，任何非7-bit ASCII字符搁到allowedCharacters里面也将被忽略，也就是allowedCharacters里面的字符跟7-bit ASCII字符不会被编码。
换句话说，上面方法在处理的时候会编码url的中的非7-bit ASCII字符，如这些【`#%^{}"[]|\<>】，如果需要忽略之，需要通过(NSCharacterSet *)allowedCharacters这个参数指定。总结如下
[aString stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
//等价于
[aString stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet characterSetWithCharactersInString:@"`#%^{}\"[]|\\<> "]];
注意：
- 字符集最后是一个空格！
- 这里字符集的意思就是，字符串中含有字符集里面的字符将不会被编码。
另外，URL中常用的NSCharacterSet类型定义在分类NSCharacterSet (NSURLUtilities)中，包含字符集如下：
URLHostAllowedCharacterSet "#%/<>?@\^`{|}
URLFragmentAllowedCharacterSet "#%<>[\]^`{|}
URLPasswordAllowedCharacterSet "#%/:<>?@[\]^`{|}
URLPathAllowedCharacterSet "#%;<>?[\]^`{|}
URLQueryAllowedCharacterSet "#%<>[\]^`{|}
URLUserAllowedCharacterSet "#%/:<>?@[\]^`
以上，还在等什么，全局搜索替换吧，消灭⚠️！
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