未选择文件时如何显示错误答案

【问题标题】：How to display error when no file selected未选择文件时如何显示错误
【发布时间】：2012-09-05 17:31:06
【问题描述】：

我们的经典 ASP 应用程序使用一个 .aspx 页面为每个客户端上传图像。我不熟悉 ASP.net，所以这个页面对我来说很难理解。

<html>
<head>
    <link href="css/style.css" rel="stylesheet" type="text/css" />
    <script language="VB" RunAt="Server">

        Sub Page_Load(Sender As Object, e As EventArgs)
            Span1.InnerHtml = "You may not upload a file larger than 250 Kilobytes. Your image must be in JPG format.<br />Please crop your image to 400 pixels high and 300 pixels wide, so that no distortion will occur when displayed.<br /><br />"
        End Sub

        Sub Upload_Click(Sender As Object, e As EventArgs)
            Dim DistributorID As Integer
            DistributorID = request.QueryString("distID")

            ' Display properties of the uploaded file

            'Let us recover only the file name from its fully qualified path at client 

            Dim strFileName As String
            strFileName = MyFile.PostedFile.FileName
            Dim c As String = CStr(DistributorID) & "." & split(System.IO.Path.GetFileName(strFileName), ".")(1) ' The file name is the distid + the extension

            'Let us Save uploaded file to server 
            If LCase(Split(System.IO.Path.GetFileName(strFileName), ".")(0)) = "" Then
                Span1.InnerHtml = "Please select a Photo.<br /><br />"
            End If

            If LCase(Split(System.IO.Path.GetFileName(strFileName), ".")(1)) <> "jpg" Then
                Span1.InnerHtml = "Invalid file format."
            Else

                If MyFile.PostedFile.ContentLength < 250000 Then
                    MyFile.PostedFile.SaveAs(ConfigurationSettings.AppSettings("DistImagePath") + c)
                    Span1.InnerHtml = "Your file imported sucessfully to the server.<br /><br />"
                Else
                    Span1.InnerHtml = "Your file is too large to import.<br /><br />"
                End If
            End If

        End Sub

    </script>
</head>
<body>      
    <span id="Span1" style="color:Red;" RunAt="Server" />                   
    <form method="Post" enctype="Multipart/Form-Data" RunAt="Server" class="stdform stdform2">
        &nbsp;&nbsp;Select New Photo: <br />
        &nbsp;<input id="MyFile" type="File" runat="Server" size="40" /><br /><br />            
        <span style="padding-left:25px;">
            <button type="Submit" value="Import" OnServerclick="Upload_Click" RunAt="Server">Upload New Photo</button>
        </span>
    </form>
</body>

如果没有选择文件并且按下上传新照片按钮，我会得到一个 “指数数组的边界之外。”错误

如果他们没有选择照片，我如何修复此页面以不尝试上传照片？

【问题讨论】：

标签： asp.net image error-handling

【解决方案1】：

您可以将所有内容都包含在 IF 中：

IF MyFile.PostedFile.ContentLength>0 Then 'User selected a file

   'All your code here
Else
    Span1.InnerHtml = "Your did not select a file.<br /><br />"
End IF

完整代码：

 Sub Upload_Click(Sender As Object, e As EventArgs)
    IF MyFile.PostedFile.ContentLength>0  Then   
        Dim DistributorID As Integer
        DistributorID = request.QueryString("distID")

        ' Display properties of the uploaded file

        'Let us recover only the file name from its fully qualified path at client 

        Dim strFileName As String
        strFileName = MyFile.PostedFile.FileName
        Dim c As String = CStr(DistributorID) & "." & split(System.IO.Path.GetFileName(strFileName), ".")(1) ' The file name is the distid + the extension

        'Let us Save uploaded file to server 
        If LCase(Split(System.IO.Path.GetFileName(strFileName), ".")(0)) = "" Then
            Span1.InnerHtml = "Please select a Photo.<br /><br />"
        End If

        If LCase(Split(System.IO.Path.GetFileName(strFileName), ".")(1)) <> "jpg" Then
            Span1.InnerHtml = "Invalid file format."
        Else

            If MyFile.PostedFile.ContentLength < 250000 Then
                MyFile.PostedFile.SaveAs(ConfigurationSettings.AppSettings("DistImagePath") + c)
                Span1.InnerHtml = "Your file imported sucessfully to the server.<br /><br />"
            Else
                Span1.InnerHtml = "Your file is too large to import.<br /><br />"
            End If
        End If
     Else
            Span1.InnerHtml = "Your did not select a file.<br /><br />"
     End IF

    End Sub

【讨论】：

那么您是否建议将 IF 语句放在 Upload_Click Sub 周围？

【解决方案2】：

If MyFile.PostedFile.ContentLength>0 
  ..
Else
   Span1.InnerHtml = "You have not specified a file."
End If

您可以在执行之前添加此代码（如果您要执行上传文件）

If FileUpload1.HasFile Then

    ......

Else
      Span1.InnerHtml = "You have not specified a file."
End If

【讨论】：

不，他没有使用常规的 ASP.NET 文件上传控件...查看标记