检查 pdf 标志 pdfAnnotation.HasFlag 错误时出现问题

Question

我正在开发一个检查 PDF 注释的工具。我能够检查标志，但在一个特定标志上出现错误。可能是什么原因？

    Public Sub GetComments()

    Dim oComments As New PDFcomments
    Dim reader As PdfReader = New PdfReader("C:\Users\jeee\Desktop_3047 - Type 1.pdf")
    Dim pdfdocument As New PdfDocument(reader)


    For i As Integer = 1 To pdfdocument.GetNumberOfPages

        Dim pdfPage As PdfPage = pdfdocument.GetPage(i)
        Dim oAnnotations As IList(Of Annot.PdfAnnotation) = pdfPage.GetAnnotations()


        For Each oAnnotation As Annot.PdfAnnotation In oAnnotations

            Dim oAnnotationSubType As PdfName = oAnnotation.GetSubtype

            If oAnnotationSubType.ToString = "/FreeText" Then
                Debug.Print(oAnnotation.GetTitle.ToString)
                Debug.Print(oAnnotation.GetContents.ToString)
                Debug.Print(oAnnotation.GetFlags)

                Debug.Print(oAnnotation.HasFlag(1))
                Debug.Print(oAnnotation.HasFlag(2))
                Debug.Print(oAnnotation.HasFlag(3))
                Debug.Print(oAnnotation.HasFlag(4))

            End If

        Next
    Next

End Sub

System.ArgumentException: 'Only one flag must be checked at once.'

导致错误的行：Debug.Print(oAnnotation.HasFlag(3))

调试结果。

JeEe Test annotation 4 False False

注意：如果我将行 Debug.Print(oAnnotation.HasFlag(4)) 放在 Debug.Print(oAnnotation.HasFlag(3)) 前面，错误仍然发生在同一行。

Answer 1

HasFlag记录如下：

    /// <summary>
    /// Checks if the certain flag that specifies a characteristic of the annotation
    /// is in enabled state (see ISO-320001 12.5.3, "Annotation Flags").
    /// </summary>
    /// <remarks>
    /// Checks if the certain flag that specifies a characteristic of the annotation
    /// is in enabled state (see ISO-320001 12.5.3, "Annotation Flags").
    /// This method allows only one flag to be checked at once, use constants listed in
    /// <see cref="SetFlag(int)"/>
    /// .
    /// </remarks>
    /// <param name="flag">
    /// an integer interpreted as set of one-bit flags. Only one bit must be set in this integer, otherwise
    /// exception is thrown.
    /// </param>
    /// <returns>true if the given flag is in enabled state.</returns>
    public virtual bool HasFlag(int flag)

因此，参数必须是 一个整数，解释为一组一位标志。此整数中只能设置一位。 整数 3 显然设置了两位。

您似乎认为该参数的意思类似于第 n 个标志，但它实际上意味着 具有值 n 的标志。

所以允许的值为 1、2、4、8，...但尤其不能是 3。

检查 pdf 标志 pdfAnnotation.HasFlag 错误时出现问题

Problem checking pdf flags pdfAnnotation.HasFlag error

flags

annotations

itext

itext7