Errors with inheritance and contructors about parceler

[johncarl81]

Thanks for the feedback @ahem, I'll have to look at your proposal. An error should be given in the example you gave that there is no default empty constructor and you do not have a constructor annotated. In order to get this to work, you will need to annotate the constructor you want to use in the given class, like so:

@Parcel
public class AClass {
    String message;
    public final String getMessage() { return this.message; }
    public void setMessage(String message) { this.message = message; }

    @ParcelConstructor
    public AClass(String message) {
        this.message = message;
    }
}

@Parcel
public class ASubClass extends AClass {
    int status;
    public int getStatus() { return status; }
    public void setStatus(int status) { this.status = status; }

    @ParcelConstructor
    public ASubClass(String message, int status) {
        super(message);
        this.status = status;
    }
}

Is the problem that Parceler is not associating the "message" parameter between the constructor parameter and the super classes' field?

[ahem]

Interestingly AClass works just fine without the @ParcelConstructor annotation. It seems that, when there is only one constructor defined on the class, then parceller defaults to that and doesn't require the annotation (at least, that is what I think this bit does: ParcelableAnalysis:258).

But, anyway, as you say, constructor annotation or no constructor annotation, when I add the subclass then the project doesn't compile anymore, and fails with this error:

Parceler: Accessor not found for property message

I can understand that this happens because there is no accessor defined for the message property in ASubClass, but there is one available in the base class, so I would think parceler would just use that?

[johncarl81]

Looking at this issue in depth. I can reproduce it and confirm that this not the expected behavior of Paceler.

First, you should be required to annotate the constructor you want to use if a single empty constructor (or default constructor) doesn't exist. Otherwise this should flag an error. Parceler does not automatically decide which constructor is appropriate to use, it needs your direction. The code you highlighted does part of that, it looks for a single empty constructor, the code that flags the error just doesn't exist (yet).

Second, and this is where I would like feedback from you @ahem, associating constructor parameters with properties in the inheritance hierarchy of a bean presents a challenge. At each level of the class hierarchy, Parceler requires the classes' properties (defined by either fields, methods or manually annotated) to be uniquely named. This is easy to enforce because you cannot name a field or method the same thing twice. Constructor parameters must match some reader in the class. This allows Parceler to write the value in the constructor and read it back from a field or method. Right now constructor parameters may only match the same hierarchy level properties. If we were to match on all hierarchy levels, we would need to check for uniqueness across the entire hierarchy. I can see a couple solutions to this:

1. All Constructor Parameters must have unique readers across all levels of inheritance.
2. Constructor Parameters match the highest hierarchy level property reader, if duplicates exist

I'm starting to lean towards matching the highest level reader because we would not have to do a deep duplicate check.

What are your thoughts on this?

[ahem]

I think that the way constructor parameters are supported now is very easy to understand - it seems very natural that you just have to name the parameter the same as the field or getter function, and then Parceler automatically connects them.

I really would like it if Parceler would match property accessors on other hierarchy levels, though, and I agree with you that the best way to handle duplicated property names would be to use the accessor on the highest level.

[johncarl81]

I decided to go with option 1 as it's less mysterious and easier to fix when problems come up. I also was able to make your use case pass, with the @ParcelConstructor parameters added. I've deployed the Parceler SNAPSHOT to maven central under 0.2.8-SNAPSHOT, could you give it a try and let me know if it works for you?

[johncarl81]

@ahem I'm thinking about cutting a release soon, I'd appreciate your feedback before then.

[johncarl81]

Closing this issue, feel free to reopen if this fix didn't work.

[ahem]

@johncarl81 Sorry for the delayed feedback - I was on vacation over easter, and internet access turned out to be pretty difficult to find.

Anyways, I have tested you changes and they work perfectly. Thank you very much for the quick response and fix :-)

[johncarl81]

Fantastic. Thank you for reporting it!