從方法訪問對象的局部變量Objective-c

我試圖從didBeginContact方法訪問對象的局部變量。這怎麼可能？從方法訪問對象的局部變量Objective-c

比方說，我有一個球對象，每當它從球員反彈時，該球的bouncedFrom變量從球員獲得一個標識符。

這是我的initBall方法，它初始化一個球。它被稱爲每3-5（隨機）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; 
}

我要的是這樣的事情在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]; 
} 
}

兩個球xCategories被聲明爲在我的代碼頂部的靜態變量。是這樣的可能嗎？

來源

2014-09-26 Zh4rsiest

你聽說過的ivars的，是嗎？如果沒有：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

我的第一個想法是，你應該在.h中聲明bouncedFrom作爲類變量，而不是在init：方法中聲明它。

所以在.H應該像

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

@end

來源

2014-09-26 16:06:35

好吧，假設我做了Ball：SKSpriteNode的聲明。假設我在我的.m文件中做了一個聲明：static Ball * ball; 如何從didBeginContact訪問它？ – Zh4rsiest 2014-09-26 16:56:49

當我嘗試從didBeginContact訪問它時，我嘗試像這樣：Ball * ball = contact.bodyB.node; 但我得到這個錯誤：不兼容的指針類型使用'SKNode *'類型的表達式初始化'BALL *' – Zh4rsiest 2014-09-26 17:00:27

它警告你，因爲你不能確定contact.bodyB.node是BALL類型。你試圖將一個超類分配給一個子類... 但是你可以通過鑄造來擺脫警告 'Ball * ball =（Ball *）contact.bodyB.node;' 或者如果ball已經靜態聲明： 'ball =（Ball *）contact.bodyB.node;' – 2014-09-26 20:52:06

從方法訪問對象的局部變量Objective-c

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