React Native canvas in WebView
Question
I'm trying to code a "paint" Android app with React Native 0.17.
I have a Canvas component (strongly inspired by react-native-canvas ):
import React from 'react-native';
import Paint from '../utils/paint'
var {
View,
WebView
} = React;
const Canvas = React.createClass({
render() {
return (
<WebView
html={Paint}
style={this.props.style}
javaScriptEnabledAndroid={true}
/>
);
},
});
export default Canvas;
and a Paint component that I use in the html props of the WebView in the Canvas component above.
This component is nothing more than a very long string containing HTML and JS that come from this tuto: creating-a-paint-application-with-html5-canvas
export default `<html>
<head></head>
<body>
<h1 id='toto'>TATA</h1>
<br />
<div id="sketch">
<canvas id="paint" style='border: 1px solid black'></canvas>
</div>
<script>
(function() {
var canvas = document.querySelector('#paint');
var ctx = canvas.getContext('2d');
var sketch = document.querySelector('#sketch');
var sketch_style = getComputedStyle(sketch);
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));
var mouse = {x: 0, y: 0};
var start_events = ["mousedown", "touchstart"];
var move_events = ["mousemove", "touchmove"];
var end_events = ["mouseup", "touchend"];
/* Mouse Capturing Work */
move_events.forEach(function(event) {
canvas.addEventListener(event, function(e) {
mouse.x = e.pageX - this.offsetLeft;
mouse.y = e.pageY - this.offsetTop;
}, false);
});
/* Drawing on Paint App */
ctx.lineWidth = 5;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = 'back';
start_events.forEach(function(event) {
canvas.addEventListener(event, function(e) {
ctx.beginPath();
ctx.moveTo(mouse.x, mouse.y);
move_events.forEach(function(me){ canvas.addEventListener(me, onPaint, false); });
}, false);
});
end_events.forEach(function(event) {
canvas.addEventListener(event, function(e) {
move_events.forEach(function(me){ canvas.removeEventListener(me, onPaint, false); });
}, false);
});
var onPaint = function() {
ctx.lineTo(mouse.x, mouse.y);
ctx.stroke();
};
}());
</script>
</body>
</html>`;
My HTML/JS works well in a brower (Chrome) but unfortunately I'm not able to draw anything in my React Native app.
Can someone help me? Which events should I listen in React Native?
3 answers
solution1
4 ACCPTED 2015-12-22 13:29:11
ES6 template string seems to break when you comment some lines of JS in your <script> tag.
Try remove them:
export default `<html>
<head></head>
<body>
<h1 id='toto'>TATA</h1>
<br />
<div id="sketch">
<canvas id="paint" style='border: 1px solid black'></canvas>
</div>
<script>
(function() {
var canvas = document.querySelector('#paint');
var ctx = canvas.getContext('2d');
var sketch = document.querySelector('#sketch');
var sketch_style = getComputedStyle(sketch);
canvas.width = parseInt(sketch_style.getPropertyValue('width'));
canvas.height = parseInt(sketch_style.getPropertyValue('height'));
var mouse = {x: 0, y: 0};
var start_events = ["mousedown", "touchstart"];
var move_events = ["mousemove", "touchmove"];
var end_events = ["mouseup", "touchend"];
move_events.forEach(function(event) {
canvas.addEventListener(event, function(e) {
mouse.x = e.pageX - this.offsetLeft;
mouse.y = e.pageY - this.offsetTop;
}, false);
});
ctx.lineWidth = 5;
ctx.lineJoin = 'round';
ctx.lineCap = 'round';
ctx.strokeStyle = 'back';
start_events.forEach(function(event) {
canvas.addEventListener(event, function(e) {
ctx.beginPath();
ctx.moveTo(mouse.x, mouse.y);
move_events.forEach(function(me){ canvas.addEventListener(me, onPaint, false); });
}, false);
});
end_events.forEach(function(event) {
canvas.addEventListener(event, function(e) {
move_events.forEach(function(me){ canvas.removeEventListener(me, onPaint, false); });
}, false);
});
var onPaint = function() {
ctx.lineTo(mouse.x, mouse.y);
ctx.stroke();
};
}());
</script>
</body>
</html>`;
solution2
2 2018-11-18 21:04:16
react-native-canvas current maintainer here, to people coming here looking for a canvas solution for React Native: I want to let you know react-native-canvas today is a stable solution which is very different from the code injection hack it used to be.
solution3
0 2020-12-23 23:57:32
@flyskywhy/react-native-gcanvas is a C++ native canvas component based on gpu opengl glsl shader, runs well on Android and iOS. You can see Performance Test Result , and an easily <canvas/> ported example react-native-particles-bg runs on Android, iOS and Web.
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