asObservableFor causes a crash if the property value is nil

[serieuxchat]

I have a class Person with a property commonName. In some cases the value of this property is nil.

If I would like to watch this property, I do the following:

// Suppose that p is of type Person
var commonNameDynamic = Dynamic.asObservableFor(p, keyPath: "commonName")

This causes a crash if the value of commonName is nil.

[srdanrasic]

Hi Sergey,

Can you try specifying the type as optional String and let me know if it helps:

let commonNameDynamic = Dynamic<String?>.asObservableFor(p, keyPath: "commonName")

You'll need to map it to non-optional when binding it to label.

commonNameDynamic.map { $0 ?? "" } ->> commonNameLabel

Also, aim for making your Dynamics as constants (using let keyword) instead of variables.

[serieuxchat]

Just tried it. Unfortunately, it still crashes...

Thanks for making such an awesome framework, btw! (we'll iron out these small things, I am sure; as for the rest, it just rocks!)

[serieuxchat]

I guess, the problem is here:
let dynamic = InternalDynamic((object.valueForKeyPath(keyPath) as? T)!, faulty: false)

valueForKeyPath gives back nil, and then there is a forced unwrap, right?

[srdanrasic]

Thank you!

Yeah, that looks like a problem. Working on fix right now...

[serieuxchat]

Thanks, mate!

[serieuxchat]

Hi Srđan,
So far I have come up with the following work-around (added a method that also accepts a default value - to be used in case the property is nil)

public class func asObservableFor(object: NSObject, keyPath: String, defaultValue: T) -> Dynamic<T> 
{
    let keyPathValue: AnyObject? = object.valueForKeyPath(keyPath)
    let value: T = (keyPathValue != nil) ? (keyPathValue as? T)! : defaultValue
    let dynamic = InternalDynamic(value, faulty: false)

    let helper = DynamicKVOHelper(keyPath: keyPath, object: object as NSObject) {
        [unowned dynamic] (v: AnyObject) -> Void in

        if (v is NSNull)
        {
            dynamic.value = defaultValue
        }
        else
        {
            dynamic.value = (v as? T)!
        }
    }

    dynamic.retain(helper)
    return dynamic
}

[srdanrasic]

Yeah, it's pain looks like. I don't see a way to do it without defaultValue. If you want, you can do pull request with your update.

[serieuxchat]

I will think a little more about it, but for now, I guess, it would do with the defaultValue approach.
Are you going to keep the second version of the method or always require a default value (if you do a pull request)?

It also looks like it's currently not possible to have an update go in the other direction (with some property of NSObject) I.e. if I want to have person.commonName updated automatically whenever a user types something into some corresponding text field... (In this case the property is not a dynamic and must be updated with setValue:forKeyPath, right?)

[srdanrasic]

Its a good question, I'll give it some more thought tonight.

Two way binding with KVO property should also be doable by having feedback bond like this:

  ...

  let feedbackBond = Bond<T>() { [unowned object] value in
    object.setValue(value, forKey: keyPath)
  }

  dynamic.bindTo(feedbackBond, fire: false, strongly: false)
  dynamic.retain(feedbackBond)

  dynamic.retain(helper)
  return dynamic

But there are some problems with types I need to fix first...

[srdanrasic]

Default value should always be needed to prevent unintentional bugs.

[srdanrasic]

Thanks for your help @serieuxchat . I've fixed this in v3.0.1 with your suggestion.

Additionally, I added another way to create Dynamic representations of K-V observed properties which is to be used for two-way bindings. Checkout README.

[serieuxchat]

Awesome!
Thanks a lot for reacting so quickly!

I am sure, the framework will get used a lot. You've done a beautiful thing! Thanks again for the effort and the love you've put into this.

Kind regards,
Sergey

On 4 mrt. 2015, at 22:37, Srđan Rašić notifications@github.com wrote:

Thanks for your help @serieuxchat . I've fixed this in v3.0.1 with your suggestion.

Additionally, I added another way to create Dynamic representations of K-V observed properties which is to be used for two-way bindings. Checkout README.

—
Reply to this email directly or view it on GitHub.

[srdanrasic]

You're welcome! Should you find any more issues, feel free to open another issue.