我在unbindDrawables中收到空指针异常,我正在删除所有背景可绘制对象上的回调。protectedvoidonDestroy(){super.onDestroy();unbindDrawables(findViewById(R.id.top_layout));Runtime.getRuntime().gc();}privatevoidunbindDrawables(Viewview){if(view.getBackground()!=null){view.getBackground().setCallback(null);}if(viewinstanceofViewGroup