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近期碰到一个查询页面，逻辑很简单，就是查询资料并显示．但用户较多，提出的修改需求较频繁，有几个同事先后修改过．　开始新建时，查询用了sql + sqlparameter得到结果显示；后来用户增加查询条件, 另一同事用了Row filter进行过滤，再后来用户又加查询条件，又有同事用了 Linq过滤, 　hahahaha． 现在用户又要加查询条件．　打开代码一看，晕服了，各个方法间关联度很大，耦合度高，动一毛牵全身，要同时修改几个方法的内容，下决心还是重写．

主要思路：从Database get数据后，利用委托事件对数据进行过滤操作．

部分代码：

public delegate void QueryDelegate();//声明一个委托    public partial class SearchClientCode : Form    {
                  DataTable clientDt;//这个是查询结果的初始表　按过滤条件进行筛选后的最新结果        DataTable clientDtInit = new DataTable(); //这个等于查询结果的初始表clientDt，作为过滤条件重置后的重新查询用．　当然，条件重置后也可以采取重新从DATABASE获取的方式．        Form parent;        public QueryDelegate querydelegate; //也可以用 public Action queryAction;               public SearchClientCode(Form parent)        {
               InitializeComponent();                  }        //page_load        private void SearchClientCode_Load(object sender, EventArgs e)        {
               //get Client Datatable            clientDt = getClientDt();            clientDtInit = clientDt.Copy(); //注意，要用copy,,copy to a init datatable for query reset            // add RetSetQueryTb to delegate 			//以下是各种过滤条件，加入到委托．            querydelegate += RetSetClientDt;　            querydelegate += Filter_ClientName;            querydelegate += Filter_Status;            querydelegate += Filter_ModifyDate;            querydelegate();//进行过滤                 bindDgv();　//显示查询结果        }                    //bind datagridview        private void bindDgv()        {
               dgvClient.DataSource = clientDt.DefaultView;            hlper.customDataGuidView(dgvClient, getClientMapping());            dgvClient.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;        }        //Reset the query to init        private void RetSetClientDt()        {
               clientDt = clientDtInit.Copy();        }        #region condition changed events.        private void btnCurr_Click(object sender, EventArgs e)        {
               string firstdayofmonth = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).ToString("dd-MM-yyyy");            string lastdayofmonth = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).AddMonths(1).AddDays(-1).ToString("dd-MM-yyyy");            dtpDateFr.Text = firstdayofmonth;            dtpDateTo.Text = lastdayofmonth;            ModifyDate_Changed();        }       ....        //search  client name text changed        private void txtSearch_TextChanged(object sender, EventArgs e)        {
                           dgvClient.DataSource = clientDt.AsEnumerable().Where((o) => o.Field
   
    ("Client_Name").ToUpper().Contains(txtSearch.Text.Trim().ToUpper())).AsDataView();            hlper.customDataGuidView(dgvClient, getClientMapping());            dgvClient.AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.AllCells;        }        //Modify_date changed        private void ModifyDate_Changed()        {
               if (!querydelegate.GetInvocationList().AsEnumerable().Contains((QueryDelegate)Filter_ModifyDate))            {
                   querydelegate += Filter_ModifyDate;            }            querydelegate();            bindDgv();        }               //RadioButton - Frozen All changed        private void rbBlAll_CheckedChanged(object sender, EventArgs e)        {
               if ((sender as RadioButton).Checked) // if selected            {
                   querydelegate -= Filter_FrozenStatus;            }            querydelegate();            bindDgv();        }        //RadioButton - Frozen Status Frozen/Release changed        private void rbBlFrozen_CheckedChanged(object sender, EventArgs e)        {
               if ((sender as RadioButton).Checked)            {
                   if (querydelegate.GetInvocationList().AsEnumerable().Contains((QueryDelegate)Filter_FrozenStatus))                {
                       querydelegate -= Filter_FrozenStatus;                }                querydelegate += Filter_FrozenStatus;//get the lastest filter delegate                querydelegate();                bindDgv();            }        }       //重点：如果有新增的过滤条件　，参考上面的事件增加一个新事件．（就是往委托中增加／更新／删除过滤事件）	   ．．．．．．        #endregion        #region filter delegate actions        //filter client name        private void Filter_ClientName()        {
               if (!string.IsNullOrEmpty(txtSearch.Text.Trim()))            {
                   clientDt = clientDt.AsEnumerable().Where((o) => o.Field
    
     ("Client_Name").ToUpper().Contains(txtSearch.Text.Trim().ToUpper())).AsDataView().ToTable();            }        }        //filter modify date        private void Filter_ModifyDate()        {
               clientDt = clientDt.AsEnumerable().Where((o) => o.Field
     
      ("modify_date") >= DateTime.Parse(dtpDateFr.Text) && o.Field
      
       ("modify_date") <= DateTime.Parse(dtpDateTo.Text + " 23:59:59")).AsDataView().ToTable();        }               //filter BL        private void Filter_FrozenStatus()        {
               string frozenstatus = rbBlFrozen.Checked ? "Frozen" : rbBlRel.Checked ? "Release" : "";            clientDt = clientDt.AsEnumerable().Where((o) => Convert.ToString(o["BLStatus"]) == frozenstatus).AsDataView().ToTable();        }        //filter quot status        private void Filter_QuotStatus()        {
               string quotstatus = rbQuotStatusStop.Checked ? "Stop" : rbQuotStatusRel.Checked ? "Release" : "";            clientDt = clientDt.AsEnumerable().Where((o) => Convert.ToString(o["QuotStatus"]) == quotstatus).AsDataView().ToTable();        }		//重点：如果有新增的过滤条件　，参考上面的方法增加一个新方法．(利用Linq进行条件过滤)		//......        #endregion    }
      
     
    
   

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