add SKAction to Sprite queue run one after another

Question

I listen to touch and add SKAction to a sprite. If existing actions are not complete yet, I want the action to be added to a queue so it will execute one after another. Any experienced similar design?

I did using Array and Block. If there is any easier approach?

@interface GAPMyScene()
@property(strong,nonatomic)SKSpriteNode*ufo;
@property(strong,nonatomic)NSMutableArray*animationQueue;
@property(copy,nonatomic)void(^completeMove)();
@end

@implementation GAPMyScene

-(id)initWithSize:(CGSize)size {
    if (self = [super initWithSize:size]) {
        self.ufo = [SKSpriteNode spriteNodeWithImageNamed:@"Spaceship"];
        self.animationQueue = [[NSMutableArray alloc] init];
        __unsafe_unretained typeof(self) weakSelf = self;
        self.completeMove = ^(void){
            [weakSelf.ufo runAction:[SKAction sequence:[weakSelf.animationQueue copy]] completion:weakSelf.completeMove];
            NSLog(@"removeing %@", weakSelf.animationQueue);
            [weakSelf.animationQueue removeAllObjects];
        };
        [self addChild:self.ufo];
    }
    return self;
}

-(void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{
    for (UITouch *touch in touches) {
        CGPoint location = [touch locationInNode:self];
        SKAction*moveAnimation = [SKAction moveTo:location duration:2];
        if (![self.ufo hasActions]) {
            [self.ufo runAction:moveAnimation completion:self.completeMove];

        } else {
            [self.animationQueue addObject:moveAnimation];
            NSLog(@"in queue %@", self.animationQueue);
        }
    }
}

@end

Answer 1

Generally, you can make SKActions run concurrently using the group method, and have them run sequentially using the sequence method.

But if you need a queuing system, rather than building your own, use the native operation queue to do this for you. So you can create a serial operation queue and add operations to it. The issue is that you don't want an operation to complete until the SKAction does.

So, you can wrap your SKAction in a concurrent NSOperation subclass that only completes when the SKAction does. Then you can add your operations to a serial NSOperationQueue, and then it will won't start the next one until it finishes the prior one.

So, first, create an ActionOperation (subclassed from NSOperation) that looks like:

// ActionOperation.h

#import <Foundation/Foundation.h>

@class SKNode;
@class SKAction;

@interface ActionOperation : NSOperation

- (instancetype)initWithNode:(SKNode *)node action:(SKAction *)action;

@end

and

// ActionOperation.m

#import "ActionOperation.h"
@import SpriteKit;

@interface ActionOperation ()

@property (nonatomic, readwrite, getter = isFinished)  BOOL finished;
@property (nonatomic, readwrite, getter = isExecuting) BOOL executing;

@property (nonatomic, strong) SKNode *node;
@property (nonatomic, strong) SKAction *action;

@end

@implementation ActionOperation

@synthesize finished  = _finished;
@synthesize executing = _executing;

- (instancetype)initWithNode:(SKNode *)node action:(SKAction *)action
{
    self = [super init];
    if (self) {
        _node = node;
        _action = action;
    }
    return self;
}

- (void)start
{
    if ([self isCancelled]) {
        self.finished = YES;
        return;
    }

    self.executing = YES;

    [[NSOperationQueue mainQueue] addOperationWithBlock:^{
        [self.node runAction:self.action completion:^{
            self.executing = NO;
            self.finished = YES;
        }];
    }];
}

#pragma mark - NSOperation methods

- (BOOL)isConcurrent
{
    return YES;
}

- (void)setExecuting:(BOOL)executing
{
    [self willChangeValueForKey:@"isExecuting"];
    _executing = executing;
    [self didChangeValueForKey:@"isExecuting"];
}

- (void)setFinished:(BOOL)finished
{
    [self willChangeValueForKey:@"isFinished"];
    _finished = finished;
    [self didChangeValueForKey:@"isFinished"];
}

@end

You could then, for example, create a serial queue during the initialization process:

self.queue = [[NSOperationQueue alloc] init];
self.queue.maxConcurrentOperationCount = 1;

You can then add the operations to it:

SKAction *move1 = [SKAction moveTo:point1 duration:2.0];
[self.queue addOperation:[[ActionOperation alloc] initWithNode:nodeToMove action:move1]];

and you can later add more actions:

SKAction *move2 = [SKAction moveTo:point2 duration:2.0];
[self.queue addOperation:[[ActionOperation alloc] initWithNode:nodeToMove action:move2]];

And because the queue is serial, you know that move2 will not be started until move1 is done.