如何在android上使用vue-nativescript更改画布上绘制的位图？

<template>
  <Page>
    <Canvas ref="canvas" @draw="onDraw" width="300" height="300" />
    <Button text="修改位图" @tap="changeBitmap" />
  </Page>
</template>

<script>
  import { isAndroid } from '@nativescript/core';

  export default {
    methods: {
      onDraw(args) {
        const canvas = args.object;
        const paint = new android.graphics.Paint();
        const bitmap = android.graphics.Bitmap.createBitmap(300, 300, android.graphics.Bitmap.Config.ARGB_8888);
        const canvas = new android.graphics.Canvas(bitmap);

        paint.setStyle(android.graphics.Paint.Style.FILL);
        paint.setColor(android.graphics.Color.BLUE);

        canvas.drawRect(0, 0, 300, 300, paint);

        const imageView = new android.widget.ImageView(isAndroid ? this.$refs.canvas.nativeView.getContext() : null);
        imageView.setImageBitmap(bitmap);
        this.$refs.canvas.nativeView.addView(imageView);
      },
      changeBitmap() {
        const imageView = this.$refs.canvas.nativeView.getChildAt(0);
        const bitmap = imageView.getDrawingCache();

        // 修改位图
        // TODO: 进行位图操作，例如修改像素颜色等

        imageView.setImageBitmap(bitmap);
      }
    }
  };
</script>