Flutter - VoidCallback 内容未执行

Question

我创建了以下客户小部件：

class MainButtonWidget extends StatelessWidget{
  String _text = "";
  TextTheme _textTheme = new TextTheme();
  IconData _icon = null;
  VoidCallback _onPressed;

  MainButtonWidget(String text, TextTheme textTheme, IconData icon, VoidCallback onPressed){
    _text = text;
    _textTheme = textTheme;
    _icon = icon;
    _onPressed = onPressed;
  }

  void setText(String text){
    _text = text;
  }

@override
Widget build(BuildContext context) {
  return new Container(
    child: new RaisedButton(
      padding: const EdgeInsets.fromLTRB(
          Dimens.edgeMainButtonLRB, Dimens.edgeMainButtonT,
          Dimens.edgeMainButtonLRB, Dimens.edgeMainButtonLRB),
      shape: new CircleBorder(side: new BorderSide(
          color: ColorRes.whiteTranslucent2,
          width: Dimens.widthSmallButtonHome)),
      onPressed: (){
        debugPrint("mainButtonWidget before _onPressed");
        _onPressed;
        debugPrint("mainButtonWidget after _onPressed");
        },
      color: Colors.transparent,
      child: new Column(
        children: <Widget>[
          new Icon(
            _icon,
            color: Colors.white,
          ),
          new Text(_text,
            style: _textTheme.button.copyWith(
              color: Colors.white,
            ),)
        ],
      ),
    ),
  );
}

}

这是我如何创建 MainButtonWidget 类型的对象：

Widget mapMainBtn = new MainButtonWidget('Map', textTheme, Icons.location_on, ()=> debugPrint("mapMainBtn -> onPressed called"));

按下按钮时似乎 VoidCallback 的内容没有执行。

在日志中显示以下消息： I/flutter (21436)：_onPressed 之前的 mainButtonWidget I/flutter (21436)：_onPressed 后的 mainButtonWidget

我希望在上述消息之间看到“mapMainBtn -> onPressed called”。

Answer 1

_onPressed() 被调用。
请看下面的代码：

`onPressed: (){
 debugPrint("mainButtonWidget before _onPressed");
    _onPressed;
    debugPrint("mainButtonWidget after _onPressed");
}`

Answer 2

需要调用()

_onPressed();