数据筛选和排序

  一.TreeView

   SelectedNode 选中的节点
   Level 节点的深度（从0开始） 
   AfterSelect 节点选中后发生

   1.获取节点深度

    this.tvlist.SelectNode.Level

   2.获取节点名称

    this.tvlist.SelectNode.Text

  二.使用DataView筛选和排序数据

   RowFilter指定筛选条件
   Sort指定排序方式

   //窗体运行时默认选中全部
            if (this.tvstulist.SelectedNode.Level == 0) {
                ShowStudent();
            }
            else if (this.tvstulist.SelectedNode.Level == 1) {
                DataView dv = new DataView(ds.Tables["Student"]);
                dv.RowFilter = "GradeName='"+this.tvstulist.SelectedNode.Text+"'";
                this.dgvstulist.DataSource = dv;
            }
            else if (this.tvstulist.SelectedNode.Level == 2) {
               
                DataView dv = new DataView(ds.Tables["Student"]);
                dv.RowFilter = "GradeName='" + this.tvstulist.SelectedNode.Parent.Text + "' and Sex='" + this.tvstulist.SelectedNode.Text + "'";
                dv.Sort = "StudentNo desc";
                this.dgvstulist.DataSource=dv;
            }

        三.删除数据

         SelectionMode指定选中DataGradeView的选中方式

         DialogResult result= MessageBox.Show("是否删除","提示",MessageBoxButtons.YesNo,MessageBoxIcon.Information);
            if (result == DialogResult.Yes) {
                //获取选中的学号的值
                int studentno=(int)this.dgvstulist.SelectedRows[0].Cells["StudentNo"].Value;
                try
                {
                    helper.OpenConnection();
                    string sql = "delete from Student where StudentNo='"+studentno+"'";
                    SqlCommand cmd = new SqlCommand(sql,helper.Con);
                    int count=cmd.ExecuteNonQuery();
                    if (count > 0)
                    {
                        MessageBox.Show("删除成功！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                        ShowStudent();
                    }
                    else {
                        MessageBox.Show("删除失败！", "提示", MessageBoxButtons.OK, MessageBoxIcon.Information);
                    }
                }
                catch (Exception x)
                {
                    MessageBox.Show(x.Message);
                }
            }