uniapp中使用原生canvas标签绘制视频帧来模拟拍照，拍照后将图绘制在另外一个canvas上编辑画图，这样反复操作会导致ios系统上白屏，canvas2d上下文为null,经查阅找到相关资料
IOS 创建Canvas过多导致getContext(‘2d’) 返回null
总 Canvas 内存使用超过最大限制 (Safari 12)
从一个 bug 中延伸出 canvas 最大内存限制和浏览器渲染原理
可以提供一些启发解决思路，最终在项目中这样解决的

beforeDestroy() {this.timer && clearInterval(this.timer);this.closeCamera()this.video = nullif(this.canvas){this.canvas.width = 0this.canvas.height = 0this.canvas = nullthis.canvas2d = null}if(this.cameraCanvas){this.cameraCanvas.width = 0this.cameraCanvas.height = 0this.cameraCanvas = nullthis.cameraCanvas2d = null}
},

项目中还用了fabricjs，同样需要

fabricCanvasDispose() {console.log('释放内存')if (this.fabricCanvas) {let el = this.fabricCanvas.getElement()this.fabricCanvas.dispose();el.remove()this.fabricCanvas = null;}if (this.canvas) {this.canvas.width = 0this.canvas.height = 0this.canvas = null;this.canvas2d = null;}
}