Observation without initial value about block-kvo HOT 4 CLOSED

No, there is not. Initial value is desired in all cases I have ever encountered. Why do you need it?

You can skip the first by using __block counter outside of the the observation.

from block-kvo.

@iMartinKiss, I would like to disable initial value observation for an object that represents a remote device. This object is KVO'd for updating values on the remote device. However, the initial values of nil and 0 really can be ignored as they shouldn't be written back to the device. Currently, I have to add a check around every single property of that remote device to make sure the initial value doesn't get sent to the remote device.

If observation without the initial value existed then I could remove a bunch of unnecessary conditional checks and rely on my own manual KVO triggering after the properties of the remote object had loaded. I already disable automatic KVO but the initial value observation is still a problem.

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Few weeks ago I was also working with remote devices and similarily sending KVO changes through MCSession, but I had no problem with initial values. I had two cases:

1. At the moment of registering observation the device was not yet connected, so attempt to send initial value was ignored.
2. At the moment of registering observation the device was connected and there already was a valid value in property. This way the device immediately received existing value, not just future changes.

However, I used coalescing for these updates, so they were sent in batches and I used nil as unknown value, so it indicated nothing was received yet (on the remote device).

Anyway you can simply create a wrapping method that chacks for initial calback:

- (void)observePropertyWithoutInitialValue:(NSString *)keyPath withBlock:(MTKBlockChange)observationBlock {
    __block BOOL isInitial = YES;
    [self observeProperty:keyPath withBlock:^(__weak id weakSelf, id old, id new) {
        if (isInitial) {
            isInitial = NO;
        }
        else {
            observationBlock(weakSelf, old, new);
        }
    }];
}

from block-kvo.

Thanks for the reply @iMartinKiss. I am currently using an uglier version of your suggested wrapper method, so I'll be updating that. Any chance of that being added to Block-KVO? That seems like it should be a part of the library rather than people piecemeal adding it.

Regarding 1 above, I'm worried about having a coincidental dependency in code where it happens to work out because the device isn't connected. I'm not sure this will always be the case. Need to think about this more.

Regarding 2 above, unfortunately, it's likely to not be true in my case where valid values exist upon connection.

Thanks again, Block-KVO has been a wonderful help.

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