从方法访问对象的局部变量Objective-c

我试图从didBeginContact方法访问对象的局部变量。这怎么可能？从方法访问对象的局部变量Objective-c

比方说，我有一个球对象，每当它从球员反弹时，该球的bouncedFrom变量从球员获得一个标识符。

这是我的initBall方法，它初始化一个球。它被称为每3-5（随机）秒。

-(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; 
}

我要的是这样的事情在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]; 
} 
}

两个球xCategories被声明为在我的代码顶部的静态变量。是这样的可能吗？

来源

2014-09-26 Zh4rsiest

你听说过的ivars的，是吗？如果没有：http://stackoverflow.com/questions/9086736/why-would-you-use-an-ivar和https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/ProgrammingWithObjectiveC/EncapsulatingData /EncapsulatingData.html – LearnCocos2D 2014-09-26 16:01:15

我的第一个想法是，你应该在.h中声明bouncedFrom作为类变量，而不是在init：方法中声明它。

所以在.H应该像

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

@end

来源

2014-09-26 16:06:35

好吧，假设我做了Ball：SKSpriteNode的声明。假设我在我的.m文件中做了一个声明：static Ball * ball; 如何从didBeginContact访问它？ – Zh4rsiest 2014-09-26 16:56:49

当我尝试从didBeginContact访问它时，我尝试像这样：Ball * ball = contact.bodyB.node; 但我得到这个错误：不兼容的指针类型使用'SKNode *'类型的表达式初始化'BALL *' – Zh4rsiest 2014-09-26 17:00:27

它警告你，因为你不能确定contact.bodyB.node是BALL类型。你试图将一个超类分配给一个子类... 但是你可以通过铸造来摆脱警告 'Ball * ball =（Ball *）contact.bodyB.node;' 或者如果ball已经静态声明： 'ball =（Ball *）contact.bodyB.node;' – 2014-09-26 20:52:06

从方法访问对象的局部变量Objective-c

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