异步正在向调用者滚雪球，不能使构造函数异步 [英] async is snowballing to callers, can't make constructor async
问题描述
我有一个函数 loadData ，它可以从文件中加载一些文本:
I have a function loadData that loads some text from a file:
Future<String> loadAsset() async {
return await rootBundle.loadString('assets/data/entities.json');
}
loadString 方法来自Flutter SDK，并且是异步的.
The loadString method is from Flutter SDK, and is asynchronous.
然后在另一个方法中调用 loadAsset 方法，该方法必须标记为 async ，因为 loadAsset 是异步的，我需要使用等待:
The loadAsset method is then called in another method, that must me marked as async, since loadAsset is async and I need to use await:
Future<List<Entity>> loadEntities() async {
String jsonData = await loadAsset();
return parseData(jsonData);
}
parseData 方法不是异步的，它接收一个 String ，对其进行解析，并返回一个对象列表:
The parseData method is not async, it receives a String, parse it, and return a list of objects:
List<Entity> parseData(String jsonString) {
...
}
但是由于 loadEntities 必须标记为 async ，因此这要求它返回 Future ，但是实际上，它不是> Future ，因为自从我使用 await 以来，它将等待 loadAsset 方法完成，然后使用结果调用 parseData 函数
But since loadEntities must be marked with async, this requires that it returns a Future, but in practice, it's not a Future because since I use await, it awaits for the loadAsset method to finish, then call the parseData funcion using the result.
这很容易变成 async 调用的滚雪球，因为每个使用 loadEntities 的方法也都必须标记为 async .
This easily turns into a snowball of async call, because every method that uses loadEntities must be marked as async too.
此外，我不能在类构造函数中使用 loadEntities ，因为该构造函数应标记为 async ，这在Dart中是不允许的.
Also, I can't use loadEntities in a class constructor, because the constructor should be marked as async, which is not allowed in Dart.
我在Dart中使用 async/await 模式错误吗?如何在类构造函数中使用 loadEntities 方法?
Am I using the async/await pattern in Dart wrong? How could I use the loadEntities method in a class constructor?
推荐答案
不，异步具有传染性，无法从异步返回同步执行.
No, async is contagious and there is no way to go back from async to sync execution.
async / await 仅是 methodThatReturnsFuture().then(...)
使用 async 标记方法只是为了允许您在其主体内部使用 await .如果没有 async ，您仍然需要返回 Future ，以便调用代码仅在 loadAsset()的结果可用后才能执行.
Marking a method with async is only to allow you to use await inside its body. Without async you would still need to return a Future for calling code to only execute after the result of loadAsset() becomes available.
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