react-native-signature-canvas

React Native Signature Component based Canvas for Android && IOS && expo

• Supports Android and iOS and Expo
• Tested with RN 0.69
• Core use signature_pad.js
• Generates a base64 encoded png image of the signature Note: Expo support for React Native Signature Canvas v1.5.0 started with Expo SDK v33.0.0.

Installation(for React Native V0.60.0 or Expo SDK v35.0.0)

yarn add react-native-signature-canvas

or

npm install --save react-native-signature-canvas

This package depends on react-native-webview and it is particularly needed when you are using React Native CLI. To install react-native-webview follow the steps mentioned here

Installation(for React Native V0.5x.x or Expo SDK < v33)

npm install --save [email protected]

Usage

Basic

import Signature from "react-native-signature-canvas";

Custom

import SignatureScreen from "react-native-signature-canvas";

Properties

---

Prop	Type	Description
androidHardwareAccelerationDisabled	boolean	androidHardwareAccelerationDisabled for react-native-webview. Default is false
autoClear	boolean	should auto clear the signature after clicking the Confirm button
backgroundColor	string	default is "rgba(255,255,255,0)" (transparent), background color of the canvas
bgHeight	number	height of the background image
bgWidth	number	width of the background image
bgSrc	string	background image source uri (url)
clearText	string	clear button text
confirmText	string	save button text
customHtml	(injectedJavaScript: string) => string	html string that lets you modify things like the layout or elements
dataURL	string	default is "", Base64 string, draws saved signature from dataURL.
descriptionText	string	description text for signature
dotSize	number	radius of a single dot (not stroke width)
imageType	string	"image/png" (default), "image/jpeg"、"image/svg+xml", imageType of exported signature
minWidth	number	minimum width of a line. Defaults to 0.5
maxWidth	number	maximum width of a line. Defaults to 2.5
minDistance	number	Add the next point only if the previous one is farther than x pixels. Defaults to 5. 5
nestedScrollEnabled	boolean	enable nested scrolling for use inside of a scrollview
showsVerticalScrollIndicator	boolean	Boolean value that determines whether a vertical scroll indicator is shown in the WebView, The default value is true.
onOK	function	callback function after saving non-empty signature
onEmpty	function	callback function after trying to save an empty signature
onClear	function	callback function after clearing the signature
onGetData	function	callback function when getData() is called
onBegin	function	callback function when a new stroke is started
onEnd	function	callback function when the stroke has ended
onLoadEnd	function	callback function when the webview canvas load ended
onUndo	function	callback function when undo() is called
onRedo	function	callback function when redo() is called
onDraw	function	callback function when drawing is enabled
onErase	function	callback function when erasing is enabled
onChangePenColor	function	callback function after changing the pen color
onChangePenSize	function	callback function after changing the pen size
overlayHeight	number	height of the overlay image
overlayWidth	number	width of the overlay image
overlaySrc	string	overlay image source uri (url) must be .png with a transparent background
penColor	string	default is "black", color of pen
rotated	boolean	rotate signature pad 90 degrees
style	object	style of wrapper view
trimWhitespace	boolean	trim image whitespace
webStyle	string	webview style for overwrite default style, all style: https://github.com/YanYuanFE/react-native-signature-canvas/blob/master/h5/css/signature-pad.css
androidLayerType	none、software、hardware	Sets the android webview layerType

Methods

---

Function	Description
clearSignature()	Clear the current signature
changePenColor(color)	Change pen color
changePenSize(minW, maxW)	Change pen size
draw()	Enable drawing signature
erase()	Enable erasing signature
getData()	Triggers the onGetData callback with a single data JSON string
readSignature()	Reads the current signature on the canvas and triggers either the onOK or onEmpty callbacks
undo()	Undo last stroke
redo()	Redo last stroke

To call the methods use the useRef hook:

import SignatureScreen from "react-native-signature-canvas";

const Sign = ({ text, onOK }) => {
  const ref = useRef();

  // Called after ref.current.readSignature() reads a non-empty base64 string
  const handleOK = (signature) => {
    console.log(signature);
    onOK(signature); // Callback from Component props
  };

  // Called after ref.current.readSignature() reads an empty string
  const handleEmpty = () => {
    console.log("Empty");
  };

  // Called after ref.current.clearSignature()
  const handleClear = () => {
    console.log("clear success!");
  };

  // Called after end of stroke
  const handleEnd = () => {
    ref.current.readSignature();
  };

  // Called after ref.current.getData()
  const handleData = (data) => {
    console.log(data);
  };

  return (
    <SignatureScreen
      ref={ref}
      onEnd={handleEnd}
      onOK={handleOK}
      onEmpty={handleEmpty}
      onClear={handleClear}
      onGetData={handleData}
      autoClear={true}
      descriptionText={text}
    />
  );
};

export default Sign;

Using a background image

You can use a non-erasable background image to draw your signature on using the bgSrc prop. Make sure to provide the width and height of the image.

const imgWidth = 300;
const imgHeight = 200;
const style = `.m-signature-pad {box-shadow: none; border: none; }
              .m-signature-pad--body {border: none;}
              .m-signature-pad--footer {display: none; margin: 0px;}
              body,html {
              width: ${imgWidth}px; height: ${imgHeight}px;}`;
...
<View style={{ width: imgWidth, height: imgHeight }}>
  <SignatureScreen
    ref={ref}
    bgSrc="https://via.placeholder.com/300x200/ff726b"
    bgWidth={imgWidth}
    bgHeight={imgHeight}
    webStyle={style}
    onOK={handleOK}
  />
</View>

Using an overlay image

An overlay is a non-erasable image that can be used as a guideline similar to a colouring book. Make sure the image format is .png and that it has a transparent background. Also, don't forget to provide the width and height of the image. Use the overlaySrc prop to provide the link.

const imgWidth = 256;
const imgHeight = 256;
const style = `.m-signature-pad {box-shadow: none; border: none; }
              .m-signature-pad--body {border: none;}
              .m-signature-pad--footer {display: none; margin: 0px;}
              body,html {
              width: ${imgWidth}px; height: ${imgHeight}px;}`;
...
<View style={{ width: imgWidth, height: imgHeight }}>
  <SignatureScreen
    ref={ref}
    overlaySrc="http://pngimg.com/uploads/circle/circle_PNG63.png"
    overlayWidth={imgWidth}
    overlayHeight={imgHeight}
    webStyle={style}
    onOK={handleOK}
  />
</View>

Save Base64 Image as File

If you're using expo, you can use expo-file-system to save the base64 image as a local file; if you're working with react-native-cli, use react-native-fs.

import * as FileSystem from "expo-file-system";

const handleOK = (signature) => {
  const path = FileSystem.cacheDirectory + "sign.png";
  FileSystem.writeAsStringAsync(
    path,
    signature.replace("data:image/png;base64,", ""),
    { encoding: FileSystem.EncodingType.Base64 }
  )
    .then(() => FileSystem.getInfoAsync(path))
    .then(console.log)
    .catch(console.error);
};

Basic parameters

<Signature
  // handle when you click save button
  onOK={(img) => console.log(img)}
  onEmpty={() => console.log("empty")}
  // description text for signature
  descriptionText="Sign"
  // clear button text
  clearText="Clear"
  // save button text
  confirmText="Save"
  // String, webview style for overwrite default style, all style: https://github.com/YanYuanFE/react-native-signature-canvas/blob/master/h5/css/signature-pad.css
  webStyle={`.m-signature-pad--footer
    .button {
      background-color: red;
      color: #FFF;
    }`}
  autoClear={true}
  imageType={"image/svg+xml"}
/>

If you create your own triggers for the readSignature and/or clearSignature you can hide the built in Clear and Save buttons with css styles passed into the webStyle property.

const webStyle = `.m-signature-pad--footer
    .save {
        display: none;
    }
    .clear {
        display: none;
    }
`;
...
  <Signature
    webStyle={webStyle}
    onOK={handleOK}
    onEmpty={handleEmpty}
    onEnd={handleEnd}
  />

Custom Button for Confirm and Clear

import React, { useRef } from "react";
import { StyleSheet, View, Button } from "react-native";
import SignatureScreen from "react-native-signature-canvas";

const Sign = ({ onOK }) => {
  const ref = useRef();

  const handleOK = (signature) => {
    console.log(signature);
    onOK(signature);
  };

  const handleClear = () => {
    ref.current.clearSignature();
  };

  const handleConfirm = () => {
    console.log("end");
    ref.current.readSignature();
  };

  const style = `.m-signature-pad--footer {display: none; margin: 0px;}`;

  return (
    <View style={styles.container}>
      <SignatureScreen ref={ref} onOK={handleOK} webStyle={style} />
      <View style={styles.row}>
        <Button title="Clear" onPress={handleClear} />
        <Button title="Confirm" onPress={handleConfirm} />
      </View>
    </View>
  );
};

export default Sign;

const styles = StyleSheet.create({
  container: {
    flex: 1,
    alignItems: "center",
    justifyContent: "center",
    height: 250,
    padding: 10,
  },
  row: {
    display: "flex",
    flexDirection: "row",
    justifyContent: "space-between",
    width: "100%",
    alignItems: "center",
  },
});

Example

• Android
  

• iOS
  

import React, { useState } from "react";
import { StyleSheet, Text, View, Image } from "react-native";
import Signature from "react-native-signature-canvas";

export const SignatureScreen = () => {
  const [signature, setSign] = useState(null);

  const handleOK = (signature) => {
    console.log(signature);
    setSign(signature);
  };

  const handleEmpty = () => {
    console.log("Empty");
  };

  const style = `.m-signature-pad--footer
    .button {
      background-color: red;
      color: #FFF;
    }`;
  return (
    <View style={{ flex: 1 }}>
      <View style={styles.preview}>
        {signature ? (
          <Image
            resizeMode={"contain"}
            style={{ width: 335, height: 114 }}
            source={{ uri: signature }}
          />
        ) : null}
      </View>
      <Signature
        onOK={handleOK}
        onEmpty={handleEmpty}
        descriptionText="Sign"
        clearText="Clear"
        confirmText="Save"
        webStyle={style}
      />
    </View>
  );
};

const styles = StyleSheet.create({
  preview: {
    width: 335,
    height: 114,
    backgroundColor: "#F8F8F8",
    justifyContent: "center",
    alignItems: "center",
    marginTop: 15,
  },
  previewText: {
    color: "#FFF",
    fontSize: 14,
    height: 40,
    lineHeight: 40,
    paddingLeft: 10,
    paddingRight: 10,
    backgroundColor: "#69B2FF",
    width: 120,
    textAlign: "center",
    marginTop: 10,
  },
});

Using Typescript

To use Typescript just import SignatureViewRef and in useRef hook inform that the reference is of the SignatureViewRef type, with that the regular ref methods will be available.

import React, { useRef } from "react";
import SignatureScreen, {
  SignatureViewRef,
} from "react-native-signature-canvas";

interface Props {
  text: string;
  onOK: (signature) => void;
}

const Sign: React.FC<Props> = ({ text, onOK }) => {
  const ref = useRef<SignatureViewRef>(null);

  const handleSignature = (signature) => {
    console.log(signature);
    onOK(signature);
  };

  const handleEmpty = () => {
    console.log("Empty");
  };

  const handleClear = () => {
    console.log("clear success!");
  };

  const handleEnd = () => {
    ref.current?.readSignature();
  };

  return (
    <SignatureScreen
      ref={ref}
      onEnd={handleEnd}
      onOK={handleSignature}
      onEmpty={handleEmpty}
      onClear={handleClear}
      autoClear={true}
      descriptionText={text}
    />
  );
};

export default Sign;

Example inside ScrollView

When using react-native-signature-canvas inside a ScrollView, you will only get a point on the canvas and the ScrollView will handle the gesture making it unused for the canvas. The work around is to use the scrollEnabled prop of ScrollView. Here an example:

import React, {useState} from 'react';
import {ScrollView, View} from 'react-native';
import Signature from 'react-native-signature-canvas';

const SignInScroll = () => {
  const [scrollEnabled, setScrollEnabled] = useState(true);

  return (
    <ScrollView scrollEnabled={scrollEnabled}>
      <View style={{height: 300}}>
        <Signature
          onOK={(img) => console.log(img)}
          onBegin={() => setScrollEnabled(false)}
          onEnd={() => setScrollEnabled(true)}
          descriptionText="Sign"
          clearText="Clear"
          confirmText="Save"
          imageType="image/jpeg"
        />
      </View>
    </ScrollView>
  );
};

export default SignInScroll;