prevent scheduling unnecessary layoutanimation

[koenpunt]

Motivation

when a hardware keyboard is connected, the virtual keyboard can be hidden (this can easily be demonstrated in the simulator), which means the height of the keyboard is 0. When in this case a LayoutAnimation is scheduled, the KeyboardAvoidingView won't be affected, but the next layout change will be animated, which can have unintended side-effects. This can also trigger the Overriding previous layout animation with new one before the first began warning.

Screenshot

Test Plan

Open the KeyboardAvoidingView example in the RNTester project, import LayoutAnimation and add something rendered conditionally to the content of the Modal, e.g.;

{this.state.behavior === 'position' &&
  <Text>We're using position now</Text>
}

Then update the onSegmentChange handler with a LayoutAnimation;

onSegmentChange = (segment: String) => {
  LayoutAnimation.easeInEaseOut();
  this.setState({behavior: segment.toLowerCase()});
};

Now open the example in the simulator and play with the "Toggle Software Keyboard" option;

Now when you focus the input, no keyboard should appear, and when you then press an option of the segmented control, you should get the beforementioned warning.

After this change this warning will no longer appear, but the component still behaves the same as before.

Release Notes

[IOS] [BUGFIX] [KeyboardAvoidingView] - prevent scheduling unnecessary LayoutAnimation

[pull-bot]

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