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react-native-signature-canvas

npm GitHub last commit runs with expo

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

  • Supports Android and iOS and Expo
  • Pure JavaScript implementation with no native dependencies
  • Tested with RN 0.50
  • Core use signature_pad.js
  • Only depend on react and react native
  • 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

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

npm install --save react-native-signature-canvas@1.4.2

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 function 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
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
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

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;