Flutter学习笔记3-dart:async

一、需要引入依赖：

import 'dart:async';

二、Future

await

应该优先使用await，而不是直接使用Future API
使用Future：

runUsingFuture() {
  // ...
  findEntryPoint().then((entryPoint) {
    return runExecutable(entryPoint, args);
  }).then(flushThenExit);
}

使用await：

runUsingAsyncAwait() async {
  // ...
  var entryPoint = await findEntryPoint();
  var exitCode = await runExecutable(entryPoint, args);
  await flushThenExit(exitCode);
}

基本应用

HttpRequest.getString(url).then((String result) {
  print(result);
});

HttpRequest.getString(url).then((String result) {
  print(result);
}).catchError((e) {
  // Handle or ignore the error.
});

Future result = costlyQuery(url);
result
    .then((value) => expensiveWork(value))
    .then((_) => lengthyComputation())
    .then((_) => print('Done!'))
    .catchError((exception) {
  /* Handle exception... */
});

Future deleteLotsOfFiles() async =>  ...
Future copyLotsOfFiles() async =>  ...
Future checksumLotsOfOtherFiles() async =>  ...

await Future.wait([
  deleteLotsOfFiles(),
  copyLotsOfFiles(),
  checksumLotsOfOtherFiles(),
]);
print('Done with all the long steps!');

三、Stream

使用Stream：

void main(List<String> arguments) {
  // ...
  FileSystemEntity.isDirectory(searchPath).then((isDir) {
    if (isDir) {
      final startingDir = Directory(searchPath);
      startingDir
          .list(
              recursive: argResults[recursive],
              followLinks: argResults[followLinks])
          .listen((entity) { //使用stream的listen()方法来订阅文件列表
        if (entity is File) {
          searchFile(entity, searchTerms);
        }
      });
    } else {
      searchFile(File(searchPath), searchTerms);
    }
  });
}

使用await for

Future main(List<String> arguments) async {
  // ...
  if (await FileSystemEntity.isDirectory(searchPath)) {
    final startingDir = Directory(searchPath);
    await for (var entity in startingDir.list(
        recursive: argResults[recursive],
        followLinks: argResults[followLinks])) {
      if (entity is File) {
        searchFile(entity, searchTerms);
      }
    }
  } else {
    searchFile(File(searchPath), searchTerms);
  }
}