异步替代

Question

I am trying to implement this code in my app to backup data to skydrive http://netitude.bc3tech.net/2012/07/11/skydrive-backup-of-your-mobile-applets-get-some-common-ground/

but how I can not install Async CTP (I tested during 2 - 3 days but async ctp is not installed fine...already I have tried solutions but the problems persist). Would be possible to do the same but not using async? how to wait to complete the task to continue?

using these tools "Windows Phone SDK 7.1 and 7.1.1 Update": https://dev.windowsphone.com/en-us/downloadsdk

(...)

var rootFolders = JObject.Parse((await client.GetAsyncTask("/me/skydrive/files?filter=folders,albums")).RawResult);
var progDataFolder = rootFolders["data"].FirstOrDefault(f => f.Value<string>("name").Equals("programdata", StringComparison.OrdinalIgnoreCase));
string progDataFolderId;
if (progDataFolder == null)
{
    var result = await client.PostAsyncTask("me/skydrive/",
        new Dictionary<string, object>() { { "name", "ProgramData" } });**

    progDataFolderId = JObject.Parse(result.RawResult).Value<string>("folder_id");
}
else
{
    progDataFolderId = progDataFolder.Value<string>("id");
}

var windowsPhoneFolder = JObject.Parse((await client.GetAsyncTask(string.Concat("/", progDataFolderId, "/files?filter=folders,albums"))).RawResult)["data"]
    .FirstOrDefault(f => f.Value<string>("name").Equals("windows phone", StringComparison.OrdinalIgnoreCase));
string windowsPhoneFolderId;
if (windowsPhoneFolder == null)
{
    var result = await client.PostAsyncTask(string.Concat("/", progDataFolderId),
        new Dictionary<string, object>() { { "name", "Windows Phone" } });**

    windowsPhoneFolderId = JObject.Parse(result.RawResult).Value<string>("id");
}
else
{
    windowsPhoneFolderId = windowsPhoneFolder.Value<string>("id");
}

(...)

Alternative to do this. example:

var result = await client.PostAsyncTask("me/skydrive/",
            new Dictionary<string, object>() { { "name", "ProgramData" } });

Answer 1

If you have Task s, you can use what's called "continuation passing style". Essentially, everywhere you would use await , you instead call Task.ContinueWith and pass in the rest of your method. Loops are more complex, but can also be handled with continuations.

Note that GetAsyncTask may not work correctly if you don't have the Async CTP installed correctly. So in your case, I recommend you use the Event-based Asynchronous Pattern (EAP) already supported by the LiveConnectClient class: eg, subscribe to the GetCompleted event and then call GetAsync . See this post for an example.

Answer 2

Assuming that the same code doesn't use any methods that are only available in a new version of the framework, you can simply use TPL methods to reproduce what await does. await runs continuations with the synchronization context of the code that executed the await. So, to duplicate that you need to use an overload of ContinueWith that accepts a TaskScheduler and pass in the TaskScheduler from the current context. For example:

TaskScheduler taskScheduler = TaskScheduler.FromCurrentSynchronizationContext();
client.PostAsyncTask("me/skydrive/", new Dictionary<string, object>() {{"name", "ProgramData"}})
    .ContinueWith(t =>
                    {
                    progDataFolderId= JObject.Parse(result.RawResult).Value<string>("folder_id");
                    });

Now, that's the simple part of getting one await translated to a TPL method with a task scheduler. What the compiler is actually doing is creating a state machine in your async method (the method with all the await code). That state machine has broken up your original code into chunks and keeping track of various things like progDataFolder == null because, in your case, the code after the first else can be invoked in two different ways. One is asynchronous--if progDataFolder is null then the code after the else is invoked asynchronously, if progDataFolder is not null the the progDataFolderId is set from the progDataFolder instance and the code after the else is involved synchronously . So, you'll have to mode that properly with TPL methods. ie you won't run the code after the else in a continuation when progDataFolder is not null .