在 Canvas 上反应 useRef 得到 null 或 undefined

Question

I am trying to reference a canvas DOM element to make the width of it the same as its parent without messing with the scale of the canvas. When doing so I am getting a Uncaught TypeError: _canvasRef$current.getContext is not a function error and am not exactly sure how to fix it.

Ive console logged a few things just to make the app run but the issue is within the useEffect

import SignaturePad from 'react-signature-canvas'

const canvasRef = useRef<HTMLCanvasElement>(null)

useEffect(() => {
    const ctx: CanvasRenderingContext2D | null | undefined =
        canvasRef.current?.getContext('2d')
    const ctxContainer = document.getElementById('ctxContainer')

    console.log('ctx: ', ctx)
    // if (ctx && ctxContainer) {
    //     ctx.style.width = '100%'
    //     ctx.style.height = '100%'
    //     ctx.width = ctxContainer.clientWidth
    // }
}, [])

const save = () => {
    console.log('saved!')
}

console.log('canvasRef: ', canvasRef)

return (
    <div id={`ctxContainer`} className={'signatureInput__option-draw'}>
        <SignaturePad
            ref={canvasRef}
            canvasProps={{
                className: 'signatureInput__option-draw__canvas',
            }}
            onEnd={save}
        />
    </div>
)

Answer 1

Try this.

Note that you may still need to do some changes to following code to full fill your full requirement ( such as event handling when the user change the screen sizes. ) The following code will fix the issue you are facing right now.

  useEffect(() => {
    if (canvasRef.current) {
      const canvas = canvasRef.current.getCanvas();
      const ctx = canvas.getContext('2d');

      // do something with the canvas ref
      if (ctx) {
        ctx.canvas.width = window.innerHeight;
        ctx.canvas.height = window.innerHeight;
      }
    }
  }, []);

Answer 2

Try using getCanvas() . i dont think getContext() is provided with the package

function App() {
  const canvasRef = React.createRef(null);

  useEffect(() => {
    const canvas = canvasRef.current;
    console.log(canvas.current);
    const ctx = canvas.getCanvas();
    const ctxContainer = document.getElementById("ctxContainer");

    console.log("ctx: ", ctx);
    if (ctx && ctxContainer) {
      ctx.style.width = "100%";
      ctx.style.height = "100%";
      ctx.width = ctxContainer.clientWidth;
    }
  }, []);

  const save = () => {
    console.log("saved!");
  };

  console.log("canvasRef: ", canvasRef);

  return (
    <div className="App">
      <div id={`ctxContainer`} className={"signatureInput__option-draw"}>
        <SignaturePad
          ref={(ref) => {
            canvasRef.current = ref;
          }}
          canvasProps={{
            className: "signatureInput__option-draw__canvas",
          }}
          onEnd={save}
        />
      </div>
    </div>
  );
}