flutter报错：NoSuchMethodError: The method '>' was called on null.

写了个list,发现出不来，报错

flutter: Another exception was thrown: RenderBox was not laid out: _RenderScrollSemantics#81b3a relayoutBoundary=up3 NEEDS-PAINT
flutter: Another exception was thrown: 'package:flutter/src/rendering/shifted_box.dart': Failed assertion: line 314 pos 12: 'child.hasSize': is not true.
flutter: Another exception was thrown: NoSuchMethodError: The method '<=' was called on null.
flutter: Another exception was thrown: NoSuchMethodError: The getter 'visible' was called on null.

搜了搜发现是Column或Row里面要加个Flexible来包裹里面的内容： https://github.com/flutter/flutter/issues/21628

Column(
    children: <Widget>[
        Flexible(
           child: ListView(
              children: <Widget>[
                 ListTitle(leading:Icon(Icons.code),title:Text('hahaha'))
              ],
           ),
        )
    ],
)

解决了，但不知道具体是为何