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Dart中的Typedefs

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Bram Vanbilsen · 技术社区 · 8 年前

因此,我在Dart中使用typedefs已经有一段时间了,但没有考虑它们实际上是什么。例如,在这段代码中:

new PageRouteBuilder(
  pageBuilder: (BuildContext context, Animation<double> animation1, Animation<double> animation2) => new Test(),
  transitionsBuilder: (BuildContext context, Animation<double> animation1, Animation<double> animation2, Widget child) {
    return new FadeTransition(
      child: child,
      opacity: animation1,
    );
  }
)

这个 pageBuilder 属性需要一个名为 RoutePageBuilder 对于 transitionsBuilder 属性调用了typedef RouteTransitionsBuilder 应为。

对我来说,看起来我只是在使用一个函数来处理那些属性,这些属性具有来自typedef的预定义参数,但我对此不确定。
还有,什么参数实际上是这里的输入?因为我举个例子 Animation<double> animation1 作为一个参数,但这实际上不会创建一个新的 Animation ,还是这样?如果没有,怎么办 动画 将实际作为参数传递?

2 回复 | 直到 8 年前

Antonino 8 年前

typedef可以用来指定我们想要的函数签名要匹配的特定功能。函数签名由函数的参数(包括其类型)。返回类型不是函数签名的一部分。其语法如下。

在您的情况下,PageRouteBuilder采用以下参数:

pageBuilder RoutePageBuilder typedef-只是一个与RoutePageBuilder typedef签名匹配的函数。
transitionsBuilder RouteTransitionsBuilder typedef-与pageBuilder完全相同,但与RouteTransitionsBuilder签名匹配。

这两个TypeDef(RouteTransitionsBuilder和RoutePageBuilder)类似于单一方法的接口(面向对象编程)。在这种情况下,typedef RoutePageBuilder强制您作为参数传递一个函数,该函数返回一个以上下文和两个动画为参数的小部件。

如果您想了解在该函数中传递的参数的更多详细信息,可以在颤振的文档中查看,例如:

动画动画驱动管线的过渡和上一条路线的前向过渡。只读,继承

或

secondaryAnimation动画管线的动画被推到这条路线的顶端。此动画允许此路线与推进路线的入口和出口过渡相协调这条路线的顶端。只读,继承

PS:如果你通过颤振代码导航并到达路线。dart文件您可以找到记录此零件的注释:

/// Override this method to build the primary content of this route.
  ///
  /// The arguments have the following meanings:
  ///
  ///  * `context`: The context in which the route is being built.
  ///  * [animation]: The animation for this route's transition. When entering,
  ///    the animation runs forward from 0.0 to 1.0. When exiting, this animation
  ///    runs backwards from 1.0 to 0.0.
  ///  * [secondaryAnimation]: The animation for the route being pushed on top of
  ///    this route. This animation lets this route coordinate with the entrance
  ///    and exit transition of routes pushed on top of this route.
  ///
  /// This method is called when the route is first built, and rarely
  /// thereafter. In particular, it is not called again when the route's state
  /// changes. For a builder that is called every time the route's state
  /// changes, consider [buildTransitions]. For widgets that change their
  /// behavior when the route's state changes, consider [ModalRoute.of] to
  /// obtain a reference to the route; this will cause the widget to be rebuilt
  /// each time the route changes state.
  ///
  /// In general, [buildPage] should be used to build the page contents, and
  /// [buildTransitions] for the widgets that change as the page is brought in
  /// and out of view. Avoid using [buildTransitions] for content that never
  /// changes; building such content once from [buildPage] is more efficient.
  Widget buildPage(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation);

Peter Haddad 7 年前

从 docs :

在Dart中,函数是对象,就像字符串和数字是对象一样。typedef或函数类型别名(也称为)为函数类型提供了一个名称,您可以在声明字段和返回类型时使用该名称。当函数类型分配给变量时,typedef保留类型信息。

示例,如果您检查 RoutePageBuilder :

typedef RoutePageBuilder = Widget Function(BuildContext context, Animation<double> animation, Animation<double> secondaryAnimation);

这意味着 RoutePageBuilder 也称为 Function 返回一个 Widget .

如果您检查 PageRouteBuilder ,您将发现实例变量 pageBuilder 属于类型 RoutePageBuilder ,因此在创建的新实例时 PageRouteBuilder 您可以执行以下操作:

new PageRouteBuilder(
  pageBuilder: (BuildContext context, Animation<double> animation1, Animation<double> animation2) => new Test(),

在这里 new Test() 是一个小部件。