飞镖：取消发布延迟/将来 [英] Dart: cancelable post delay / future

问题描述

我是扑朔迷离的新手，我想通过调用API从 InputField 转换一些文本。但是，我不想在每个按键时都调用它，而只是在用户暂停键入时才调用它。

I am new to flutter and I want to translate some text from an InputField by calling an API. However I don't want to call it on every key stroke, but instead only when the user paused typing.

在Android上，我只会使用 Handler 类，该类具有 postDelay（），并预先调用 removeAllCallbacksAndMessages（null）。有没有办法在Dart上做类似的事情？

On Android I would just use the Handler class with postDelay() with beforehand calling removeAllCallbacksAndMessages(null). Is there a way to do something similar on Dart?

这是我当前的代码：

Future<String> getTranslation(String query, Language from, Language to) async {
    // cancel here if a call to this function was less than 500 millis ago.
    return Future.delayed(const Duration(milliseconds: 500), () {
      return _translator.translate(query, from: from.code, to: to.code)
    });
  }

编辑1

我像这样从Bloc调用代码：

I'm calling the code from my Bloc like so:

@override
  Stream<State> mapEventToState(Event event) async* {
    if (event is QueryChangeEvent) {
      yield TextTranslationChangeState(
          query: event.query ?? "",
          translation: await _repo.getTranslation(event.query, currentState.fromLang, currentState.toLang));
  }

这就是为什么我不能调用 .then（）的原因将来，因为我将无法从嵌套函数的块中产生新状态。

This is why I cannot call .then() on the future because I wouldn't be able to yield the new state from the block of the nested function.

任何帮助将不胜感激！

Any help is appreciated!

推荐答案

您可以使用<$来取消 Future 异步操作c $ c> CancelableOperation 。

You can achieve cancelling the Future async operation by using CancelableOperation.

这里是一个示例（ps我简化了方法签名，以便于我轻松测试）

Here is an example (p.s I simplified your method signature for me to test it easily)

  CancelableOperation cancellableOperation;

  Future<dynamic> fromCancelable(Future<dynamic> future) async {
    cancellableOperation?.cancel();
    cancellableOperation = CancelableOperation.fromFuture(future, onCancel: () {
      print('Operation Cancelled');
    });
    return cancellableOperation.value;
  }

  Future<dynamic> getTranslation(String query, String from, String to) async {
    return Future.delayed(const Duration(milliseconds: 1000), () {
      return "Hello";
    });
  }

在文本更改监听器上：

  onTextChanged() {
    fromCancelable(getTranslation("query", "EN", "TR")).then((value) {
      print("Then called: $value");
    });
  }

样本输出：

I/flutter ( 7312): Operation Cancelled
I/flutter ( 7312): Operation Cancelled
I/flutter ( 7312): Operation Cancelled
I/flutter ( 7312): Operation Cancelled
I/flutter ( 7312): Then called: Hello

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