DataGrid事件无法响应——初探

这段时间做的一些基于web的项目里面经常会用到DataGrid，有些复杂的功能是在代码中动态生成DataGrid来实现，比如一些自己开发的web control、user control里。

DataGrid确实很好用，但有时会出一些奇怪的问题，比如ItemCommand、PageIndexChanged不响应等，显得很诡异（页面会postback，就是不响应事件）。比如下面这个测试的user control，就一个简单的分页功能，第1页怎么都不响应：

namespace S3WebTest
...{
using System;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
//using Microsoft.SharePoint;
//using Microsoft.SharePoint.WebControls;
using System.Collections;
using System.IO;

/**//// <summary>
/// Summary description for TestGrid.
/// </summary>
public class TestGrid : System.Web.UI.UserControl
...{
protected System.Web.UI.WebControls.PlaceHolder phMain;

private Hashtable _htGrids = new Hashtable();
DataGrid MyGrid=new DataGrid();

private void Page_Load(object sender, System.EventArgs e)
...{
// Put user code to initialize the page here
}

Web Form Designer generated code#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
...{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
CreateDataGrids();
ShowDataGrids();

//RegScripts();

base.OnInit(e);
}

/**//// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
...{
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion

private void dg_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
...{
DataGrid dg = (DataGrid) source;
dg.CurrentPageIndex = e.NewPageIndex;
dg.DataBind();
}

private DataSet dsSource = new DataSet();


private void ShowDataGrids()
...{
DataTable dt = new DataTable();
dt.Columns.Add("id");
dsSource.Tables.Add(dt);
for (int j=0;j<12;j++)
...{
DataRow dr = dt.NewRow();
dr["id"] = j.ToString();
dt.Rows.Add(dr);
}

phMain.Controls.Clear();

MyGrid.AutoGenerateColumns = false;
MyGrid.AllowPaging = true;
MyGrid.PageSize = 2;
MyGrid.PagerStyle.Mode = PagerMode.NumericPages;
MyGrid.ItemCommand
MyGrid.PageIndexChanged +=new DataGridPageChangedEventHandler(dg_PageIndexChanged);
MyGrid.DataSource = dsSource;
MyGrid.DataBind();

phMain.Controls.Add(MyGrid);

}

private void CreateDataGrids()
...{
BoundColumn bc=new BoundColumn();
bc.HeaderText="id";
bc.DataField = "id";
MyGrid.Columns.Add(bc);
}

}
}

调试了一上午后发现，假如页面是postback的话DataGrid的DataBind操作放在事件代码前执行的话肯定就会出问题（哪位大虾能告诉我这是为什么？？），所以必须要把DataBind放在!IsPostBack里面，然后再到事件响应代码里执行DataBind，修改后的代码如下：

namespace S3WebTest
...{
using System;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
//using Microsoft.SharePoint;
//using Microsoft.SharePoint.WebControls;
using System.Collections;
using System.IO;

/**//// <summary>
/// Summary description for TestGrid.
/// </summary>
public class TestGrid : System.Web.UI.UserControl
...{
protected System.Web.UI.WebControls.PlaceHolder phMain;

private Hashtable _htGrids = new Hashtable();
DataGrid MyGrid=new DataGrid();

private void Page_Load(object sender, System.EventArgs e)
...{
// Put user code to initialize the page here
if (!this.Page.IsPostBack)
...{
MyGrid.DataBind();
}
}

Web Form Designer generated code#region Web Form Designer generated code
override protected void OnInit(EventArgs e)
...{
//
// CODEGEN: This call is required by the ASP.NET Web Form Designer.
//
InitializeComponent();
CreateDataGrids();
ShowDataGrids();

//RegScripts();

base.OnInit(e);
}

/**//// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
...{
this.Load += new System.EventHandler(this.Page_Load);
}
#endregion

private void dg_PageIndexChanged(object source, DataGridPageChangedEventArgs e)
...{
DataGrid dg = (DataGrid) source;
dg.CurrentPageIndex = e.NewPageIndex;
dg.DataBind();
}

private DataSet dsSource = new DataSet();


private void ShowDataGrids()
...{
DataTable dt = new DataTable();
dt.Columns.Add("id");
dsSource.Tables.Add(dt);
for (int j=0;j<12;j++)
...{
DataRow dr = dt.NewRow();
dr["id"] = j.ToString();
dt.Rows.Add(dr);
}

phMain.Controls.Clear();

MyGrid.AutoGenerateColumns = false;
MyGrid.AllowPaging = true;
MyGrid.PageSize = 2;
MyGrid.PagerStyle.Mode = PagerMode.NumericPages;
MyGrid.ItemCommand
MyGrid.PageIndexChanged +=new DataGridPageChangedEventHandler(dg_PageIndexChanged);
MyGrid.DataSource = dsSource;
//MyGrid.DataBind();

phMain.Controls.Add(MyGrid);

}

private void CreateDataGrids()
...{
BoundColumn bc=new BoundColumn();
bc.HeaderText="id";
bc.DataField = "id";
MyGrid.Columns.Add(bc);
}

}
}

这样就能正常响应事件了。