Question

我从本教程中下载了Ray Wenderlich的简单联系人监听器：http://www.raywenderlich.com/606/how-to-use-box2d-for-just-collision-detection-with-cocos2d-iphone

目前我正在使用下面的代码，它几乎是我在CCLayer中实现Ray的自定义b2ContactListener。但问题是，一次碰撞有多个回调。

有人可以告诉我如何制作它，以便碰撞只会触发一次，直到2个物体都不再触摸然后再润饰？

这是我目前使用的代码：

std::vector<b2Body *>toDestroy; 
std::vector<MyContact>::iterator pos;
for(pos = _contactListener->_contacts.begin(); pos != _contactListener->_contacts.end(); ++pos) {
    MyContact contact = *pos;

    // Get the box2d bodies for each object
    b2Body *bodyA = contact.fixtureA->GetBody();
    b2Body *bodyB = contact.fixtureB->GetBody();
    if (bodyA->GetUserData() != NULL && bodyB->GetUserData() != NULL) {
        CCSprite *spriteA = (CCSprite *) bodyA->GetUserData();
        CCSprite *spriteB = (CCSprite *) bodyB->GetUserData();

        if ((spriteA.tag == 1 && spriteB.tag == 2) || (spriteA.tag == 2 && spriteB.tag == 1)) {
             NSLog(@"tag 1 hit tag 2");
        }

谢谢！

EDIT1：

if ((hasDetectedCollision == NO) && ( (spriteA.tag == 1 && spriteB.tag == 2) || (spriteA.tag == 2 && spriteB.tag == 1) ) ) {
                hasDetectedCollision = YES;
                NSLog(@"tag 1 hit tag 2");
                [self doSomethingWhenCollisionHappens];
            }

- (void)doSomethingWhenCollisionHappens {
    //here you might want to remove an object because of a collision
    //or maybe change the color of the objects that collided
    //I can't provide more details of what you might want
    //to do without seeing more of your code
    //but when you are ready to start receiving collision updates again
    //set hasDetectedCollision to NO again
    [yesLabel setString:[NSString stringWithFormat:@"Yes: %d", yesNumber++]];
    hasDetectedCollision = NO;
}

然后在我的init方法中：

hasDetectedCollision = NO;

新编辑：

if (!hasDetectedCollision && ((spriteA.tag == 1 && spriteB.tag == 4) || (spriteA.tag == 4 && spriteB.tag == 1))) {
            hasDetectedCollision = YES;
            [yesLabel setString:[NSString stringWithFormat:@"Yes:%d", yesInt++]];
            NSLog(@"tag 1 hit tag 4");
        }

Answer 1

我对Box2d并不熟悉，但是根据你在问题中描述的内容，这应该可以帮到你：

在你的.h：

@interface foo : FooBar {
    BOOL hasDetectedCollision;
}

并在你的.m：

- (void)viewDidLoad {
    hasDetectedCollision = NO;
}

然后简单地替换

if ((spriteA.tag == 1 && spriteB.tag == 2) || (spriteA.tag == 2 && spriteB.tag == 1)) {
    NSLog(@"tag 1 hit tag 2");
}

与

if ((hasDetectedCollision == NO) && ( (spriteA.tag == 1 && spriteB.tag == 2) || (spriteA.tag == 2 && spriteB.tag == 1) ) ) {
    hasDetectedCollision = YES;
    NSLog(@"tag 1 hit tag 2");
    [self doSomethingWhenCollisionHappens];
}

然后：

- (void)doSomethingWhenCollisionHappens {
    //here you might want to remove an object because of a collision
    //or maybe change the color of the objects that collided
    //I can't provide more details of what you might want
    //to do without seeing more of your code
    //but when you are ready to start receiving collision updates again
    //set hasDetectedCollision to NO again
    hasDetectedCollision = NO;
}

然后，当您在检测到碰撞时完成您想做的任何事情时，将hasDetectedCollision设置为no，然后重新开始。

编辑：

std::vector<b2Body *>toDestroy; 
std::vector<MyContact>::iterator pos;
for(pos = _contactListener->_contacts.begin(); pos != _contactListener->_contacts.end(); ++pos) {
MyContact contact = *pos;

// Get the box2d bodies for each object
b2Body *bodyA = contact.fixtureA->GetBody();
b2Body *bodyB = contact.fixtureB->GetBody();
if (bodyA->GetUserData() != NULL && bodyB->GetUserData() != NULL) {
    CCSprite *spriteA = (CCSprite *) bodyA->GetUserData();
    CCSprite *spriteB = (CCSprite *) bodyB->GetUserData();

    if(hasDetectedCollision == NO)
        NSLog(@"hasDetectedCollision == NO");

    if ((spriteA.tag == 1 && spriteB.tag == 2) || (spriteA.tag == 2 && spriteB.tag == 1)) {
         NSLog(@"tag 1 hit tag 2");
    }

如果检查hasDetectedCollision状态的if语句被执行，那么问题不在于布尔值，而在于你的碰撞检测。

Answer 2

我不完全确定关于多个答案的SO规则是什么，但这是检查冲突的替代方法，我一直在使用它：

在viewDidLoad方法中：

NSTimer *g = [[NSTimer alloc] initWithFireDate:[NSDate date]
                                      interval:.1
                                        target:self
                                      selector:@selector(checkForCollisions)
                                      userInfo:nil repeats:YES];

NSRunLoop *r = [NSRunLoop currentRunLoop];
[r addTimer:g forMode: NSDefaultRunLoopMode];
[g release];

在checkForCollisions方法中：

//without knowing what you are checking collisions for and
//why you are checking for collisions, I can't be too specific here
//but this code will do what you want

for(someObject* objectOfInterest in yourArrayOfObjectsToBeCompared)) {
    CALayer* layerOne = objectOfInterest.layer.presentationLayer;
    CGRect rectOne = layerOne.frame;
    for(someObject* compareObject in yourArrayOfObjectsToBeCompared) {
        CALayer* layerTwo = compareObject.layer.presentationLayer;
        CGRect rectTwo = layerTwo.frame;
        if(CGRectIntersectsRect(rectOne, rectTwo) && ![compareObject isEqual:objectOfInterest]) {
            //collision detected
        }
    }

此代码只循环遍历您的对象数组以进行比较，然后为每个对象的表示层制作CALayer副本。这一步是至关重要的，因为取对象的常规帧不会给出它当前的位置;这将给出其目的地位置。然后代码再次执行相同的操作，将其与数组中的每个其他对象进行比较。

使用b2ContactListener防止一次碰撞的多次回调？

2 个答案: