How can i resolve path in c#

Hello ,i have a function which combine path.
Example

My application is located in D:\toto\titi\tata\myapplication.exe

And I create a windows form application(c#) which solve the relative path  based on the path of my application (D:\toto\titi\tata\myapplication.exe).

I want to this this :


1)Path to resolve is  test.txt  => D:\toto\titi\tata\test.txt

2)Path to resolve is  .\..\..\test\test.txt  => D:\toto\test\test.txt

3)Path to resolve is  .\..\test\test.txt  => D:\toto\titi\test\test.txt

4)Path to resolve is  .\..\..\..\test\test.txt  => D:\test\test.txt

5)Path to resolve is  .\..\..\..\..\test\test.txt  => The path doesn't exist

6)Path to resolve is  \\server\share\folder\test => get the corresponding path in the server.



I use this method


private void btnSearchFile_Click(object sender, EventArgs e)
        {
            // Open an existing file, or create a new one.
            FileInfo fi = new FileInfo(@"D:\toto\titi\tata\myapplication.exe");


            // Determine the full path of the file just created or opening.
            string fpath = fi.DirectoryName;


            // First case.
            string relPath1 = txtBoxSearchFile.Text;
            FileInfo fiCase1 = new FileInfo(Path.Combine(fi.DirectoryName, relPath1.TrimStart('\\')));


            //Full path
            string fullpathCase1 = fiCase1.FullName;


            txtBoxFoundFile.Text = fullpathCase1;
        }






but i doesn't solve point 1);point 5) and point 6)

Can you help me