对 gridview 控件进行排序 - 方向永远不会改变

Question

即使看了几个例子，我似乎也无法理解这一点。

我有这段代码，它很高兴按升序重新排序我的网格视图：

    // gridViewSorting and ConvertSortDirectionToSql are both necessary to ensure the gridview can sort when their column headers are
    //   clicked.  You must remember to add (AllowSorting="True" OnSorting="gridViewSorting") to the gridview tag on the ASP side
    protected void gridViewSorting(object sender, GridViewSortEventArgs e)
    {
       DataTable dataTable = GVInactive.DataSource as DataTable;

       if (dataTable != null)
       {
          DataView dataView = new DataView(dataTable);
          string SQL = "[" + e.SortExpression + "] " + ConvertSortDirectionToSql(e.SortDirection);
          dataView.Sort = SQL;

          GVInactive.DataSource = dataView.ToTable();
          GVInactive.DataBind();

       }
    }

    private string ConvertSortDirectionToSql(SortDirection sortDirection)
    {
        string newSortDirection = String.Empty;

        switch (sortDirection)
        {
            case SortDirection.Ascending:
                newSortDirection = "DESC";
                break;

            case SortDirection.Descending:
                newSortDirection = "ASC";
                break;
        }

        return newSortDirection;
    }

但是，我第二次单击标题时，它应该颠倒以前的排序顺序。它永远不会。每次我单击列的标题时，它都会点击case SortDirection.Ascending: 行并设置newSortDirection = "DESC"。数据按降序排序，但是当我再次单击标题时，它将 SortDirection 解析为升序。

有什么想法吗？

Answer 1

我们使用 ViewState 变量来存储最新的排序方向。当网格被排序时，我们将网格的排序标准和排序方向与存储最后排序表达式的 ViewState 变量进行比较。如果列相等，则检查先前排序的方向并按相反方向排序。

例子：

    private string SortCriteria
    {
        get
        {
            if (ViewState["sortCriteria"] == null)
            {
                ViewState["sortCriteria"] = "";
            }

            return ViewState["sortCriteria"].ToString();
        }
        set
        {
            ViewState["sortCriteria"] = value;
        }
    }

    private string SortDirection
    {
        get
        {
            if (ViewState["sortDirection"] == null)
            {
                ViewState["sortDirection"] = "";
            }

            return ViewState["sortDirection"].ToString();
        }
        set
        {
            ViewState["sortDirection"] = value;
        }
    }

    protected void gvData_Sorting(object sender, GridViewSortEventArgs e)
    {
        gvData.EditIndex = -1;

        if (SortCriteria == e.SortExpression)
        {
            if (SortDirection == string.Empty || SortDirection == "DESC") { SortDirection = "ASC"; }
            else { SortDirection = "DESC"; }
        }
        else
        {
            SortCriteria = e.SortExpression;
            SortDirection = "ASC";
        }

        BindGrid();
    }

    private void BindGrid()
    {
        DataTable dt = new [However you get dataset from database];
        DataView dv = new DataView(dt);
        dv.Sort = string.Format("{0} {1}", SortCriteria, SortDirection).Trim();

        gvData.DataSource = dv;
        gvData.DataBind();
    }

Answer 2

为了记录，我用这个替换了我的问题中使用的代码，它完美地工作：

    // gridViewSorting and ConvertSortDirectionToSql are both necessary to ensure the gridview can sort when their column headers are
    //   clicked.  You must remember to add (AllowSorting="True" OnSorting="gridViewSorting") to the gridview tag on the ASP side
    protected void gridViewSorting(object sender, GridViewSortEventArgs e)
    {
        DataTable dataTable = GVInactive.DataSource as DataTable;
        string sortExpression = e.SortExpression; 
        string direction = string.Empty;

        if (dataTable != null)
        {
            DataView dataView = new DataView(dataTable);

            if (SortDirection == SortDirection.Ascending) 
            { 
                SortDirection = SortDirection.Descending; 
                direction = " DESC"; 
            } 
            else 
            { 
                SortDirection = SortDirection.Ascending; 
                direction = " ASC"; 
            }

            DataTable table = GVInactive.DataSource as DataTable;
            table.DefaultView.Sort = sortExpression + direction;

            GVInactive.DataSource = table;
            GVInactive.DataBind();

        }
    }

    public SortDirection SortDirection 
    { 
        get 
        { 
            if (ViewState["SortDirection"] == null) 
            { 
                ViewState["SortDirection"] = SortDirection.Ascending; 
            } 
            return (SortDirection)ViewState["SortDirection"]; 
        } 
        set 
        { 
            ViewState["SortDirection"] = value; 
        } 
    }

我可能可以删除几行（不确定我什至是否需要 DataView），但它可以正常工作。只记得在 GridView 标记中将这些片段添加到 ASP 端：

AllowSorting="True" OnSorting="gridViewSorting"

然后在适当的地方更改您的网格视图的名称。