private void button1_Click(object sender, EventArgs e)
        {
            FormLaporanPembelian frm = new FormLaporanPembelian();

            frm.Owner = this;
            frm.Show();
        }
        private void laporanBulanToolStripMenuItem_Click(object sender, EventArgs e)
        {
            //FormLaporanPembelian beli = new FormLaporanPembelian();
            //beli.ShowDialog();

            //buka form laporan pembelian
            Form form = Application.OpenForms["FormLaporanPembelian"];

            if (form == null)                                                     //jika form ini belum pernah di-create sebelumnya
            {
                FormLaporanPembelian frmLpPembelian = new FormLaporanPembelian(); //create objek formdaftarkategori
                frmLpPembelian.MdiParent = this;                                  //set form utama menjadi parent dari objek form yang dibuat
                frmLpPembelian.Show();                                            //tampilkan form
            }
            else
            {
                form.Show();
                form.BringToFront();//agar form tampil di paling depan
            }
        }