在Dart中执行下一个代码之前，如何等待代码执行？

我正在

flatter

和

Dart

中开发墙纸应用程序。目前我正在使用“设置墙纸”按钮，我需要检查墙纸文件是否存在，如果需要下载，然后更改墙纸

这就是我现在所拥有的，我认为我做得很好，请注意，我是Android Java开发人员，只有大约6个月的经验，因此我在

Dart

方面的基础知识也不多，但不是很好

下载壁纸功能

static Future<int> downloadWallpaperFile(int wallpaperID,
  {String path}) async {
///Prepare a url for downloading the wallpaper using the getWallpaperURL method and passing in fullSizedWallpaper string constant
String url = getWallpaperURL(WallpaperSize.fullWallpaper, wallpaperID);

///Log output
print('CallingDownloadWallpaper : ' + url);

///Visual Feedback
wallpaperDetailsPageScaffoldGlobalKey.currentState.showSnackBar(
    new SnackBar(content: new Text('Starting Wallpaper Download...')));

///Start downloading the wallpaper file from the url
var data = http.readBytes(url);

///After download is completed
data.then((buffer) async {
  ///If filePath is not passed in as parameter
  if (path == null) {
    ///Use getPathForWallpaperFile to get a path for a wallpaper file
    path = await getPathForWallpaperFile(url);
  }

  ///Create a new file at the path, the path also includes the name of the file which is the id of the wallpaper
  File newFile = new File(path);

  ///Get write access to the newly created wallpaper file
  RandomAccessFile rf = newFile.openSync(mode: FileMode.write);

  ///Write the downloaded data to the file synchronously
  rf.writeFromSync(buffer);

  ///Save the file to the disk synchronously
  rf.flushSync();

  ///Close access to file synchronously
  rf.closeSync();

  ///Log output
  print('DownloadWallpaperResult : Complete');

  ///Visual Feedback
  wallpaperDetailsPageScaffoldGlobalKey.currentState.showSnackBar(
      new SnackBar(content: new Text('Wallpaper Download Complete')));
});
return 0;
}

static setWallpaper(int wallpaperID) async {
///Prepare variables for setting wallpaper and download the wallpaper as well (if needed)
String url = getWallpaperURL(WallpaperSize.fullWallpaper, wallpaperID);
String path = await getPathForWallpaperFile(url);
bool fileExists = checkIfFileExists(path);

///If wallpaper file does not exist then download it
if (fileExists == false) {
  ///Download wallpaper then change wallpaper
  await downloadWallpaperFile(wallpaperID, path: path).then((result) {
    ///Check if download was successful
    if (result == 0) {
      ///Change wallpaper
      AndroidInterface.setWallpaper(path);
    }
  });
} else {
  ///Wallpaper already downloaded
  ///Change wallpaper
  AndroidInterface.setWallpaper(path);
}
}

---

问题是您使用的是

then

，这是非阻塞的（基本上是使用

Future

s而不使用

wait

）的旧方法）

相反，请使用

wait

：

static Future<int> downloadWallpaperFile(int wallpaperID, {String path}) async {
  // ...

  //Start downloading the wallpaper file from the url
  final buffer = await http.readBytes(url);

  //After download is completed

  //If filePath is not passed in as parameter
  if (path == null) {
    //Use getPathForWallpaperFile to get a path for a wallpaper file
    path = await getPathForWallpaperFile(url);
  }

  // ...

  return 0;
}

静态未来下载壁纸文件（int-wallperId，{String-path}）异步{
// ...
//开始从url下载墙纸文件
最终缓冲区=等待http.readBytes（url）；
//下载完成后
//如果文件路径未作为参数传入
if（路径==null）{
//使用getPathForWallpaperFile获取墙纸文件的路径
路径=等待GetPathForWallperFile（url）；
}
// ...
返回0；
}

---

顺便说一句，

//

保留用于类和字段的文档，使用

//

进行方法内注释

---

我也不确定使用同步io操作是否是个好主意。这可能会阻塞应用程序的UI，最好使用异步io api（再次使用

wait

）。

什么不起作用？