Gridview小技巧保存選擇狀態

gridview 缺省的分頁是一次性載入所有數據,對大一點的項目肯定是不行的,所以大家都會用其它的分頁控件一頁一頁載入數據.

做批量操作時通常會有一個"CheckBox"列,但如果翻頁就需要保存選擇的狀態,用viewstate來保存還是比較簡單的.

下面代碼放到分頁改變事件中用來把選擇ID列表保存到viewstate中.

    
    protected void AspNetPager1_PageChanged(object sender, EventArgs e)
    {

        #region save select status

        List<string> IDList = new List<string>();

        if (ViewState["IDList"] != null)
            IDList = (List<string>)ViewState["IDList"];

        int i = 0;

        for (i = 0; i < gvData.Rows.Count; i++)
        {
            string ID = gvData.DataKeys[i].Value.ToString();

            if (((CheckBox)gvData.Rows[i].FindControl("select")).Checked)
            {                
                if (!IDList.Contains(ID))
                    IDList.Add(ID);
            }
            else
            {
                if (IDList.Contains(ID))
                    IDList.Remove(ID);

            }
        }

        ViewState["IDList"] = IDList;

        #endregion

        //做分頁的其他事情.
    }

下面的代碼,gridview在邦定數據時根據viewstate決定是否選擇.

        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            #region get the select status and decide the checbox select status

            List<string> IDList = new List<string>();
            if (ViewState["IDList"]!=null)
                IDList = (List<string>)ViewState["IDList"];

            string ID = gvData.DataKeys[e.Row.RowIndex].Value.ToString();

            CheckBox cb = (CheckBox)e.Row.Cells[0].FindControl("select");
            if (IDList.Contains(ID))
            {
                cb.Checked = true;
            }
            else
            {
                cb.Checked = false;
            }

            #endregion

        }

    //使用的時候也一樣,從viewstate中讀出ID列表
            List<string> IDList = new List<string>();
            if (ViewState["IDList"]!=null)
                IDList = (List<string>)ViewState["IDList"];