how to use file.close()

Hey, I'm having some trouble creating a file to store data, I'm using

StreamWriter file;

void start() {

file = new StreamWriter("file.txt"); }

void update(){

file.WriteLine("data bla bla bla");

if (Input.GetKeyDown ("space")) {

         file.Close ();
         print ("end");
     }

}

I don't understand why it is not working, I've already have used this same code in the past, so it doesn't make sense why it's not working, it doesn't write anything in the file, and also it doesn't detect when I press the spacebar

Any ideas?