show a file chooser dialog

src/main.vala

@@ -12,7 +12,17 @@ int main(string[] args)
 
     var button = new Button.with_label("Select a file");
     button.clicked.connect(() => {
-        button.label = "clicked";
+        var file_chooser = new FileChooserDialog(
+            "Open File",
+            null,
+            FileChooserAction.OPEN,
+            Stock.CANCEL, ResponseType.CANCEL,
+            Stock.OPEN, ResponseType.ACCEPT);
+        if (file_chooser.run() == ResponseType.ACCEPT)
+        {
+            stdout.printf("File selected: %s\n", file_chooser.get_filename());
+        }
+        file_chooser.destroy();
     });
 
     window.add(button);