知道我的打印对话框出现两次的原因吗？

Question

当我点击button1时，它会打开一个打印对话框但是当我关闭它时会打开另一个对话框。任何想法（根据我的代码）为什么？我确实检查了我的代码，但我没有看到任何冗余。谢谢另外，伙计们，在InitializeComponent

之后+ =表示什么

public partial class Print2 : Form
{
    public Print2()
    {
        InitializeComponent();
        this.button1.Click += button1_Click;
        this.printDocument1.PrintPage += printDocument1_PrintPage;
    }

    private void Print2_Load(object sender, EventArgs e)
    {
        this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
        this.WindowState = FormWindowState.Maximized;


        using (SqlConnection connection = new SqlConnection("Data Source=XXXX;Initial Catalog=XXXXX;Integrated Security=True"))
        {
            SqlCommand command =
            new SqlCommand("select [CustomerName],[Inserted] from baf where id=(select max(id) from baf)", connection);
            connection.Open();

            SqlDataReader read = command.ExecuteReader();

            while (read.Read())
            {
                textBox1.Text = (read["CustomerName"].ToString());
                textBox2.Text = (read["Inserted"].ToString());

            }
            read.Close();

        }
    }

    private void button2_Click(object sender, EventArgs e)
    {
        this.Close();
    }

    private void button1_Click(object sender, EventArgs e)
    {
        this.printPreviewDialog1.Document = this.printDocument1;
        this.printPreviewDialog1.Document.DocumentName = "PictureTextDesignerFile1";
        this.printPreviewDialog1.Size = new Size(1200, 800);
        this.printPreviewDialog1.ShowDialog();


    }



    private void printDocument1_PrintPage(object sender, System.Drawing.Printing.PrintPageEventArgs e)
    {

        float neededWidth = 840;

        float neededHeight = 1320;

        float availableWidth = 840;
        float availableHeight = 1320;

        e.Graphics.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
        e.Graphics.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAliasGridFit;
        e.Graphics.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.HighQualityBicubic;

        Bitmap bmpPrint = null;

        try
        {
            double multiplier = neededWidth / neededHeight;
            double dblRef = availableWidth / availableHeight;
            float zoom = 1;

            if (multiplier >= dblRef)
            {
                zoom = availableWidth / neededWidth;
            }
            else
            {
                zoom = availableHeight / neededHeight;
            }

            bmpPrint = new Bitmap(1200, 900);
            bmpPrint.SetResolution(300, 300);
            this.DrawToBitmap(bmpPrint, new Rectangle(0, 0, 2000, 2800));

            //this.DrawToBitmap(bmpPrint, new Rectangle(0, 0, bmpPrint.Width, bmpPrint.Height));

            e.Graphics.Clip = new Region(e.MarginBounds);
            e.Graphics.DrawImage(bmpPrint, e.MarginBounds.Left, e.MarginBounds.Top, Math.Min(neededWidth * zoom, availableWidth), Math.Min(neededHeight * zoom, availableHeight));
            e.Graphics.Clip.Dispose();
        }
        catch
        {
        }
        finally
        {
            if ((bmpPrint != null))
            {
                bmpPrint.Dispose();
                bmpPrint = null;
            }
        }







    }