设置 NSMutableURLRequest header 和添加一个之间的区别
Difference between setting an NSMutableURLRequest header and adding one
我想知道设置 header 值和向 NSMutableURLRequest 添加 header 值之间的区别是什么。听起来很明显，但是，例如，您不能每次都使用 addValue 吗？设置不存在的 header 会抛出错误吗？如果 header 已存在于请求中，添加它是否会覆盖现有值？
例子
let request.NSMutableURLRequest(URL: NSURL(string: "someURL")!)
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
...
我觉得苹果官方文档的讨论很清楚：
This method provides the ability to add values to header fields incrementally. If a value was previously set for the specified field, the supplied value is appended to the existing value using the appropriate field delimiter. In the case of HTTP, the delimiter is a comma.
The new value for the header field. Any existing value for the field
is replaced by the new value.
setValue 替换。 addValue 附加分隔符
我想知道设置 header 值和向 NSMutableURLRequest 添加 header 值之间的区别是什么。听起来很明显，但是，例如，您不能每次都使用 addValue 吗？设置不存在的 header 会抛出错误吗？如果 header 已存在于请求中，添加它是否会覆盖现有值？
例子
let request.NSMutableURLRequest(URL: NSURL(string: "someURL")!)
request.addValue("application/json", forHTTPHeaderField: "Content-Type")
...
我觉得苹果官方文档的讨论很清楚：
This method provides the ability to add values to header fields incrementally. If a value was previously set for the specified field, the supplied value is appended to the existing value using the appropriate field delimiter. In the case of HTTP, the delimiter is a comma.
The new value for the header field. Any existing value for the field is replaced by the new value.
setValue 替换。 addValue 附加分隔符