HttpResponse does not contain a definition for AddHeader for Dot Net Core

Question

When moving a project into .Net Core, AddHeader throws an error:

Error CS1061 \'HttpResponse\' does not contain a definition for \'Add

Answer 1

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Examples:

string combineValue = httpContext.Request.Headers["header1];
if (string.IsNullOrEmpty(combineValue)) // ...
var values = httpContext.Request.Headers["header1"];
if (StringValues.IsNullOrEmpty(values)) // ...
httpContext.Response.Headers["CustomHeader1"] = "singleValue";
httpContext.Response.Headers["CustomHeader2"] =  new[] { "firstValue", "secondValue" };