This is a workaround for the buggy react-native TextInput multiline on Android. Inspired by the comments on https://github.com/facebook/react-native/issues/12717.

MultilineTextInput.js

import React, {PropTypes, PureComponent} from 'react';
import {TextInput} from 'react-native';
import debounce from 'debounce';

/**
 * This is a workaround for the buggy react-native TextInput multiline on Android.
 *
 * Can be removed once https://github.com/facebook/react-native/issues/12717
 * is fixed.
 *
 * Example for usage:
 *   <MultilineTextInput value={this.state.text} onChangeText={text => setState({text})} />
 */
export default class MultilineTextInput extends PureComponent {
  constructor(props) {
    super(props);
    this.state = {selection: {start: 0, end: 0}};
    // Prevent 2 newlines for some Android versions, because they dispatch onSubmitEditing twice
    this.onSubmitEditing = debounce(this.onSubmitEditing.bind(this), 100, true);
  }
  onSubmitEditing() {
    const {selection} = this.state;
    const {value} = this.props;
    const newText = `${value.slice(0, selection.start)}\n${value.slice(selection.end)}`;
    // move cursor only for this case, because in other cases a change of the selection is not allowed by Android
    if (selection.start !== this.props.value.length && selection.start === selection.end) {
      this.setState({
        selection: {
          start: selection.start + 1,
          end: selection.end + 1,
        },
      });
    }
    this.props.onChangeText(newText);
  }
  render() {
    return (
      <TextInput
        multiline
        blurOnSubmit={false}
        selection={this.state.selection}
        value={this.props.value}
        onSelectionChange={event => this.setState({selection: event.nativeEvent.selection})}
        onChangeText={this.props.onChangeText}
        onSubmitEditing={this.onSubmitEditing}
        {...this.props}
      />
    );
  }
}

MultilineTextInput.propTypes = {
  value: PropTypes.string.isRequired,
  onChangeText: PropTypes.func.isRequired,
};



////////////////// Tests //////////////////



import 'react-native';
// Require after react-native
import renderer from 'react-test-renderer';
import React from 'react';
import {shallow} from 'enzyme';
import MultilineTextInput from '../MultilineTextInput';

describe('MultilineTextInput', () => {
  const text = 'some value';
  const onChangeText = jest.fn();
  const defaultProps = {
    value: text,
    onChangeText,
  };

  it('renders correctly', () => {
    const tree = renderer.create(<MultilineTextInput {...defaultProps} />).toJSON();
    expect(tree).toMatchSnapshot();
  });

  it('inserts a new line at the end if the "enter" soft key is pressed', () => {
    const component = shallow(<MultilineTextInput {...defaultProps} />);
    component.simulate('selectionChange', {nativeEvent: {selection: {start: text.length, end: text.length}}});
    component.simulate('submitEditing');
    expect(onChangeText).toBeCalledWith('some value\n');
  });

  it('inserts a new line in the middle if the cursor is in the middle and the "enter" soft key is pressed', () => {
    const component = shallow(<MultilineTextInput {...defaultProps} />);
    component.simulate('selectionChange', {nativeEvent: {selection: {start: 5, end: 5}}});
    component.simulate('submitEditing');
    expect(onChangeText).toBeCalledWith('some \nvalue');
  });

  it('inserts a new line in the middle if text is selected and the "enter" soft key is pressed', () => {
    const component = shallow(<MultilineTextInput {...defaultProps} />);
    component.simulate('selectionChange', {nativeEvent: {selection: {start: 4, end: 7}}});
    component.simulate('submitEditing');
    expect(onChangeText).toBeCalledWith('some\nlue');
  });
});

Hey, thanks for this work!
I ran into a little issue with it when I'm using it while handling selection changes myself.

To fix those I had to add:

componentWillReceiveProps(props) {
    if (props.selection) {
        this.setState({ selection: props.selection });
    }
}
focus() {
    this.refs.text.focus();
}

And change onSubmitEditting to:

onSubmitEditing() {
    const { selection } = this.state;
    const { value } = this.props;
    const newText = `${value.slice(0, selection.start)}\n${value.slice(selection.end)}`;
    
    this.props.onChangeText(newText);
    
    // move cursor only for this case, because in other cases a change of the selection is not allowed by Android
    if (selection.start !== this.props.value.length && selection.start === selection.end) {
        const newSelection = {
            selection: {
                start: selection.start + 1,
                end: selection.end + 1,
            },
        };
        if (this.props.onSelectionChange) {
            this.props.onSelectionChange({ nativeEvent: newSelection });
        } else {
            this.setState(newSelection);
        }
    }
}

Essentially, I'm allowing the container to manage the selection state themselves.

Here's the updated code
https://gist.github.com/codewithpassion/d2d1a3e4d94c547e6b343ea5e9fe9845