请问老师 在上传图片前 怎么判断是否有图片才能上传？

Select Case e.Path
    Case "upload.htm"
        Dim wb As New weui
        wb.AddForm("","form1","receive.htm")
        With wb.AddInputGroup("form1","ipg1","文件上传")
            With .AddUploader("up128","照片",True)
                .AllowDelete = True \'允许删除
                .Incremental = True \'允许重复选择文件或连续拍照
                .ScaleWidth = 400 \'自动压缩图片宽度为400个像素,高度等比例压缩
            End With
        End With
        With wb.AddButtonGroup("form1","btg1",True)
            .Add("btn1", "确定", "button").Attribute= "" \'调用js函数上传
        End With
        wb.AddToast("","tst1", "正在上传",1)
        wb.AddToast("","tst2", "上传成功",0)
        wb.AddToast("","tst3", "上传失败",0).Icon= "warn"
        wb.AppendHTML("<script src=\'./lib/ajaxform.js\'></script>") \'引入脚本文件
        e.WriteString(wb.Build) \'生成网页
    Case "receive.htm"
        For Each key As String In e.Files.Keys
            For Each fln As String In e.Files(key)
                e.SaveFile(key,fln,"d:\\web\\uploadfiles\\" & fln) \'保存接收到的文件
            Next
        Next
        e.WriteString("OK")
End Select