使用gridview在rowdatabound事件上的下拉列表中獲取空值

Question

我收到錯誤消息：- "Object reference not set to an instance of an object."

當我想將數據綁定到dropdownlist這會給我錯誤。 這是我的代碼：

protected void EventRequirementGridView_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
         DropDownList ddllist = (DropDownList)e.Row.FindControl("modeldropdownlist");

         ddllist.SelectedValue = DataBinder.Eval(e.Row.DataItem, "exammode").ToString();               
    }
}

Answer 1

這樣嘗試

protected void EventRequirementGridView_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow && && e.Row.RowState == DataControlRowState.Edit)
    {                     
           DropDownList ddllist = (DropDownList)e.Row.FindControl("modeldropdownlist");
           ddllist.SelectedValue = DataBinder.Eval(e.Row.DataItem, "exammode").ToString();               
    }
}

（要么）

 protected void EventRequirementGridView_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow && && e.Row.RowState == DataControlRowState.Edit)
        {
           if ((e.Row.RowState & DataControlRowState.Edit) > 0)
            {            
               DropDownList ddllist = (DropDownList)e.Row.FindControl("modeldropdownlist");
               ddllist.SelectedValue = DataBinder.Eval(e.Row.DataItem, "exammode").ToString();               
            }
         }
    }

另外，您可以使用GridView的PreRender事件從EditItemTemplate訪問控件，例如：

protected void GridView1_PreRender(object sender, EventArgs e) 
{
  if (GridView1.EditIndex != -1) 
  {
     //Just changed the index of cells based on your requirements
     DropDownList ddllist = (DropDownList)e.Row.FindControl("modeldropdownlist");
     ddllist.SelectedValue = DataBinder.Eval(e.Row.DataItem, "exammode").ToString();              
  }
}