fix(ios): undefined is not an object (evaluating 'measureSpec.setColumn')

[m-abs]

We, the rest of the NativeScript community, thank you for your
contribution!
To help the rest of the community review your change, please follow the instructions in the template.
-->

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/NativeScript/blob/master/DevelopmentWorkflow.md#running-unit-tests.
• [ ] Tests for the changes are included - https://github.com/NativeScript/NativeScript/blob/master/WritingUnitTests.md

What is the current behavior?

In the past month we've tracked 20+ crashes with this error:

TypeError: undefined is not an object (evaluating 'measureSpec.setColumn')

We haven't been able to consistently reproduce the crash locally, but I think it is clear where it does wrong.

What is the new behavior?

GridLayout(ios).onMeasure(...) will create MeasureSpecs if missing the for child view when it calls this.eachLayoutChild(...)

Fixes: #7226

[manoldonev]

I was reviewing our code and I am not sure trying to fix this exceptional situation by registering layout child here is a good idea. How about just skipping this specific layout child instead (as obviously something is not right with its current state)?

if (!measureSpecs) { 
    continue;
}

[m-abs]

I've finally managed to reproduce the problem see: #7226 (comment)

I'm not sure what the best solution is or if we just use components+layouts incorrectly.

Just skipping as you suggest results in the component not being rendered.

[manoldonev]

hey @m-abs thank you isolating the problem!
So just skipping the iteration when measureSpec is undefined is not an option, ok. Will investigate the code on the nativescript-angular side a bit but if I don't find a better solution I am going to merge yours as is.

Meanwhile, there is also a workaround that you can use -- wrap the contents of your sub1 component (sub1.component.html) in any kind of layout like this:

<GridLayout>
    <ns-sub2></ns-sub2>
</GridLayout>

[manoldonev]

@m-abs I think we found the root of the problem in the ProxyViewContainer class -- see my commit here: 3acfc70

[m-abs]

Looks good to me.

[manoldonev]

test