Handling an openFileDialog in the View of my MVP WinForms project
In the big if you have the following:


Path.GetExtension(openFileDialog1.FileName) == ".txt" || Path.GetExtension(openFileDialog1.FileName) == ".csv")



Why? You already put openFileDialog1.FileName in a fileName variable. Just use that.

The next thing I would do is define a list of valid extensions:

public readonly string[] ValidExtensions =&gt; new string[] { "txt", "csv" }


Then simply:

if (result == DialogResult.OK &amp;&amp; ValidExtensions.Contains(Path.GetExtension(fileName).Substring(1)))


We use the .Substring(1) to remove the period.

That way, if you add support for a different file type, you just add it to ValidExtensions.