#isequal:

[antonio081014]

How to compare objects of your custom NSObject subclass?

Comparison of any two NSObject objects or the objects of NSObject subclass could be very useful, when you are sorting, being unique in collection, or other cases. For example, you need to have your NSObject subclass objects added to or removed from a NSMutableSet, the Set needs to well identify which object is which, so there will be no duplicates. Then, the comparison of objects will be used to help.

How can we do it? Simple.

1st, Overwrite isEqual:(id)object function.

- (BOOL)isEqual:(id)object { if ([object isKindOfClass:[DeviceSensorStruct class]]) { DeviceSensorStruct *obj1 = (DeviceSensorStruct *)object; if (self.deviceID == obj1.deviceID && self.sensorID == obj1.sensorID) { return YES; } else { return NO; } } return NO; }

2nd, Give your object a meaning ful hash value.

- (NSUInteger)hash { return (int)(self.deviceID) * sizeof(unsigned char) + (int)(self.sensorID); }

[findnerd-blog]

Difference between "==" and "isEqual:" in objective C

These two operators or function can be used to check equity of objects or operands. "==" is used to check if pointer values of objects are same. However "isEqual:" is used to test if both objects are having same values. So "==" works on reference and "isEqual" works on value. It can be easily understand by following example:

NSMutableArray *array1 = [[NSMutableArray alloc]initWithObjects:@"A", @"B", nil];

NSMutableArray *array2 = [[NSMutableArray alloc]initWithObjects:@"A", @"B", nil];

if (array1 == array2) {

       NSLog(@"==");

   }

if ([array1 isEqual:array2]) {

       NSLog(@"isequal");

   }

It will print "isEqual" because pointer values for both array1 and array2 are different

Second case:

NSMutableArray *array1 = [[NSMutableArray alloc]initWithObjects:@"A", @"B", nil];

NSMutableArray *array2 = [[NSMutableArray alloc]init];

array2 = array1;

if (array1 == array2) {

       NSLog(@"======");

   }

if ([array1 isEqual:array2]) {

       NSLog(@"isequal");

   }

It will print "isEqual" and "==" because reference and value for both array1 and array2 are same

Third case:

NSMutableArray *array1 = [[NSMutableArray alloc]initWithObjects:@"A", @"B", nil];

NSMutableArray *array2 = [[NSMutableArray alloc]init];

array2 = [array1 mutableCopy];

   [array1 addObject:@"C"];

   if (array1 == array2) {

       NSLog(@"======");

   }

   if ([array1 isEqual:array2]) {

       NSLog(@"isequal");

   }

It will print nothing because reference and value for both array1 and array2 are changed.

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