Question

In my Windows Phone Applicarion I need to implement logic to start some Method every 20 days, how can I implement this?

public void Method()
{
//some logic

}

Update
For example I can fix the first start of some method, then every start of application I will fix the current date time and them calculate the differens, and if the difference between the last and first sstart of some method will be more than 30 days I will start Method(). So how can I calculate the difference (days)?

Answer 1

So you want to know if it’s 20 (or more?) days since you last performed an action in your app.

Let’s assume that you save the date to calculate from as a DateTime called savedDate. (I’m assuming you can put this in and retrieve from IsolatedStorage without issue.)
Then you can just do a simple test against the current date:

if (saveddate.Date.AddDays(20) <= DateTime.UtcNow.Date)
{
    // Do your every 20 days action here 
    // and then probably reset savedDate to the current date?
}