Add support for flashScrollIndicators on iOS

[jeanregisser]

Motivation

Flashing scroll indicators is a standard behavior on iOS to show the user there's more content.

Test Plan

Launch RNTester on iOS, go to the ScrollView section, tap the "Flash scroll indicators" button.
You'll see this:

Misc

I've exposed the method flashScrollIndicators on all scrolling components that were already exposing a scrollToXXX method so it's usable from those components using a ref.

Let me know what you think.

[eslint-bot]

semi: Missing semicolon.

[facebook-github-bot]

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[jeanregisser]

@javache let me know if there's anything I can do to make the import succeed.

[javache]

Can you update the ScrollViewExample snapshot test? This is currently breaking tests.

[jeanregisser]

@javache done!

Note: while generating the updated snapshots, I noticed 2 issues:

• I had to fix the RNTester tvOS unit test to link against RCTTest otherwise it didn't compile. (Is it just me?)
• testSliderExample_1@2x.png has not been updated in 295a015
  See the difference for "Custom min/max track tinit color" in testSliderExample_1-iOS10@2x.png and testSliderExample_1@2x.png

Is it still worth it to update non -iOS10 snapshots? Are automated tests only running for iOS10?
Should I open new PR to fix these?

Thanks

[shergin]

I am afraid, we have to redo snapshots one more time... because I changed them.

[jeanregisser]

@shergin what iOS versions did you use to generate the snapshots?

I rebased my changes against the latest master and tried to regenerate the snapshots, but I got more changed snapshots than testScrollViewExample_1*. I used iOS 10.1 and 10.2. and got the same change for both on testSliderExample_1-iOS10@2x.png.

Here is a visual diff: left is original version in master you generated, middle is diff (differences are in red), right is my generated version:

As you can see, the difference is only in the last 2 examples that use a custom track image.
Looking at slider.png and slider-left.png or slider-right.png I see that they have an embedded color profile: Generic RGB Profile.

I'm wondering if the new snapshot infra is dependant on a specific screen color profile.
What's your take on this?

[jeanregisser]

I just tried changing my screen color profile and got the same results as in my initial test.

Also I can see that the example with the thumbs up image uie_thumb_big.png is not affected by the difference. And this one has no color profile embedded.

[shergin]

Oooops, as I mentioned in 3df537a, I changed the way how we make screenshots, and it probably causes your problem. The tests works fine in cloud thought.
I used iPhone 5S and iOS 10.3.

So, should we remove color profile from images?

[jeanregisser]

Ok I'll try tomorrow with 10.3
What about the non iOS10 snapshots? Did you use iOS 9.3? Or else?

[jeanregisser]

Alright @shergin @javache, I got the right output!

For iOS10 snapshots, I used iOS 10.3 on iPhone 5S and Apple TV 10.2 simulators.
For non iOS10 snapshots, I used iOS 9 on iPhone 5S and Apple TV 9.2 simulators.
With these, only the testScrollViewExample_1* were changed, which is expected.

We should probably document what devices and iOS versions are used to generate those snapshots. I had different results using 10.2 or iOS 9.3

[facebook-github-bot]

@javache has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@javache has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[facebook-github-bot]

@shergin has imported this pull request. If you are a Facebook employee, you can view this diff on Phabricator.