无法从“ System.Drawing.Bitmap”转换为与“ SMTP”附件相关的“字符串”

如何解决无法从“ System.Drawing.Bitmap”转换为与“ SMTP”附件相关的“字符串”

下面的功能负责获取面板的屏幕截图并将其用作电子邮件的附件，而无需将其存储在本地计算机中。

我设法做到了，但是有一个小问题，它给了我这个错误：

无法从“ System.Drawing.Bitmap”转换为“字符串”

我知道也有类似的问题，但是我不知道该如何解决。

private void btnSend_Click(object sender,EventArgs e)
{
    //using (var bmp = new Bitmap(workPanel.Width,workPanel.Height))
    //{
    //  workPanel.DrawToBitmap(bmp,new Rectangle(0,bmp.Width,bmp.Height));
    //  bmp.Save(@"images/" + name.Text + ".png");
    //}
    try
    {
        using (var bmp = new Bitmap(workPanel.Width,workPanel.Height))
        {
            MailMessage mail = new MailMessage();
            SmtpClient smtp = new SmtpClient("smtp.gmail.com");
            mail.From = new MailAddress("[e-mail]");
            mail.To.Add(txtTo.Text); // Receivers email address comes here
            mail.Subject = txtTitle.Text;
            mail.Body = txtBody.Text;
            mail.IsBodyHtml = true; // TO HAVE THE BODY AS HTML

            System.Net.Mail.Attachment attachment;
            //attachment = new System.Net.Mail.Attachment(lblLocation.Text);
            attachment = new System.Net.Mail.Attachment(bmp); // <-------- ERROR COMES HERE
            mail.Attachments.Add(attachment);

            smtp.Port = 587;
            smtp.Credentials = new System.Net.NetworkCredential("[e-mail]","password");
            smtp.EnableSsl = true;
            smtp.Send(mail);
            MessageBox.Show("Mail has been sent");
        }
    }
    catch(Exception ex)
    {
        //MessageBox.Show(ex.Message);
        MessageBox.Show("Something went wrong,this might be a problem from our end.\n" + ex.Message,"Please contact support team");
    }
}

解决方法

发生错误的原因很简单：类Attachment没有使用BitMap的构造函数。

幸运的是，有一个构造器需要一个Stream。 Bit，BitMap没有方法将其转换为Stream。幸运的是，BitMap实现了ISerializable，因此我们可以将BitMap保存在流中，然后使用Attachment（Stream，...）构造函数

让我们使用make Extension方法将BitMap转换为Stream，并将Stream转换为Attachment。参见extension methods demystified

static System.IO.Stream ToStream(this System.Drawing.BitMap bmp)
{
    // TODO: exception if bmp null
    var stream = new MemoryStream();
    Bitmap.Save(ms,Bitmap.RawFormat);
    return stream;
}
static System.Net.Mail.Attachment ToAttachment(this System.Drawing.BitMap bmp)
{
    // TODO: bmp is null

    const string contentType = "image/jpg";
    return new System.Net.Mail.Attachment(bmp.ToStream(),contentType);
}

用法：

BitMap bmp = ...
Attcahment attachement = bmp.ToAttachment();