flutter - Widget get _appBar 在 flutter 中的含义是什么

Question

我正在阅读这样的 flutter 代码:

  Widget get _appBar {
    return Column(
      children: <Widget>[
        Container(
          decoration: BoxDecoration(
            gradient: LinearGradient(
              colors: [Color(0x66000000), Colors.transparent],
              begin: Alignment.topCenter,
              end: Alignment.bottomCenter,
            ),
          ),
          child: Container(
            padding: EdgeInsets.fromLTRB(14, 20, 0, 0),
            height: 86.0,
            decoration: BoxDecoration(
                color:
                    Color.fromARGB((appBarAlpha * 255).toInt(), 255, 255, 255),
                boxShadow: [
                  BoxShadow(
                    color: appBarAlpha == 1.0
                        ? Colors.black12
                        : Colors.transparent,
                    offset: Offset(2, 3),
                    blurRadius: 6,
                    spreadRadius: 0.6,
                  ),
                ]),
            child: SearchBar(
              searchBarType: appBarAlpha > 0.2
                  ? SearchBarType.homeLight
                  : SearchBarType.home,
              inputBoxClick: _jumpToSearch,
              defaultText: SEARCH_BAR_DEFAULT_TEXT,
              leftButtonClick: () {},
              speakClick: _jumpToSpeak,
              rightButtonClick: _jumpToUser,
            ),
          ),
        ),
        Container(
            height: appBarAlpha > 0.2 ? 0.5 : 0,
            decoration: BoxDecoration(
                boxShadow: [BoxShadow(color: Colors.black12, blurRadius: 0.5)]))
      ],
    );
  }

Widget get _appBar是什么意思？它有一个 appBar 控件吗？为什么不直接返回一个 AppBar？

Answer 1

它是一个“getter”:

Getters and setters are special methods that provide read and write access to an object’s properties. Recall that each instance variable has an implicit getter, plus a setter if appropriate. You can create additional properties by implementing getters and setters, using the get and set keywords

( Dart Documentation )

所以 Widget get _appBar 是 _appBar 类型的 Widget 属性的 getter。您可以将其设为函数:Widget _appBar()。

我猜你的代码在多个地方使用了这个应用程序栏，所以找到了一种方法将代码放在一个地方以从所有其他地方调用它而不是复制所有代码。