如何在文件名上传到asp.net之前检查文件名答案

【问题标题】：How to check filename before its upload in asp.net如何在文件名上传到asp.net之前检查文件名
【发布时间】：2020-02-04 01:51:51
【问题描述】：

我打算做的是当我点击上传按钮时，系统会检查选择的文件名是否与我想要的文件名相同（在文件上传之前）。

string selectedValue = version.SelectedItem.Value;
string serverPath;

if (FileUpload1.PostedFile.FileName != "")
{
    if (selectedValue == "1")
    {
        // check extension of file before uploading
        if (FileUpload1.PostedFile.FileName == "MyApp.apk")
        {
            serverPath = "C:/MyPath/MyApp.apk";
            FileUpload1.PostedFile.SaveAs(serverPath);
            ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('file has been uploaded successfully');window.location.href = '" + Request.RawUrl + "'; ", true);
        }
        else if (FileUpload1.PostedFile.FileName == "MyApp.ipa")
        {
            serverPath = "C:/MyPath/MyApp.ipa";
            FileUpload1.PostedFile.SaveAs(serverPath);
            ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('file has been uploaded successfully');window.location.href = '" + Request.RawUrl + "'; ", true);
        }
        else
        {
            ClientScript.RegisterStartupScript(this.GetType(), "myalert", "alert('Please select MyApp file to upload');window.location.href = '" + Request.RawUrl + "'; ", true);
        }
    }
}

但我得到的是，系统会先上传文件并显示我设置的警报消息。

如何在默认上传栏出现之前先显示错误消息（选择了错误的文件）？

【问题讨论】：

comapre 字符串。 if (FileUpload1.PostedFile.FileName.Equals(selectedFileName)) { // proceed with upload }

标签： c# asp.net file-upload

【解决方案1】：

如果您需要在提交页面之前进行检查，您可以使用客户端 onchange 事件输入 type=file，如下所示：

    <html>
        <body>
            <form>
                <div>
                    file: <input type="file" id="fileupload" />
                </div>
            </form>
            <script>
                document.getElementById('fileupload').addEventListener('change', onUpload);
                function onUpload(e){
                    var files = this.files;
                    if ( files && files.length==1 
                        &&  ( files[0].name.toLowerCase() === "myapp.apk" || files[0].name.toLowerCase() === "myapp.ipa"  )
                        )
                    {
                        //allow to submit file
                    }
                    else{
                        //cancel form submission
                        this.value = "";
                        alert('Please select MyApp file to upload');
                    }
                }
            </script>
        </body>
    </html>

【讨论】：

但我想知道如何强制用户再次选择或删除选定的文件？