DataGrid双向排序以及给HeaderText加图标

DataGrid双向排序以及给HeaderText加图标

DataGrid默认情况下只支持单向排序，而且默认是升序（ASC）。能不能使之支持双向排序并且给HeaderText加图标呢？
       下面的例子将演示如何给DataGrid动态添加sortexpression 和 sortdirection 属性，并通过DataView使DataGird中的数据按照这两个属性排列。
        假设在页面上添加了一个ID=“showdata”的DataGrid。使用Northwind数据库中的customers表来说明这个例子。
       首先，我们必须知道：
        (1).数据源一定是Dataview,因为DataView提供了一种过滤和排序DataTable中数据的一种方式。
        (2).DataGrid的AllowSorting属性要为True。
        (3).DataGrid的AutogenerateColumns属性要为False
        (4).添加要绑定的字段到DataGrid，并设置Sortexpression属性和数据库中数据表中的字段名保持一致。

   //在页面第一次被加载时给DataGrid添加动态属性sortexpression 和 sortdirection，
   //给指定的字段的sortexpression 和 sortdirection 赋值，在加载时初始化DataGrid的排序字段和排序方式
    protected void Page_Load(object sender, System.EventArgs e)
    {
        if (!IsPostBack)
        {
            if (showdata.Attributes["SortExpression"] == null)
            {
                showdata.Attributes["SortExpression"] = "CustomerID";
                showdata.Attributes["SortDirection"] = "ASC";
            }
            BindGrid();
        }
    }

    //  得到DataSet 和 DataView 对象。设置DataView 的sort 属性为动态属性sortexpression 和 sortdirection的连接字符串
    private void BindGrid()
    {
        SqlConnection conn = new SqlConnection("server=localhost;uid=sa;pwd=sa;database=Northwind");
        conn.Open();
        SqlDataAdapter cmd = new SqlDataAdapter("select * from customers", conn);
        DataSet ds = new DataSet();
        cmd.Fill(ds, "customers");
        DataView dv = new DataView(ds);
        string SortExpression = showdata.Attributes["SortExpression"];
        string SortDirection = showdata.Attributes["SortDirection"];
        dv.Sort = SortExpression + " " + SortDirection;
        this.showdata.DataSource = dv;
        this.showdata.DataBind();
    }

   //不要图标的SortCommand事件
    private void showdata_SortCommand(object source, System.Web.UI.WebControls.DataGridSortCommandEventArgs e)
    {

        string SortExpression = e.SortExpression.ToString();
        string SortDirection = "ASC";
        if (SortExpression == showdata.Attributes["SortExpression"])
        {
            SortDirection = (showdata.Attributes["SortDirection"].ToString() == SortDirection ? "DESC" : "ASC");
        }
        showdata.Attributes["SortExpression"] = SortExpression;
        showdata.Attributes["SortDirection"] = SortDirection;
        BindGrid();
    }

    //要图标的SortCommand事件，当表头被点击时，触发DataGrid的sortcommand事件，得到sortcommand事件传递过来的sortexpression属性，并与datagrid的sortexpression属性比较，再比较SortDirection……
    protected void showdata_SortCommand(object source, DataGridSortCommandEventArgs e)
    {
        string ImgDown = "<img border=0 src=" + Request.ApplicationPath + "/uparrow.gif>";
        string ImgUp = "<img border=0 src=" + Request.ApplicationPath + "/downarrow.gif>";
        string SortExpression = e.SortExpression.ToString();
        string SortDirection = "ASC";
        int colindex = -1;
        //清空之前的图标
        for (int i = 0; i < showdata.Columns.Count; i++)
        {
            showdata.Columns[i].HeaderText = (showdata.Columns[i].HeaderText).ToString().Replace(ImgDown, "");
            showdata.Columns[i].HeaderText = (showdata.Columns[i].HeaderText).ToString().Replace(ImgUp, "");
        }
        //找到所点击的HeaderText的索引号
        for (int i = 0; i < showdata.Columns.Count; i++)
        {
            if (showdata.Columns[i].SortExpression == e.SortExpression)
            {
                colindex = i;
                break;
            }
        }
        if (SortExpression == showdata.Attributes["SortExpression"])
        {

            SortDirection = (showdata.Attributes["SortDirection"].ToString() == SortDirection ? "DESC" : "ASC");

        }
        showdata.Attributes["SortExpression"] = SortExpression;
        showdata.Attributes["SortDirection"] = SortDirection;
        if (showdata.Attributes["SortDirection"] == "ASC")
        {
            showdata.Columns[colindex].HeaderText = showdata.Columns[colindex].HeaderText + ImgDown;
        }
        else
        {
            showdata.Columns[colindex].HeaderText = showdata.Columns[colindex].HeaderText + ImgUp;
        }
        BindGrid();
    }