react-navigation-stack/lib/module/vendor/views/Header/HeaderBackButton.js

Stack navigator component for React Navigation

import * as React from 'react';
import { Animated, I18nManager, Image, View, Platform, StyleSheet } from 'react-native';
import MaskedView from '../MaskedView';
import TouchableItem from '../TouchableItem';
import useTheme from '../../../utils/useTheme';
export default function HeaderBackButton({
  disabled,
  allowFontScaling,
  backImage,
  label,
  labelStyle,
  labelVisible = Platform.OS === 'ios',
  onLabelLayout,
  onPress,
  pressColorAndroid: customPressColorAndroid,
  screenLayout,
  tintColor: customTintColor,
  titleLayout,
  truncatedLabel = 'Back',
  accessibilityLabel = label && label !== 'Back' ? "".concat(label, ", back") : 'Go back',
  style
}) {
  const {
    dark,
    colors
  } = useTheme();
  const [initialLabelWidth, setInitialLabelWidth] = React.useState(undefined);
  const tintColor = customTintColor !== undefined ? customTintColor : Platform.select({
    ios: colors.primary,
    default: colors.text
  });
  const pressColorAndroid = customPressColorAndroid !== undefined ? customPressColorAndroid : dark ? 'rgba(255, 255, 255, .32)' : 'rgba(0, 0, 0, .32)';

  const handleLabelLayout = e => {
    onLabelLayout === null || onLabelLayout === void 0 ? void 0 : onLabelLayout(e);
    setInitialLabelWidth(e.nativeEvent.layout.x + e.nativeEvent.layout.width);
  };

  const shouldTruncateLabel = () => {
    return !label || initialLabelWidth && titleLayout && screenLayout && (screenLayout.width - titleLayout.width) / 2 < initialLabelWidth + 26;
  };

  const renderBackImage = () => {
    if (backImage) {
      return backImage({
        tintColor
      });
    } else {
      return /*#__PURE__*/React.createElement(Image, {
        style: [styles.icon, Boolean(labelVisible) && styles.iconWithLabel, Boolean(tintColor) && {
          tintColor
        }],
        source: require('../assets/back-icon.png'),
        fadeDuration: 0
      });
    }
  };

  const renderLabel = () => {
    const leftLabelText = shouldTruncateLabel() ? truncatedLabel : label;

    if (!labelVisible || leftLabelText === undefined) {
      return null;
    }

    const labelElement = /*#__PURE__*/React.createElement(View, {
      style: screenLayout ? // We make the button extend till the middle of the screen
      // Otherwise it appears to cut off when translating
      [styles.labelWrapper, {
        minWidth: screenLayout.width / 2 - 27
      }] : null
    }, /*#__PURE__*/React.createElement(Animated.Text, {
      accessible: false,
      onLayout: // This measurement is used to determine if we should truncate the label when it doesn't fit
      // Only measure it when label is not truncated because we want the measurement of full label
      leftLabelText === label ? handleLabelLayout : undefined,
      style: [styles.label, tintColor ? {
        color: tintColor
      } : null, labelStyle],
      numberOfLines: 1,
      allowFontScaling: !!allowFontScaling
    }, leftLabelText));

    if (backImage || Platform.OS !== 'ios') {
      // When a custom backimage is specified, we can't mask the label
      // Otherwise there might be weird effect due to our mask not being the same as the image
      return labelElement;
    }

    return /*#__PURE__*/React.createElement(MaskedView, {
      maskElement: /*#__PURE__*/React.createElement(View, {
        style: styles.iconMaskContainer
      }, /*#__PURE__*/React.createElement(Image, {
        source: require('../assets/back-icon-mask.png'),
        style: styles.iconMask
      }), /*#__PURE__*/React.createElement(View, {
        style: styles.iconMaskFillerRect
      }))
    }, labelElement);
  };

  const handlePress = () => onPress && requestAnimationFrame(onPress);

  return /*#__PURE__*/React.createElement(TouchableItem, {
    disabled: disabled,
    accessible: true,
    accessibilityRole: "button",
    accessibilityComponentType: "button",
    accessibilityLabel: accessibilityLabel,
    accessibilityTraits: "button",
    testID: "header-back",
    delayPressIn: 0,
    onPress: disabled ? undefined : handlePress,
    pressColor: pressColorAndroid,
    style: [styles.container, disabled && styles.disabled, style],
    hitSlop: Platform.select({
      ios: undefined,
      default: {
        top: 16,
        right: 16,
        bottom: 16,
        left: 16
      }
    }),
    borderless: true
  }, /*#__PURE__*/React.createElement(React.Fragment, null, renderBackImage(), renderLabel()));
}
const styles = StyleSheet.create({
  container: {
    alignItems: 'center',
    flexDirection: 'row',
    ...Platform.select({
      ios: null,
      default: {
        marginVertical: 3,
        marginHorizontal: 11
      }
    })
  },
  disabled: {
    opacity: 0.5
  },
  label: {
    fontSize: 17,
    // Title and back label are a bit different width due to title being bold
    // Adjusting the letterSpacing makes them coincide better
    letterSpacing: 0.35
  },
  labelWrapper: {
    // These styles will make sure that the label doesn't fill the available space
    // Otherwise it messes with the measurement of the label
    flexDirection: 'row',
    alignItems: 'flex-start'
  },
  icon: Platform.select({
    ios: {
      height: 21,
      width: 13,
      marginLeft: 8,
      marginRight: 22,
      marginVertical: 12,
      resizeMode: 'contain',
      transform: [{
        scaleX: I18nManager.isRTL ? -1 : 1
      }]
    },
    default: {
      height: 24,
      width: 24,
      margin: 3,
      resizeMode: 'contain',
      transform: [{
        scaleX: I18nManager.isRTL ? -1 : 1
      }]
    }
  }),
  iconWithLabel: Platform.OS === 'ios' ? {
    marginRight: 6
  } : {},
  iconMaskContainer: {
    flex: 1,
    flexDirection: 'row',
    justifyContent: 'center'
  },
  iconMaskFillerRect: {
    flex: 1,
    backgroundColor: '#000'
  },
  iconMask: {
    height: 21,
    width: 13,
    marginLeft: -14.5,
    marginVertical: 12,
    alignSelf: 'center',
    resizeMode: 'contain',
    transform: [{
      scaleX: I18nManager.isRTL ? -1 : 1
    }]
  }
});
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