Using the TelemetryClient in Applicationinsightss works only when the client is instantiated in a TelemetryConfiguration`s using statement

I am working with ApplicationInsights, defining and sending my own custom events.

I use the telemetryclient for that. It works only if I instantiate and use my telemetryclient object as following:

TelemetryClient telemetryClient;
using (var telemetryConfiguration = new TelemetryConfiguration("instrumentationKey"))
{
    telemetryClient = new TelemetryClient(telemetryConfiguration);

    telemetryClient.TrackEvent("CustomEvent1");

    telemetryClient.Flush();
    Thread.Sleep(5000);
}

The problem is, that I want to inject the telemtryClient in different services. Yet calling this call at the same Position generates no Events in the portal:

TelemetryClient telemetryClient;
using (var telemetryConfiguration = new TelemetryConfiguration("instrumentationKey"))
{
    telemetryClient = new TelemetryClient(telemetryConfiguration);

}


telemetryClient.TrackEvent("CustomEvent1");

telemetryClient.Flush();
Thread.Sleep(5000);

Is that the wrong way to use the telemtryClient?

If you are writing a .Net Core Application you can configure dependency Injection of the TelemetryClient in the ConfigureServices method of your Startup.cs. See here for a complete example.

public void ConfigureServices(IServiceCollection services)
{
        ...
        services.AddApplicationInsightsTelemetry();
        ...
}

Then, if you are writing a Mvc app, for example, you can inject the TelemetryClient in your controllers like this:

private readonly TelemetryClient tc;

public MyController(TelemetryClient _tc)
{
    tc = _tc;
} 

public HttpResponseMessage Get(int id)
{
    tc.TrackEvent("CustomEvent1");
    ...
}

Make sure to also configure your appsettings.json correctly:

"ApplicationInsights": {
"InstrumentationKey": "..." }

Hope this helps, Andreas