To use a StreamReader you need to construct it passing, at least, the filename to read.
This could be accomplished using the OpenFileDialog variable declared at the form global level
// Show the OpenFileDialog and wait for user to close with OK
if(filechooser.ShowDialog() == DialogResult.OK)
{
// Check if the file exists before trying to open it
if(File.Exists(filechooser.FileName))
{
// Enclose the streamreader in a using block to ensure proper closing and disposing
// of the file resource....
using(StreamReader fileReader = new StreamReader(filechooser.FileName))
{
string inputrecord = fileReader.ReadLine();
string[] inputfields;
....
// The remainder of your code seems to be correct, but a check on the actual
// length of the array resulting from the Split call should be added for safety
}
}
}
Notice that both the OpenFileDialog and the StreamReader are complex objects that have many properties and different ways to work. You really need to look at their constructors and properties list in the MSDN documentation to exploit their full functionality