Im trying to build an audio progess bar with react hooks. I was following a tutorial with react class based components but got a little lost with refs.
How can I give my useRef variables an initial value of the div ref when the page loads?
As soon as I start playing then the I get an error saying cant read offsetwidth of null. Obviously timeline ref is null as it doesnt have an initial value. How can I connect it to the div with id of timeline in the useEffect hook?
const AudioPlayer = () => {
const url = "audio file";
const [audio] = useState(new Audio(url));
const [duration, setDuration] = useState(0);
const [currentTime, setCurrentTime] = useState(0)
let timelineRef = useRef()
let handleRef = useRef()
useEffect(() => {
audio.addEventListener('timeupdate', e => {
setDuration(e.target.duration);
setCurrentTime(e.target.currentTime)
let ratio = audio.currentTime / audio.duration;
let position = timelineRef.offsetWidth * ratio;
positionHandle(position);
})
}, [audio, setCurrentTime, setDuration]);
const mouseMove = (e) => {
positionHandle(e.pageX);
audio.currentTime = (e.pageX / timelineRef.offsetWidth) * audio.duration;
};
const mouseDown = (e) => {
window.addEventListener('mousemove', mouseMove);
window.addEventListener('mouseup', mouseUp);
};
const mouseUp = (e) => {
window.removeEventListener('mousemove', mouseMove);
window.removeEventListener('mouseup', mouseUp);
};
const positionHandle = (position) => {
let timelineWidth = timelineRef.offsetWidth - handleRef.offsetWidth;
let handleLeft = position - timelineRef.offsetLeft;
if (handleLeft >= 0 && handleLeft <= timelineWidth) {
handleRef.style.marginLeft = handleLeft + "px";
}
if (handleLeft < 0) {
handleRef.style.marginLeft = "0px";
}
if (handleLeft > timelineWidth) {
handleRef.style.marginLeft = timelineWidth + "px";
}
};
return (
<div>
<div id="timeline" ref={(timeline) => { timelineRef = timeline }}>
<div id="handle" onMouseDown={mouseDown} ref={(handle) => { handleRef = handle }} />
</div>
</div>
)
}
The useRef()
hook returns a reference to an object, with the current
property. The current
property is the actual value useRef
points to.
To use the reference, just set it on the element:
<div id="timeline" ref={timelineRef}>
<div id="handle" onMouseDown={mouseDown} ref={handleRef} />
And then to use it, you need to refer to the current
property:
let position = current.timelineRef.offsetWidth * ratio;
And positionHandle
- you shouldn't actually set styles on elements in React in this way. Use the setState()
hook, and set the style using JSX.
const positionHandle = (position) => {
let timelineWidth = timelineRef.current.offsetWidth - handleRef.current.offsetWidth;
let handleLeft = position - timelineRef.current.offsetLeft;
if (handleLeft >= 0 && handleLeft <= timelineWidth) {
handleRef.current.style.marginLeft = handleLeft + "px";
}
if (handleLeft < 0) {
handleRef.current.style.marginLeft = "0px";
}
if (handleLeft > timelineWidth) {
handleRef.current.style.marginLeft = timelineWidth + "px";
}
};
In addition, the ref can be also used for other values, such as the new Audio(url)
, and be extracted from the current
property:
const { current: audio } = useRef(new Audio(url));