因为View不可见，所以直接调用转换 bitmap 的方法不可行，必须得先把View 绘制出来再去转换。

项目中使用的是ScrollView，所以绘制的方法如下：

val scrollView = view.findViewById<ScrollView>(R.id.scrollView)
scrollView.measure(
                View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED),
                View.MeasureSpec.makeMeasureSpec(0,View.MeasureSpec.UNSPECIFIED)
)
scrollView.layout(0,0,scrollView.measuredWidth,scrollView.measuredHeight)

然后再调用 ScrollView 的截图方法即可：

public static Bitmap snapshotByScrollView(final ScrollView scrollView, final Bitmap.Config config) {
        if (scrollView == null || config == null) return null;
        try {
            View view = scrollView.getChildAt(0);
            int width = view.getWidth();
            int height = view.getHeight();

            Bitmap bitmap = Bitmap.createBitmap(width, height, config);
            Canvas canvas = new Canvas(bitmap);
            canvas.drawColor(BACKGROUND_COLOR);
            scrollView.layout(0, 0, scrollView.getMeasuredWidth(),
                    scrollView.getMeasuredHeight());
            scrollView.draw(canvas);
            return bitmap;
        } catch (Exception e) {
            Log.i(TAG, "snapshotByScrollView exception:${e}");
        }
        return null;
    }