code: @Override
      public void onBackPressed() {
      	// Verify if the activity must be finished or if the parent folder must be opened.
     	    File current = this.core.getCurrentFolder();
     	    if(!this.useBackButton || current == null || current.getParent() == null || current.getPath().compareTo(this.startFolder.getPath()) == 0) {
     	    	// Close activity.
     	    	super.onBackPressed();
     	    }else{
     	    	// Open parent.
     	        this.core.loadFolder(current.getParent());
     	    }
    	}
docs: Called when the user push the 'back' button.