Add checkbox component.

components/createCheckboxComponent/index.tsx

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+import * as React from "react";
+import { StyleSheet, View, Text, ViewStyle, TextStyle } from "react-native";
+import type { CheckboxStateStyle } from "../../types/CheckboxStateStyle";
+import type { CheckboxStyle } from "../../types/CheckboxStyle";
+import { Hitbox } from "../Hitbox";
+
+const createViewStyle = (
+  checkboxStyle: CheckboxStyle,
+  checkboxStateStyle: CheckboxStateStyle
+): ViewStyle => {
+  const output: ViewStyle = {
+    backgroundColor: checkboxStateStyle.backgroundColor,
+    width: checkboxStyle.boxSize,
+    height: checkboxStyle.boxSize,
+    justifyContent: `center`,
+    alignItems: `center`,
+  };
+
+  if (checkboxStateStyle.border !== null) {
+    output.borderWidth = checkboxStateStyle.border.width;
+    output.borderColor = checkboxStateStyle.border.color;
+  }
+
+  if (checkboxStateStyle.radius !== 0) {
+    output.borderRadius = checkboxStateStyle.radius;
+  }
+
+  const relativeBorderWidth =
+    (checkboxStyle.enabledFalse.border === null
+      ? 0
+      : checkboxStyle.enabledFalse.border.width) -
+    (checkboxStateStyle.border === null ? 0 : checkboxStateStyle.border.width);
+
+  if (relativeBorderWidth !== 0) {
+    output.margin = relativeBorderWidth;
+  }
+
+  return output;
+};
+
+const createTextStyle = (
+  checkboxStyle: CheckboxStyle,
+  checkboxStateStyle: CheckboxStateStyle
+): TextStyle => {
+  const output: TextStyle = {
+    fontFamily: checkboxStyle.fontFamily,
+    fontSize: checkboxStyle.fontSize,
+    lineHeight: checkboxStyle.fontSize * 1.4,
+    color: checkboxStateStyle.color,
+  };
+
+  if (checkboxStyle.boxLabelSpacing !== 0) {
+    output.paddingLeft = checkboxStyle.boxLabelSpacing;
+  }
+
+  return output;
+};
+
+/**
+ * Creates a React component representing a form checkbox.
+ * @param checkboxStyle The style to apply to the checkbox.
+ * @returns             The created React component.
+ */
+export const createCheckboxComponent = (
+  checkboxStyle: CheckboxStyle
+): React.FunctionComponent<{
+  /**
+   * When true, the checkbox is checked.  It is otherwise unchecked.
+   */
+  value: boolean;
+
+  /**
+   * Invoked when the checkbox is pressed.
+   * @param to True when the checkbox is changing from unchecked to checked,
+   *           otherwise, false.
+   */
+  onChange(to: boolean): void;
+
+  /**
+   * When true, the checkbox will show alternative styles and will not accept
+   * input.  It will otherwise show its default styles and accept input.
+   */
+  disabled: boolean;
+}> => {
+  const styles = StyleSheet.create({
+    hitbox: {
+      width: `100%`,
+      flexDirection: `row`,
+    },
+    disabledFalseView: createViewStyle(
+      checkboxStyle,
+      checkboxStyle.disabledFalse
+    ),
+    disabledTrueView: createViewStyle(
+      checkboxStyle,
+      checkboxStyle.disabledTrue
+    ),
+    enabledFalseView: createViewStyle(
+      checkboxStyle,
+      checkboxStyle.enabledFalse
+    ),
+    enabledTrueView: createViewStyle(checkboxStyle, checkboxStyle.enabledTrue),
+    disabledFalseText: createTextStyle(
+      checkboxStyle,
+      checkboxStyle.disabledFalse
+    ),
+    disabledTrueText: createTextStyle(
+      checkboxStyle,
+      checkboxStyle.disabledTrue
+    ),
+    enabledFalseText: createTextStyle(
+      checkboxStyle,
+      checkboxStyle.enabledFalse
+    ),
+    enabledTrueText: createTextStyle(checkboxStyle, checkboxStyle.enabledTrue),
+  });
+
+  return ({ value, onChange, disabled, children }) => (
+    <Hitbox
+      disabled={disabled}
+      onPress={() => {
+        onChange(!value);
+      }}
+      style={styles.hitbox}
+    >
+      <View
+        style={
+          value
+            ? disabled
+              ? styles.disabledTrueView
+              : styles.enabledTrueView
+            : disabled
+            ? styles.disabledFalseView
+            : styles.enabledFalseView
+        }
+      >
+        {value
+          ? disabled
+            ? checkboxStyle.disabledTrue.boxChild
+            : checkboxStyle.enabledTrue.boxChild
+          : disabled
+          ? checkboxStyle.disabledFalse.boxChild
+          : checkboxStyle.enabledFalse.boxChild}
+      </View>
+      <Text
+        style={
+          value
+            ? disabled
+              ? styles.disabledTrueText
+              : styles.enabledTrueText
+            : disabled
+            ? styles.disabledFalseText
+            : styles.enabledFalseText
+        }
+      >
+        {children}
+      </Text>
+    </Hitbox>
+  );
+};

components/createCheckboxComponent/readme.md

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+# `react-native-app-helpers/createCheckboxComponent`
+
+Creates a React component representing a form checkbox.
+
+## Usage
+
+```tsx
+import { createCheckboxComponent } from "react-native-app-helpers";
+
+const ExampleCheckbox = createCheckboxComponent({
+  fontFamily: `Example Font Family`,
+  fontSize: 16,
+  boxSize: 14,
+  boxLabelSpacing: 5,
+  disabledFalse: {
+    backgroundColor: 'blue',
+    color: 'yellow',
+    boxChild: <Text>DF</Text>,
+    radius: 3,
+    border: {
+      width: 5,
+      color: `red`,
+    },
+  },
+  disabledTrue: {
+    backgroundColor: 'blue',
+    color: 'yellow',
+    boxChild: <Text>DT</Text>,
+    radius: 3,
+    border: {
+      width: 5,
+      color: `red`,
+    },
+  },
+  enabledFalse: {
+    backgroundColor: 'blue',
+    color: 'yellow',
+    boxChild: <Text>EF</Text>,
+    radius: 3,
+    border: {
+      width: 5,
+      color: `red`,
+    },
+  },
+  enabledTrue: {
+    backgroundColor: 'blue',
+    color: 'yellow',
+    boxChild: <Text>ET</Text>,
+    radius: 3,
+    border: {
+      width: 5,
+      color: `red`,
+    },
+  },
+});
+
+const ExampleScreen = () => {
+  const [value, setValue] = React.useState(false);
+
+  return (
+    <ExampleCheckbox value={value} onChange={setValue} disabled={false}>
+      Example Label
+    </ExampleCheckbox>
+  );
+};
+```