Dart 将方法作为参数传递给小部件_Dart_Flutter

Dart 将方法作为参数传递给小部件

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Dart 将方法作为参数传递给小部件,dart,flutter,Dart,Flutter,我有一个自定义按钮小部件： class Button extends StatelessWidget { final String text; Button(this.text); @override Widget build(BuildContext context) { return Container( height: 50, child: SizedBox( width: double.infinity,

我有一个自定义按钮小部件：

class Button extends StatelessWidget {
  final String text;

  Button(this.text);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: () => {}, // Use the function from parent Widget
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

...
myMethod () => {
   // do some stuff
}
...
Padding(
    padding: EdgeInsets.only(bottom: 10),
    child: Button("Log in", myMethod),
),
...

然后在父窗口小部件中，我想将一个

onPressed

方法传递给这个按钮小部件：

class Button extends StatelessWidget {
  final String text;

  Button(this.text);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: () => {}, // Use the function from parent Widget
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

...
myMethod () => {
   // do some stuff
}
...
Padding(
    padding: EdgeInsets.only(bottom: 10),
    child: Button("Log in", myMethod),
),
...

如何告诉按钮小部件使用

myMethod

进行

onPress

？

使用

VoidCallback

类型，如下所示：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

已经存在一些预定义类型

无效回调如果要创建类似以下内容的参数：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

然后您可以在类中定义它，如下所示：

类MyWidget扩展了无状态Widget{
MyWidget（{Key-Key，this.onPressed}）：超级（Key:Key）；
最后一次按下按钮；
// ...
}

笔记

typedef

在源代码中定义如下：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

异步版本是

AsyncCallback

typedef AsyncCallback = Future<void> Function();

然后您可以在类中定义它，如下所示：

类MyWidget扩展了无状态Widget{
MyWidget（{Key-Key，this.onPressed}）：超级（Key:Key）；
终值设定人；
// ...
}

笔记 typedef在源代码中定义如下：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

估价师如果要创建类似以下内容的参数：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

然后您可以在类中定义它，如下所示：

类MyWidget扩展了无状态Widget{
MyWidget（{Key-Key，this.onPressed}）：超级（Key:Key）；
最终估价师已按下；
// ...
}

笔记 typedef在源代码中定义如下：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

定义您自己的类型从上面的所有示例中可以看出，对于

函数

，一切都只是

typedef

。所以你很容易就能做出自己的决定

假设你想做这样的事情：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

然后您将使typedef如下所示：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

然后像这样使用它：

class Button extends StatelessWidget {
  final String text;
  final VoidCallback callback;

  Button(this.text, this.callback);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 50,
      child: SizedBox(
        width: double.infinity,
        child: RaisedButton(
          onPressed: callback, // Simply put the function name here, DON'T use ()
          child: Padding(
              padding: EdgeInsets.symmetric(vertical: 13),
              child: Text(
                text,
                style: TextStyle(fontWeight: FontWeight.bold),
              )),
          color: COLOR_BLUE,
          textColor: Colors.white,
          shape:
              RoundedRectangleBorder(borderRadius: BorderRadius.circular(25)),
        ),
      ),
    );
  }
}

onPressed: () { },

typedef VoidCallback = void Function();

onPressed: (value) { },

typedef ValueSetter<T> = void Function(T value);

onPressed: () => value,

typedef ValueGetter<T> = T Function();

onEvent: (context, child) => value,

typedef MyEventCallback = int Function(BuildContext context, Widget widget);

类MyWidget扩展了无状态Widget{
MyWidget（{Key-Key，this.onEvent}）：超级（Key:Key）；
最后一次MyEventCallback onEvent；
// ...
}

有关更多信息，请参阅。

查看a+1的操作方法。如果您想要一个接受参数和/或返回结果的方法，也可以为方法定义自己的typedef：比如我创建了一个返回TextField的CustomTextField。如何为onChanged属性创建构造函数并正确传递它？我试图为CustomTextField创建一个构造函数，将函数正确地传递给里面的TextField。事情就像一次改变：一次改变。@IvánYoed，你可以做同样的事情。他们的

值发生了变化？一旦更改

，其中

值更改

定义为

无效函数（T值）

。