NSMutableURLRequest 删除请求头Header

NSMutableURLRequest 删除、添加

1、看下NSMutableURLRequest的setValue: forHTTPHeaderField和addValue: forHTTPHeaderField两个方法注释如下，请看discussion说明:

/*! 
  
    @discussion  If a value was previously set for the given header
    field, that value is replaced with the given value.
*/
- (void)setValue:(nullable NSString *)value forHTTPHeaderField:(NSString *)field;

/*! 
    @discussion This method provides a way to add values to header
    fields incrementally. If a value was previously set for the given
    header field, the given value is appended to the previously-existing
    value. 
*/
- (void)addValue:(NSString *)value forHTTPHeaderField:(NSString *)field;

2、setValue: forHTTPHeaderField会覆盖之前设置请求头，而addValue: forHTTPHeaderField并不会覆盖；由此可以通过覆盖的方式setValue:nil forHTTPHeaderField:xxx来删除xxx请求头：

[request setValue:nil forHTTPHeaderField:@"xxx"];