OpenFileDialog openFileDialog = new OpenFileDialog();
openFileDialog.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*";
int[] a = new int[10];
if (openFileDialog.ShowDialog() == DialogResult.OK)
{
   obj.SetText(File.ReadAllText(openFileDialog.FileName));
}

int[] a = textBox1.Text.Split(' ').Select(x => int.Parse(x)).ToArray();

int[] a = textBox1.Text.Split(' ').
          Where(x => !string.IsNullOrWhiteSpace( x )).
          Select(x => int.Parse(x)).ToArray();

int[] result = textBox1.Text.Split( new[]{" "}, StringSplitOptions.RemoveEmptyEntries ).Select(x => int.Parse(x)).ToArray();

text.Split(new[]{' '},StringSplitOptions.RemoveEmptyEntries).Select(int.Parse).ToArray();