Why Are Didbegincontact Called Multiple Times

Why are didBeginContact called multiple times?

I had the same problem (score increasing multiple times for a single enemy destroyed and multiple life points being lost for a single instance of damage.) A user on the Apple forums thinks that it's a bug in [SKPhysicsBody bodyWithTexture:size:] but I don't believe that's the case, because it was happening with other constructors too.

First off, the categoryBitMask and contactTestBitMask are very important, obviously. Take a look at Apple's SpriteKit Physics Collisions sample code:

// Contacts are often a double dispatch problem; the effect you want is based on the type of both bodies in the contact. This sample this in a brute force way, by checking the types of each. A more complicated example might use methods on objects to perform the type checking.

// The contacts can appear in either order, and so normally you'd need to check
each against the other. In this example, the category types are well ordered, so
the code swaps the two bodies if they are out of order. This allows the code
to only test collisions once.

What I did to solve it was setting a flag after handling each condition. In my case, I was testing whether bodyA.node.parent was nil in didBeginContact, because I called removeFromParent() on the missile/enemy nodes to destroy them.

I think you should expect the event to fire multiple times and your code in there has to make sure it's processed only once.

Why are didBeginContact called multiple times?

I had the same problem (score increasing multiple times for a single enemy destroyed and multiple life points being lost for a single instance of damage.) A user on the Apple forums thinks that it's a bug in [SKPhysicsBody bodyWithTexture:size:] but I don't believe that's the case, because it was happening with other constructors too.

First off, the categoryBitMask and contactTestBitMask are very important, obviously. Take a look at Apple's SpriteKit Physics Collisions sample code:

// Contacts are often a double dispatch problem; the effect you want is based on the type of both bodies in the contact. This sample this in a brute force way, by checking the types of each. A more complicated example might use methods on objects to perform the type checking.

// The contacts can appear in either order, and so normally you'd need to check
each against the other. In this example, the category types are well ordered, so
the code swaps the two bodies if they are out of order. This allows the code
to only test collisions once.

What I did to solve it was setting a flag after handling each condition. In my case, I was testing whether bodyA.node.parent was nil in didBeginContact, because I called removeFromParent() on the missile/enemy nodes to destroy them.

I think you should expect the event to fire multiple times and your code in there has to make sure it's processed only once.

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