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await WaitForThatEvent()<br />
DoSomethingAfterward()

method()
{
    // some code
    WhatEver.MyEvent += (myArgs) => {
       // Do your stuffs here.
       // You might create a named delegate if you want this event to handled only one time.
    }
}

EventHandler ev = null;
ev = (o, e) => {
  source.Event -= eh;
  DoSomething();
};
source.Event += eh;

await source.Event.WaitForEvent()
DoSomething();

source.Event += (o, e) => {
  source.Event -= eh;
  DoSomething();
};

oArgType o; 
hArgType h;
await source.Event.WaitForEvent(out o, out h);
DoSomething(o, h);

public static Task<GpsLocationArgs> WaitForLocationChangedAsync(this IGps gps)
{
    var res = new TaskCompletionSource<GpsLocationArgs>();
    EventHandler<GpsLocation> eh = null;
    eh = (o, e) =>
    {
        gps.LocationChanged -= eh;
        res.TrySetResult(e);
    };
    gps.LocationChanged += eh;
    return res.Task;
}
// ....
var loc = await myGps.WaitForLocationChangedAsync();
Console.WriteLine($"({loc.Latitude}, {loc.Longitude})");