C#连接SQL Server数据库的实例讲解

private void btn1_Click(object sender, EventArgs e)
    {
      if (txt1.Text == "")
      {
        MessageBox.Show("请输入要连接的数据库名称!");
      }
      else
      {
        try
        {
          string connString = "server=.;database=" + txt1.Text.Trim() + ";uid=test;pwd=test;connect timeout=5"; //**
          SqlConnection sqlConnection = new SqlConnection(connString); //**
          sqlConnection.Open(); //**

          if (sqlConnection.State == ConnectionState.Open)
          {
            lab2.Text = "数据库【" + txt1.Text.Trim() + "】已经连接并打开！";
          }
        }
        catch
        {
          MessageBox.Show("数据库连接失败!");
        }
      }
    }

SqlConnection sqlConnection; //***
    /// <summary>
    /// 连接数据库
    /// </summary>
    private void btn1_Click_1(object sender, EventArgs e)
    {
      if (txt1.Text == "")
      {
        MessageBox.Show("请输入数据库名称:");
      }
      else
      {
        try
        {
          string connString = "server=.;database=" + txt1.Text.Trim() + ";uid=test;pwd=test;connect timeout=5"; //***
          sqlConnection = new SqlConnection(connString); //***
          sqlConnection.Open(); //***

          if (sqlConnection.State == ConnectionState.Open)
          {
            btn1.Text = "连接成功";
          }
        }
        catch(Exception ex) 
        {
          MessageBox.Show(ex.Message);
          txt1.Text = "";
        }
      }
    }

    /// <summary>
    /// 使用Close方法关闭连接并重新调用Open方法连接数据库
    /// </summary>
    private void btn2_Click(object sender, EventArgs e)
    {
      try
      {
        string str = "";

        sqlConnection.Close(); //***
        if (sqlConnection.State == ConnectionState.Closed)
        {
          str = "数据库已经成功关闭\n";
        }

        sqlConnection.Open(); //***
        if (sqlConnection.State == ConnectionState.Open)
        {
          str += "数据库已经成功打开\n";
        }

        rtbox1.Text = str;
      }
      catch (Exception ex)
      {
        rtbox1.Text = ex.Message;
      }
    }

    /// <summary>
    /// 使用Dispose方法关闭连接并重新调用Open方法连接数据库
    /// </summary>
    private void btn3_Click(object sender, EventArgs e)
    {
      try
      {
        sqlConnection.Dispose(); //***
        sqlConnection.Open(); //***
      }
      catch (Exception ex)
      {
        rtbox1.Text = ex.Message;
      }
    }