Getting the local file path of selected file

I browse the file system to select a file. It gives me the file name. I need the complete file location on device to give as input to my function. This code works well when the parameter passed to the UplaodFunction is hard coded path. When trying to pass dynamically, it throws an exception

AzureViacSharp1.CSharpClass  testingDll;

           InteropPermission p;

           str fileUrl;

           FileUploadTemporaryStorageResult result = File::GetFileFromUser() as FileUploadTemporaryStorageResult;

           if (result && result.getUploadStatus())

           {

               fileUrl = result.getDownloadUrl();

               info(fileUrl);

           }

           p = new InteropPermission(InteropKind::DllInterop);

           p.assert();

           testingDLL = new AzureViacSharp1.CSharpClass();

           System.IO.Path::Combine();

           testingDll.UploadFunction(@'fileUrl');

           info(strFmt("Success"));