flutter中引入高德地图报错【../../flutter/flutter/.pub-cache/hosted/pub.dartlang.org/amap_map_fluttify-2.0.2/lib/src/facade/amap_view.widget.dart:282:29: Error: Method 'addPostFrameCallback' cannot be called on 'WidgetsBinding?' because it is potentially null. - 'WidgetsBinding' is from 'package:flutter/src/widgets/binding.dart' ('../../flutter/flutter/packages/flutter/lib/src/widgets/binding.dart'). Try calling using ?. instead. WidgetsBinding.instance.addPostFrameCallback((duration) async { ^^^^^^^^^^^^^^^^^^^^】

这个报错是因为在Flutter 2.0及以上版本中，WidgetsBinding.instance被标记为可选参数，即可能为空。解决这个问题的方法是使用“?.”操作符代替“.”操作符调用WidgetsBinding实例中的方法。你可以在addPostFrameCallback方法前加上“WidgetsBinding.instance?”来解决这个问题，代码如下所示：

WidgetsBinding.instance?.addPostFrameCallback((duration) async {
  // your code here
});

这样可以避免WidgetsBinding实例为空时引发的异常。