Call successively an async method and sync method

Question

I have an async method that query data from a MySql server and write them in a txt file. (I didn't find a way to return a string from an async method).

And then, I have to call a simple sync method that read the txt file.

My code looks like :

var sql = new ProjetTN.Class.SQLite();
sql.GetSens("101"); //<--- This is an async method

var SensItems = sql.ListeSens(); //<--- This method return a List<string>

But if I run the code like that, the async method will be skip and will not write the txt file. After that the sync method will be try to read the txt file but he doesn't exists, so the program will crash.

In my research, I found that I need to wait for the async method be complete so I tried :

public void CallGetSens()
{
    var task = GetSens("101");
    task.Wait();
}

When I call the methods :

var sql = new ProjetTN.Class.SQLite();
sql.CallGetSens(); //<--- This is an async method

var SensItems = sql.ListeSens(); //<--- This method return a List<string>

But this just freeze the program...

So how can I call successively an async method an then a sync method ? Otherwise, how can I return a string from an async method ?

For starters: [Asynchronous Programming with async and await](https://msdn.microsoft.com/en-us/library/mt674882.aspx). Also [Control Flow in Async Programs](https://msdn.microsoft.com/en-us/library/mt674892.aspx) — Igor, Aug 04 '16 at 15:46

score 2 · Accepted Answer · answered Aug 04 '16 at 15:43

The best way is usually to make the method that's doing the calling be async so that you can await the async call:

async Task MyMethod()
{
    var sql = new ProjetTN.Class.SQLite();
    await sql.CallGetSens(); 

    var SensItems = sql.ListeSens();
    ...
}

If that won't work for some reason, you can use .ContinueWith() to make the loading of data from the text file happen after the file has been saved:

var sql = new ProjetTN.Class.SQLite();
sql.CallGetSens().ContinueWith(t => {
    var SensItems = sql.ListeSens();
    ...
});

score 0 · Answer 2 · edited May 23 '17 at 12:14

0

You can make your async operation sync by applying async await method

This link have detailed discussion about it

also see this two stackoverflow question

Question One and Question Two

edited May 23 '17 at 12:14

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answered Aug 04 '16 at 15:44

Mostafiz

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Call successively an async method and sync method

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