Wednesday, September 10, 2014

Matching custom NSObject with isEqual and hash

While working on one multiplayer game for iOS using GameKit, I faced issue while comparing object.

For single player version I was not facing this issue but while running multiplayer version I was facing this issue. After debugging a little I realised condition for comparing object's value is failing and it turned out that I was comparing object's address rather then its value. As for Multiplayer game I was creating object using data from server/host, I needed to compare object's value and not its address.

For objectiveC, if you want to compare object's value using "==" operator, you need to overload isEqual and hash method as shown like below.

-(BOOL)isEqual:(id) other {
    if (other == self)
        return YES;
    if (!other || ![other isKindOfClass:[self class]])
        return NO;
    Card* otherCard = other;
    return ( mSuit == otherCard.mSuit && mRank == otherCard.mRank);

- (NSUInteger)hash {
    NSUInteger hash = 0;
    hash += [[NSNumber numberWithInt:mSuit] hash];
    hash += [[NSNumber numberWithInt:mRank] hash];
    return hash;
Note that you need to overload both method together, overloading only one will not work. Once I overloaded above method my multiplayer version started working as normal.

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