Accessing an object's local variable from a method Objective-c

Question

I'm trying to access an object's local variable from didBeginContact method. How's it possible ?

Let's say I've got a ball object and whenever it bounces from the player, that ball's bouncedFrom variable get's an identifier from the player.

This is my initBall method, which initialises a ball. It is called every 3-5(random) seconds.

-(void)initBall {
NSString *bouncedFrom;
bouncedFrom = @"";

ball = [SKSpriteNode spriteNodeWithImageNamed:@"ball"];
ball.name = ballCategoryName;
ball.zPosition = 0;
int cannonPos = (arc4random() % 3 ) + 1;
SKSpriteNode *cannon = (SKSpriteNode *)[self childNodeWithName:[NSString stringWithFormat:@"%i",cannonPos]];
ball.zPosition = 3;
ball.position = cannon.position;
ball.physicsBody.categoryBitMask = ballCategory;
ball.physicsBody.contactTestBitMask = wallCategory;
ball.physicsBody.collisionBitMask = wallCategory;
ball.physicsBody.usesPreciseCollisionDetection = YES;
[self addChild:ball];

ball.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:ball.frame.size.width/2];
ball.physicsBody.friction = 0.0f;
//Bounce back
ball.physicsBody.restitution = 1.0f;
//
ball.physicsBody.linearDamping = 0.0f;
ball.physicsBody.allowsRotation = NO;
switch (cannonPos) {
    case 1:
        ball.position = CGPointMake(ball.position.x+20, ball.position.y+20);
        [ball.physicsBody applyImpulse:CGVectorMake(-1.0,1.0)];
        break;
    case 2:
        ball.position = CGPointMake(ball.position.x-20, ball.position.y+15);
        [ball.physicsBody applyImpulse:CGVectorMake(-1.0,1.0)];
        break;
    case 3:
        ball.position = CGPointMake(ball.position.x-20, ball.position.y-15);
        [ball.physicsBody applyImpulse:CGVectorMake(-1.0,-1.0)];
        break;
    case 4:
        ball.position = CGPointMake(ball.position.x+20, ball.position.y-20);
        [ball.physicsBody applyImpulse:CGVectorMake(-1.0,-1.0)];
    default:
        break;
}

What I want is something like this in the didBeginContact:

-(void)didBeginContact:(SKPhysicsContact *)contact {
SKPhysicsBody *firstBody;
SKPhysicsBody *secondBody;

if (contact.bodyA.categoryBitMask < contact.bodyB.categoryBitMask) {
    firstBody = contact.bodyA;
    secondBody = contact.bodyB;
} else {
    firstBody = contact.bodyB;
    secondBody = contact.bodyA;
}

if ((firstBody.categoryBitMask & ballCategory) !=0) {
    SKNode *ball = contact.bodyB.node;
    SKNode *player = contact.bodyA.node;

    ball.bouncedFrom = PlayerCategory;


}

if ((firstBody.categoryBitMask & wallCategory) !=0) {
    SKNode *ball = contact.bodyB.node;
    SKAction *addScore = [SKAction runBlock:^{
        if (ball.position.y < 0) playerScore--;
        if (ball.position.x < 0) cpu2Score--;
        if (ball.position.y > self.frame.size.height) cpu1Score--;
        if (ball.position.x > self.frame.size.width) cpu3Score--;
        }];
    SKAction *removeNode = [SKAction removeFromParent];
    SKAction *sequence = [SKAction sequence:@[addScore, removeNode]];
    [ball runAction:sequence];
}
}

Both ball and xCategories are declared as static variables at the top of my code. Is something like this possible ?

You have heard of ivars, yes? If not: http://stackoverflow.com/questions/9086736/why-would-you-use-an-ivar and https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData/EncapsulatingData.html — CodeSmile, Sep 26 '14 at 16:01

score 0 · Answer 1 · answered Sep 26 '14 at 16:06

0

My first thought is that you should declare bouncedFrom as a class variable in the .h rather than declaring it in your init: method.

so in the .h should look like

@interface Ball: NSObject{<br>
    NSString *bouncedFrom;<br>
}

@end

answered Sep 26 '14 at 16:06

Lucian Thorr

1,997
1
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Okay, let's say I made a declaration of Ball: SKSpriteNode. let's say I made a declaration in my .m file: static Ball *ball; How do I access it from didBeginContact ? – Narc0t1CYM Sep 26 '14 at 16:56
When I try to access it from didBeginContact, I'm trying like this : Ball *ball = contact.bodyB.node; But I get this error: Incompatible pointer types initiazing 'BALL *'with an expression of type 'SKNode *' – Narc0t1CYM Sep 26 '14 at 17:00
It's warning you because you can't be sure contact.bodyB.node is of BALL type. You're trying to assign a superclass to a subclass... But you can get rid of the warning with a casting `Ball *ball = (Ball*)contact.bodyB.node;` or if ball is already declared statically: `ball = (Ball*)contact.bodyB.node;` – Lucian Thorr Sep 26 '14 at 20:52

Accessing an object's local variable from a method Objective-c

1 Answers1