[iOS] Fixes ScrollView centerContent not work in some cases

[zhongwuzw]

Summary

The bug description can see #24688, we add contentView size check before center the content, because in some cases, the contentView's size not yet be calculated, in those cases, we don't adjust the contentOffset.

cc. @cpojer .

Changelog

[iOS] [Fixed] - Fixes ScrollView centerContent not work in some cases

Test Plan

centerContent can works on iPhoneX when using the code like below:

import React, {Component} from 'react';
import {ScrollView, View} from 'react-native';

export default class App extends Component {
    render() {
        return (
            <View
                style={{
                    flex: 1,
                    backgroundColor: "blue",
                    justifyContent: "center",
                    alignItems: "center",
                    flexDirection: "row"
                }}
            >
                <View style={{width: 100,
                    backgroundColor: "red",
                    height: 400}}>
                    <ScrollView
                        contentContainerStyle={{justifyContent: "center", alignItems: "center"}}
                        style={{backgroundColor: "green"}}
                        centerContent={true}
                    >
                        <View style={{backgroundColor: "orange", width: 50, height: 50}} />
                    </ScrollView>
                </View>
                <View style={{width: 100,
                    backgroundColor: "indigo",
                    height: 400}}>
                    <ScrollView
                        contentContainerStyle={{justifyContent: "center", alignItems: "center"}}
                        style={{backgroundColor: "purple"}}
                        centerContent={true}
                    >
                        <View style={{backgroundColor: "violet", width: 50, height: 50}} />
                    </ScrollView>
                </View>
            </View>
        );
    }
}

[sahrens]

Thanks!

[facebook-github-bot]

@sahrens is landing this pull request. If you are a Facebook employee, you can view this diff on Phabricator.

[react-native-bot]

This pull request was successfully merged by @zhongwuzw in 2cdf969.

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