B4X

Set a MIME Header Field

Demonstrates the Chilkat Mime.SetHeaderField method, which sets a single header field. The first argument is the field name and the second is the value. All existing occurrences are removed and one replacement is inserted, or a new field is added if none exists.

Background: For headers that should appear exactly once — Subject, From, Content-Type — this is the method to use, because it guarantees a single occurrence no matter how many times you call it. That idempotence is the key difference from AddHeaderField, which would leave duplicates behind. Setting an empty value removes the field.

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Dim success As Boolean = False

'  Demonstrates the Mime.SetHeaderField method, which sets a single header field.  The 1st argument
'  is the field name and the 2nd is the value.  All existing occurrences are removed and one
'  replacement is inserted (or a new field is added if none exists).

Dim mime As ChilkatMime
mime.Initialize

success = mime.SetBodyFromPlainText("Hello.")
If success = False Then
    Log(mime.LastErrorText)
    Return
End If


'  Unlike AddHeaderField, SetHeaderField ensures exactly one field with this name.
success = mime.SetHeaderField("Subject", "Weekly Report")
If success = False Then
    Log(mime.LastErrorText)
    Return
End If


'  Setting it again replaces the previous value rather than adding a duplicate.
success = mime.SetHeaderField("Subject", "Weekly Report (revised)")
If success = False Then
    Log(mime.LastErrorText)
    Return
End If


Dim subject As String = mime.GetHeaderField("Subject")
If mime.LastMethodSuccess = False Then
    Log(mime.LastErrorText)
    Return
End If

Log("Subject: " & subject)