为什么MS强迫我进入异步操作？

Question

我需要从资源中的文本文件中读取数值(版本号).我将此版本号与已安装组件的版本号进行比较.如果资源中的版本号高于安装的版本,我将新组件(数据库)从我的资源复制到用户可以使用它的本地目录.

我需要同步执行此操作,因为没有数据库我的应用程序无法工作.

但是,我没有看到任何同步的方法.MS强迫我用这样的异步任务来做:

private async Task<string> ResourcesReadTextFile(string uFileName)
{
    string sRet = "";

    try
    {
        StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(new Uri(cstAssets + uFileName));
        using (var inputStream = await file.OpenReadAsync())
        using (var classicStream = inputStream.AsStreamForRead())
        using (var streamReader = new StreamReader(classicStream))
        {
            while (streamReader.Peek() >= 0)
            {
                sRet = streamReader.ReadLine();
            }
        }
    }
    catch (Exception ex)
    {
        Debug.Assert(false);//check here
    }
    return sRet;
}

现在我遇到了应用程序在数据库被复制到本地目录之前启动的情况,因为复制也需要异步完成,根本没有任何方法可以同步.没有StorageFile.Copy()这样的功能.

我之所以使用的是:

private async void pCopyFromResourcesToLocal(string uFileName)
{
    // Cant await inside catch, but this works anyway
    try
    {
        StorageFile storfile = await StorageFile.GetFileFromApplicationUriAsync(new Uri(cstAssets + uFileName));
        await storfile.CopyAsync(ApplicationData.Current.LocalFolder);
    }
    catch (Exception ex)
    {
        Debug.WriteLine("");
    }
}

这让我发疯了.

人们写道Async应该被拥抱和拥抱并欣赏,但在我的情况下它只会导致麻烦.

我没有看到任何让这个东西同步的方法,我想知道为什么MS强迫我这样做.

任何帮助非常感谢.

谢谢.

代码截图:

编辑:我在这里添加了顶级方法:

    public static async Task<DB> InitAppDb()
    {
        IFileHelper helper = DependencyService.Get<IFileHelper>();
        string path = await helper.GetFilePathAndCopyFromResourcesIfNotPresent("tablet.db");

        return (_dbApp = new DB(path));
    }

    public async Task CopyDatabaseIfNotExists(string uFileName)
    {
        IsolatedStorageFile nExpectedFolder = IsolatedStorageFile.GetUserStoreForApplication();
        bool bCopyNewDB = false;

        Task<bool> datatask = pResourceIsNewer(uFileName);
        bCopyNewDB = await datatask;

        if (! bCopyNewDB)
        {
            try
            {
                await ApplicationData.Current.LocalFolder.GetFileAsync(uFileName); //nExpectedFolder.GetFileAsync(dbPath);/// ApplicationData.Current.LocalFolder.GetFileAsync("preinstalledDB.db");
                // No exception means it exists
                return;
            }
            catch (System.IO.FileNotFoundException)
            {
                // The file obviously doesn't exist
            }
        }

        pCopyFromResourcesToLocal(uFileName);

    }

    private async Task<bool>pResourceIsNewer(string uPath)
    {
        string sFileNameAppDBVersion =uPath + ".txt";

        if (IsolatedStorageFileExist(sFileNameAppDBVersion))
        {
            int iAppDBVersionInstalled = Convert.ToInt32(IsolatedStorageReadTextFile(sFileNameAppDBVersion));

            Task<string> datatask = ResourcesReadTextFile(sFileNameAppDBVersion);
            string s = await datatask;

            int iAppDBResources = Convert.ToInt32(s);

            bool b = (iAppDBResources > iAppDBVersionInstalled);
            return b;
        }
        else
        {
            return true;
        }
    }

Answer 1

你所要做的就是:

//private async void pCopyFromResourcesToLocal(string uFileName) { ... }
  private async Task pCopyFromResourcesToLocal(string uFileName) { ... }

然后你可以等待它:

//pCopyFromResourcesToLocal(uFileName);
  await pCopyFromResourcesToLocal(uFileName);

它会在你打电话之前完成 return (_dbApp = new DB(path));

此async/ await链中的任何内容都不会发生故障.