SQL 服务器删除数据库失败

我有一个SQL Server数据库和该数据库的旧备份。有时我必须使用 C# WinForms 应用程序验证备份副本中的某些数据。我使用这篇文章还原备份文件： 如何还原到 sql 服务器中的其他数据库？.

我的恢复功能如下所示：

SqlConnection myConn = new SqlConnection("Server=.''sqlexpress;Database=master;Trusted_Connection=True;");
try
{
    if (!Databases.CheckDatabaseExists(myConn, fileName))
    {
        myConn.Open();
        SqlCommand cmd = new SqlCommand("RESTORE FILELISTONLY FROM DISK='" + fileName + ".bak'", myConn);
        SqlDataReader reader = cmd.ExecuteReader();
        cmd.CommandText = "restore database " + Path.GetFileName(fileName) + " from disk = '" + fileName + ".bak' with move'";
        int i = 0;
        while (reader.Read())
        {
            if (i == 0)
            {
                cmd.CommandText += reader[0].ToString() + "' to '" + filePath + "''" + Path.GetFileName(fileName) + ".mdf', move ";
                i++;
            }
            else
            {
                cmd.CommandText += "'" + reader[0].ToString() + "' to '" + filePath + "''" + Path.GetFileName(fileName) + ".mdf.ldf'";
            }
        }
        reader.Close();
        cmd.ExecuteNonQuery();
        myConn.Close();
        database.ReadDataBaseIstoric(dataGridView1, Path.GetFileName(fileName));
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
    finally
    {
        if (myConn.State == ConnectionState.Open) { myConn.Close(); }
    }

和

database.ReadDataBaseIstoric(dataGridview1,Path.GetFileName(filename)); 

从还原的数据库中读取数据，如下所示：

public void ReadDataBaseIstoric(DataGridView dataGridView1, string dataBaseName)
    {
        dataGridView1.Rows.Clear();
        SqlConnection conn = new SqlConnection("Server=.''sqlexpress;Trusted_Connection=true;database=" + dataBaseName + ";");
        SqlDataReader reader = null;
        try
        {
            conn.Open();
            SqlCommand  cmd = new SqlCommand("select * from istoric", conn);
            conn.Close();
            reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                string[] str = new string[5] { reader[0].ToString(), reader[1].ToString(), reader[2].ToString(), reader[3].ToString(), reader[4].ToString() };
                dataGridView1.Rows.Add(str);
            }
            reader.Close();
            conn.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            if (reader != null && !reader.IsClosed) { reader.Close(); }
            if (conn.State == ConnectionState.Open) { conn.Close(); }
        }
    }

目前一切正常。问题是，当我尝试删除还原的数据库时，它会返回 en 错误，指出无法删除该数据库，因为它仍在使用中。这就是我想删除数据库的方式：

private void Arhiva_FormClosing(object sender, FormClosingEventArgs e)
{
        bool closed = false;
        if (!closing) { e.Cancel = true; closing = false; closed = true; }
        SqlConnection myConn = new SqlConnection("Server=.''sqlexpress;Database=master;Trusted_Connection=True;");
        try
        {
            if (Databases.CheckDatabaseExists(myConn, Path.GetFileName(fileName)))
            {
                myConn.Open();
                SqlCommand cmd = new SqlCommand("DROP DATABASE "+Path.GetFileName(fileName), myConn);
                cmd.ExecuteNonQuery();
                myConn.Close();
                label1.Visible = false;
            }
            else
            {
                MessageBox.Show("Exista deja o baza de date cu numele '" + fileName + "'.", "VivaFEED", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
        finally
        {
            if (myConn.State == ConnectionState.Open) { myConn.Close(); }
        }
        if (closed) { this.Close(); }
  }

我尝试在从中读取数据之前删除还原的数据库，并且效果很好，所以我认为问题应该出在database.ReadDataBaseIstoric()上。

附言我也使用 database.ReadDataBaseIstoric() 函数从当前数据库（不是还原的备份）中读取数据，它在那里工作得很好，没有任何错误或异常。

public void ReadDataBaseIstoric(DataGridView dataGridView1, string dataBaseName)
{
    dataGridView1.Rows.Clear();
    using(SqlConnection conn = new SqlConnection("Server=.''sqlexpress;Trusted_Connection=true;database=" + dataBaseName + ";"))
    using(SqlCommand  cmd = new SqlCommand("select * from istoric", conn))
    {
        SqlDataReader reader = null;
        try
        {
            conn.Open();
            using(SqlDataReader reader = cmd.ExecuteReader())
            {
                while (reader.Read())
                {
                    string[] str = new string[5] { reader[0].ToString(), reader[1].ToString(), reader[2].ToString(), reader[3].ToString(), reader[4].ToString() };
                    dataGridView1.Rows.Add(str);
                }
            }
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message);
        }
    }
}