asp.net 2.0中判断上传的图片是否符合规格

在asp.net 2.0中，在上传图片时，有时往往要判断用户上传的图片是否符合指定规格，如果不符合规格，
则不予以上传，那么可以用以下的代码片段进行判断。
首先在web.config文件中设置图片上传的限制尺寸，比如
<appSettings>
<add key="RequiredHeight" value="184"/>
<add key="RequiredWidth" value="370"/>
</appSettings>

之后，在页面获得web.config文件里预先设定的尺寸

if (Page.IsPostBack)
{
height = Convert.ToInt32(
ConfigurationManager.AppSettings.Get("RequiredHeight"));
width = Convert.ToInt32(
ConfigurationManager.AppSettings.Get("RequiredWidth"));
}

之后在“上传”按钮的事件代码中如下编写

if (Page.IsValid)
{
if (FileUpload1.HasFile)
{
string extension = Path.GetExtension(FileUpload1.PostedFile.FileName);
switch (extension.ToLower())
{
case ".gif":
case "jpg":
try
{
//如果符合尺寸
if (ValidateFileDimensions())
{
string fileName = Path.GetFileName(FileUpload1.PostedFile.FileName);
string saveAsName = Path.Combine(Server.MapPath("~/Uploads/"), fileName);
FileUpload1.PostedFile.SaveAs(saveAsName);
lblSucces.Visible = true;
}
else
{
valInvalidDimensions.IsValid = false;
valInvalidDimensions.ErrorMessage = String.Format(valInvalidDimensions.ErrorMessage, height, width);
}
}
catch
{
// Unable to read the file dimensions. The uploaded file is probably not an image.
valInvalidFile.IsValid = false;
}
break;

default: // The uploaded file has an incorrect extension
valInvalidFile.IsValid = false;
break;
}
}
}

public bool ValidateFileDimensions()
{
using (System.Drawing.Image myImage = System.Drawing.Image.FromStream(FileUpload1.PostedFile.InputStream))
{
return (myImage.Height == height && myImage.Width == width);
}
}

要留意其中ValidateFileDimensions()中完成了判断尺寸的过程了
最后，页面放一些验证控件
<form id="form1" runat="server">
<div>
<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="btnUpload" runat="server" OnClick="btnUpload_Click" Text="Upload File" />
<br />
<asp:RequiredFieldValidator ID="valFileUpload1" ControlToValidate="FileUpload1" ErrorMessage="You must select a file first." runat="server" Display="Dynamic" />
<asp:CustomValidator ID="valInvalidFile" runat="server" ErrorMessage="The file you uploaded doesn't appear to be a valid image." Display="Dynamic"></asp:CustomValidator>
<asp:CustomValidator ID="valInvalidDimensions" runat="server" ErrorMessage="The image you uploaded has incorrect dimensions. Please select a file with a height of {0}px and a width of {1}px." Display="Dynamic" EnableViewState="false"></asp:CustomValidator>
<asp:Label ID="lblSucces" runat="server" Text="The file you uploaded has been saved to disk successfully." Visible="false" EnableViewState="false"></asp:Label>
</div>
</form>