protected void ddlSubCht_SelectedIndexChanged(object sender, EventArgs e) 
         { 
             for (int i = 0; i  < gvCategories.Rows.Count; i++) 
             { 
                 DropDownList ddl = (DropDownList)gvCategories.Rows[i].FindControl("ddlSubCht");//问题1:在Debug下发现不能找到控件 
                 int ddlint = Convert.ToInt32(ddl.SelectedValue);//问题2:提示"未将对象引用设置到对象的实例" 
                 int key = (int)gvCategories.DataKeys[i].Value;//问题3:总是返回的同一个值.我想返回的是每行对应的DataKeys 
  
                 lbl.Text= ddlint+"_"+key+"_"+isSingle.ToString();//输出 
             } 
         } 
 

protected void ddlSubCht_SelectedIndexChanged(object sender, EventArgs e)
{
   DropDownList ddl = (DropDownList)sender;
   int ddlint = Convert.ToInt32(ddl.SelectedValue);
   int key = (int)gvCategories.DataKeys[(ddl.Parent as GridViewRow).RowIndex].Value;
   ..
}

------解决方案--------------------
C# code

foreach (GridViewRow row in this.GvCaseApplyList.Rows)
{
CheckBox chkPunish = (CheckBox)row.FindControl("chkCaseApply");
id=this.GvCaseApplyList.DataKeys[row.RowIndex][1].ToString();
}

------解决方案--------------------
 DropDownList ddl = (DropDownList)gvCategories.Rows[i].FindControl("ddlSubCht");//问题1:在Debug下发现不能找到控件
  定位不对吧....你这对应的是第几行...单元格呢?

------解决方案--------------------
DropDownList ddl = gvCategories.Rows[i].FindControl("ddlSubCht") as DropDownList;//

另外还要精确到cell

------解决方案--------------------
探讨

C# code
protected void ddlSubCht_SelectedIndexChanged(object sender, EventArgs e)
{
   DropDownList ddl = (DropDownList)sender;
   int ddlint = Convert.ToInt32(ddl.SelectedValue);
   int key = (int)gvCategories.DataKeys[(ddl.Parent as GridViewRow).RowIndex].Value;
   ..
}


------解决方案--------------------

DropDownList ddl = (DropDownList)gvCategories.Rows[i].FindControl("ddlSubCht");
测试了一下,可以找到控件啊,你看看是不是数据什么的出错了.

------解决方案--------------------