How to make main window wait until a newly opened window closes in C# WPF?

I am new to WPF as well as C#, please bear with me.

I have a main window which opens up a new window. Now this new window is a prompt whether or not to overwrite a file, and the main window accesses a public variable in the new window to check for the prompt's result.

But I can't get the main window processing to wait until the new window closes.

 Window1 Win = new Window1();
 Win.Show();

 if (Win.pr_res == 1)
 {
      abc.Text = "File to be overwritten";
      File.Delete(_destination);
      Start();
 }
 else
 {
      abc.Text = "Operation Aborted";
 }

I tried adding a while loop checking another public boolean in the main window, but that just hangs the entire program.

 while(!_closecheck);

Any suggestions are welcome.