How to set up spinner between SKScene transitions? - ios

Question

I have a very heavyweight scene that takes like 5 seconds to load.
I want some loading screen with a spinner to appear while it is waiting to load - what is elegant solution to that?
Should I make intermediate scene and show spinner on it while my scene loads?
Can I alloc and initWithSize scene in background thread?
Here is how I do it now:
MyScene *newScene = [[MyScene alloc] initWithSize:self.size];
SKTransition *transition = [SKTransition flipHorizontalWithDuration:1.0];
[self.view presentScene:newScene transition:transition];
But as soon as I press the button - game freezes for these 5 seconds and provides no feedback for player what is going on.
Tagging this as coco2d since it has very similar API and problems.

Answer 1

Don't do things like this on a background thread. What you can do is show your spinner first, then dispatch_async the actual transition:
// Write code for showing your spinner
dispatch_async(dispatch_get_main_queue(), ^{
MyScene *newScene = [[MyScene alloc] initWithSize:self.size];
SKTransition *transition = [SKTransition flipHorizontalWithDuration:1.0];
[self.view presentScene:newScene transition:transition];
});
This will show your spinner and on the next run loop execute the transition.

Answer 2

Here is my approach:
In Interface Builder add SKView, Loading image, Large White Activity Indicator to GameSceneViewController:
Add outlets for added controls to GameSceneViewController:
#interface GameSceneViewController : UIViewController
#property (nonatomic, weak) IBOutlet SKView *skView;
#property (weak, nonatomic) IBOutlet UIImageView *loadingScreen;
#property (weak, nonatomic) IBOutlet UIActivityIndicatorView *activityIndicator;
#end
In your SKScene add class method, which loads all assets for the scene:
+(void)loadSceneAssetsWithCompletionHandler:(AGAssetLoadCompletionHandler)handler {
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
// Load the shared assets in the background.
[self loadSceneAssets];
if (!handler) {
return;
}
dispatch_async(dispatch_get_main_queue(), ^{
// Call the completion handler back on the main queue.
handler();
});
});
}
where AGAssetLoadCompletionHandler is defined in GameScene.h as
/* Completion handler for callback after loading assets asynchronously. */
typedef void (^AGAssetLoadCompletionHandler)(void);
Same approach uses Apple in their Sprite Kit Adventure Game.
Finally, GameSceneViewController's viewWillAppear method:
- (void)viewWillAppear:(BOOL)animated
{
[super viewWillAppear:animated];
[self.activityIndicator startAnimating];
if (!self.skView.window) {
[self.view addSubview:self.skView];
}
[GameScene loadSceneAssetsWithCompletionHandler:^{
GameScene *scene = [[GameScene alloc] initWithSize:self.skView.bounds.size];
scene.scaleMode = SKSceneScaleModeAspectFit;
[self.skView presentScene:scene transition:[SKTransition crossFadeWithDuration:1]];
[self.activityIndicator stopAnimating];
[UIView animateWithDuration:1.0 delay:0.0 options:UIViewAnimationOptionCurveEaseInOut animations:^{
self.loadingScreen.alpha = 0.0f;
} completion:NULL];
}];
}