Question

我正在尝试确保用户不下载将替换现有下载（相同）文件的文件。因此，我尝试创建YesNo对话框供用户确认。但是，即使该文件夹中没有“sample.xml”，当用户单击“下载”按钮时，仍会显示“YesNo”对话框。我可以知道我在哪里做错了吗？我缺乏编程知识，抱歉，请耐心等待。

我的代码如下：

private void btnDownloadXML2_Click(object sender, EventArgs e)
{
    if (@"..\..\sharePriceXML\" + txtSharePriceSymbol.Text.ToString() + ".xml" != null)
    {
        DialogResult dialogResult = MessageBox.Show("Are you sure you want to re-download the file? This will replace the old file!", "Warning", MessageBoxButtons.YesNo);
        if (dialogResult == DialogResult.Yes)
        {
            using (WebClient client = new WebClient())
            {
                client.DownloadFile("http://www.lse.co.uk/chat/" + txtSharePriceSymbol.Text.ToString(),
                                    @"..\..\sharePriceXML\" + txtSharePriceSymbol.Text.ToString() + ".xml");
            }
            MessageBox.Show("Download Completed! File has been placed in the folder sharePriceXML!");
        }
        else if (dialogResult == DialogResult.No)
        {
            MessageBox.Show("The file is not downloaded. Your old file remains.");
        }
    }
    else if (@"..\..\sharePriceXML\" + txtSharePriceSymbol.Text.ToString() + ".xml" == null)
    {
        using (WebClient client = new WebClient())
        {
            client.DownloadFile("http://www.lse.co.uk/chat/" + txtSharePriceSymbol.Text.ToString(),
                                @"..\..\sharePriceXML\" + txtSharePriceSymbol.Text.ToString() + ".xml");
        }
        MessageBox.Show("Download Completed! File has been placed in the folder sharePriceXML!");
    }
}

Answer 1

您正在将文件路径检查为字符串以查看它是否为空...它永远不会为空，因为它具有文件路径。

您需要使用File.Exists()。而不是：

if (@"..\..\sharePriceXML\" + txtSharePriceSymbol.Text.ToString() + ".xml" != null)

使用此：

if (File.Exists(@"..\..\sharePriceXML\" + txtSharePriceSymbol.Text.ToString() + ".xml"))

即使没有重复的文件，也会出现YesNo对话框

1 个答案: