Question

我希望暂停执行我的Dart脚本（在网页中），直到用户点击密钥为止。以下代码有效，但我想知道是否有更好的方法：

import 'dart:html';
import 'dart:async';

StreamSubscription sub;

Future main() async {
  KeyboardEvent k = await getkey();
  print(k.keyCode.toString());
}

Future<KeyboardEvent> getkey() async {
  Completer<KeyboardEvent> c = new Completer<KeyboardEvent>();
  sub = document.onKeyDown.listen((KeyboardEvent e){
    sub.cancel();
    c.complete(e);
  });
  return c.future;
}

更新：Gunter的解决方案非常理想。上面的代码缩短为：

import 'dart:html';
import 'dart:async';

StreamSubscription sub;

Future main() async {
  KeyboardEvent k = await getkey();
  print(k.keyCode.toString());
}

Future<KeyboardEvent> getkey() async {
  return document.onKeyDown.first;
}

但是，如果我想过滤按键，我想我会回到以前的风格：

import 'dart:html';
import 'dart:async';

StreamSubscription sub;

Future main() async {
  KeyboardEvent k = await getkey([KeyCode.A,KeyCode.B,KeyCode.C,KeyCode.D]);
  print(k.keyCode.toString());
}

Future<KeyboardEvent> getkey([List<int> lst]) async {
  Completer<KeyboardEvent> c = new Completer<KeyboardEvent>();
  sub = document.onKeyDown.listen((KeyboardEvent e){
    if ((lst==null)||(lst.contains(e.keyCode))){
      sub.cancel();
      c.complete(e);
    }
  });
  return c.future;
}

是吗？

更新再次感谢Gunter！结果是：

Future<KeyboardEvent> getkey([List<int> lst]) async {
  return document.onKeyDown.firstWhere((KeyboardEvent e)=>((lst==null)||(lst.contains(e.keyCode))));
}

使用如下：

import 'dart:html';
import 'dart:async';

Future main() async {
  KeyboardEvent k = await getkey();
  print(k.keyCode.toString());
  KeyboardEvent k = await getkey([KeyCode.A,KeyCode.B,KeyCode.C,KeyCode.D]);
  print(k.keyCode.toString());
}

Answer 1

未经测试，但据我记得更改

  Completer<KeyboardEvent> c = new Completer<KeyboardEvent>();
  sub = document.onKeyDown.listen((KeyboardEvent e){
    sub.cancel();
    c.complete(e);
  });
  return c.future;

到

  return document.onKeyDown.first;

也应该这样做。

更新

  return document.onKeyDown.firstWhere((KeyboardEvent e) => 1st.contains(e.keyCode));

（再次未经测试）

在Dart等待按键

1 个答案:

更新