flutter - Flutter中调用方法的不同方式

Question

我想知道有什么区别：

onPressed: method

onPressed: method()

onPressed: () => method()

在FlutteronPressed中的 a 参数中。RaisedButton

标签： flutterdart

Answer 1

1. onPressed: myCall当 onPressed 属性动作发生时，这将触发方法 myCall。

2. onPressed: myCall()这是方法的调用

3. onPressed: ()=>mycall()这将创建一个匿名函数，该函数将方法 mycall()

4. RaisedButton 的 onPressed 参数只是一个类似于任何其他对象的字段。该字段不是原始的（即布尔值或整数），而是一个函数。您可能已经注意到，它是 RaisedButton 的必填字段。这意味着，如果不提供 onPressed 属性的值，您就无法创建 RaisedButton 的实例。下面是 RaisedButton 的构造函数的代码片段：

    class RaisedButton extends MaterialButton {
    /// Create a filled button.
    ///
    /// The [elevation], [highlightElevation], [disabledElevation], and
    /// [clipBehavior] arguments must not be null. Additionally,  [elevation],
    /// [highlightElevation], and [disabledElevation] must be non-negative.
    const RaisedButton({
    Key key,
    @required VoidCallback onPressed,
    ValueChanged<bool> onHighlightChanged,
    ButtonTextTheme textTheme,
    Color textColor,
    Color disabledTextColor,
    Color color,
    Color disabledColor,
    Color highlightColor,
    Color splashColor,
    Brightness colorBrightness,
    double elevation,
    double highlightElevation,
    double disabledElevation,
    EdgeInsetsGeometry padding,
    ShapeBorder shape,
    Clip clipBehavior = Clip.none,
    MaterialTapTargetSize materialTapTargetSize,
    Duration animationDuration,
    Widget child,
    }) : assert(elevation == null || elevation >= 0.0),
         assert(highlightElevation == null || highlightElevation >= 0.0),
         assert(disabledElevation == null || disabledElevation >= 0.0),
         super(
               key: key,
               onPressed: onPressed,
               onHighlightChanged: onHighlightChanged,
               textTheme: textTheme,
               textColor: textColor,
               disabledTextColor: disabledTextColor,
               color: color,
               disabledColor: disabledColor,
               highlightColor: highlightColor,
               splashColor: splashColor,
               colorBrightness: colorBrightness,
               elevation: elevation,
               highlightElevation: highlightElevation,
               disabledElevation: disabledElevation,
               padding: padding,
               shape: shape,
               clipBehavior: clipBehavior,
               materialTapTargetSize: materialTapTargetSize,
               animationDuration: animationDuration,
               child: child,
              );