用DataGrid展示目录下的文件 (第二部分)


在第一部分,我们创建了一个DataGrid控件以显示某个目录下的文件,在本节,我们看如何扩展示例,允许用户仅仅点击一个按钮来删除某个文件。

  为DataGrid控件添加Delete按钮

  假设我们优化前面的那个示例(示例页面为:http://aspnet.4guysfromrolla.com/demos/ListArticles.aspx),允许用户删除目录下的某个文件.为此,我们可以在DataGrid控件里添加一个名为"Delete" 的ButtonColumn ,添加后,DataGrid控件的声明代码开起来应该和下面的差不多:

<form runat="server">
 <asp:DataGrid runat="server" id="articleList" Font-Name="Verdana"
   AutoGenerateColumns="False" AlternatingItemStyle-BackColor="#eeeeee"
   HeaderStyle-BackColor="Navy" HeaderStyle-ForeColor="White"
   HeaderStyle-Font-Size="15pt" HeaderStyle-Font-Bold="True"
  <Columns>
   <asp:ButtonColumn Text="Delete" ButtonType="PushButton"
         CommandName="Delete" />
   <asp:HyperLinkColumn DataNavigateUrlField="Name" DataTextField="Name"
         HeaderText="File Name" />
   <asp:BoundColumn DataField="LastWriteTime" HeaderText="Last Write Time"
    ItemStyle-HorizontalAlign="Center" DataFormatString="{0:d}" />
   <asp:BoundColumn DataField="Length" HeaderText="File Size"
  ItemStyle-HorizontalAlign="Right"
  DataFormatString="{0:#,### bytes}" />
  </Columns>
 </asp:DataGrid>
</form>

仔细查看上面的代码示例,我们注意到如下3方面:

  1.为DataGrid添加了一个ButtonColumn,显示为一个"Delete"按钮.

  2.该ButtonColumn的CommandName属性被设置为Delete,那意味着当点击该按钮时触发DataGrid控件的DeleteCommand事件.

  3.该DataGrid被放置在Web form里(the <form runat="server">...</form>),这是必要的,因为DataGrid现在包含一个ButtonColumn.

  现在我们将为DataGrid的DeleteCommand事件创建一个事件处理器。当DataGrid的某个行记录的 "Delete" 按钮点击时,就触发该事件处理器。所以该处理器先要确定待删除文件的路径,再将其删除掉。

  为了确定用户将要删除的文件,我们把DataGrid的DataKeyField属性设置为FileInfo class类的FullName属性.这就意味着,我们可以确定待删除文件的完整路径.代码如下:

<form runat="server">
 <asp:DataGrid runat="server" id="articleList"
   ...
   DataKeyField="FullName">
  <Columns>
   ...
  </Columns>
 </asp:DataGrid>
</form>

  剩下要做的便是为DataGrid的DeleteCommand事件创建一个事件处理器.在该处理器里我们需要确定要删除的文件,再通过File.Delete()方法将其删掉.最终的示例代码如下.除了删除文件以外,示例代码还包含一个客户端确认对话框,当用户点击"Delete"按钮后,提醒用户是否真的要删除文件.(关于这种客户端事件的更多讨论见文章《 An Extensive Examination of the DataGrid Web Control: Part 8! 》)
<%@ Import Namespace="System.IO" %>
<script language="VB" runat="server">
 Sub Page_Load(sender as Object, e as EventArgs)
  If Not Page.IsPostBack then
   Dim dirInfo as New DirectoryInfo(Server.MapPath(""))
  
   articleList.DataSource = dirInfo.GetFiles("*.aspx")
   articleList.DataBind()
  End If
 End Sub
 
 Sub articleList_ItemDataBound(sender as Object, e as DataGridItemEventArgs)
  ' First, make sure we're NOT dealing with a Header or Footer row
  If e.Item.ItemType <> ListItemType.Header AND _
     e.Item.ItemType <> ListItemType.Footer then
   'Now, reference the Button control that the Delete ButtonColumn
   'has been rendered to
   Dim deleteButton as Button = e.Item.Cells(0).Controls(0)
  
   'We can now add the onclick event handler
   deleteButton.Attributes("onclick") = "javascript:return " & _
         "confirm('Are you sure you want to delete the file " & _
         DataBinder.Eval(e.Item.DataItem, "Name") & "?')"  
  End If
 End Sub
 
 
 Sub articleList_DeleteFile(sender as Object, e as DataGridCommandEventArgs)
  'First, get the filename to delete
  Dim fileName as String = articleList.DataKeys(e.Item.ItemIndex)
  
  lblMessage.Text = "You opted to delete the file " & _
    fileName & ".<br />" & _
    "This file could be deleted by calling: " & _
    "<code>File.Delete(fileName)</code><p>"
  
  'You would want to rebind the Directory's files to the DataGrid after
  'deleting the file...
 End Sub
</script>
  
<form runat="server">
 <asp:label runat="server" id="lblMessage" Font-Italic="True" ForeColor="Red" />
 <asp:DataGrid runat="server" id="articleList" Font-Name="Verdana"
   AutoGenerateColumns="False" AlternatingItemStyle-BackColor="#eeeeee"
   HeaderStyle-BackColor="Navy" HeaderStyle-ForeColor="White"
   HeaderStyle-Font-Size="15pt" HeaderStyle-Font-Bold="True"
   DataKeyField="FullName"
   OnItemDataBound="articleList_ItemDataBound"
   OnDeleteCommand="articleList_DeleteFile">
  <Columns>
   <asp:ButtonColumn Text="Delete" ButtonType="PushButton"
       CommandName="Delete" />
   <asp:HyperLinkColumn DataNavigateUrlField="Name"
       DataTextField="Name" HeaderText="File Name" />
   <asp:BoundColumn DataField="LastWriteTime"
       HeaderText="Last Write Time"
       ItemStyle-HorizontalAlign="Center"
       DataFormatString="{0:d}" />
   <asp:BoundColumn DataField="Length" HeaderText="File Size"
      ItemStyle-HorizontalAlign="Right"
      DataFormatString="{0:#,### bytes}" />
  </Columns>
 </asp:DataGrid>
</form>
  结语:

  本文我们考察了如何使用NET Framework的与文件系统相关的类,以及如何用DataGrid控件展示指定目录下的文件.另外,我们考察了如何优化DataGrid包含一列"Delete" 按钮,供用户删除某个文件.只需要最少的代码和最短的程序调试时间便可达到上述目的.

  祝编程快乐!


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