如何在超时后关闭活动

我在安卓应用程序中有登录屏幕，它有45秒的超时期，它还显示弹出窗口"超时"，但在该活动没有关闭或完成后，点击弹出应用程序崩溃

public HttpClient Client
        {
            get
            {
                if (_client != null) return _client;

                var httpClient = new HttpClient(new NativeMessageHandler {UseCookies = false});
                httpClient.BaseAddress = new Uri(ApplicationSettings.BaseServiceUrl);
                httpClient.Timeout = TimeSpan.FromMilliseconds(45000);
                return _client = httpClient;
            }
        }
        public HttpClient ClientPreAuthenticated
        {
            get
            {
                if (_client != null) return _client;
                var httpClient = new HttpClient(new NativeMessageHandler { UseCookies = false, PreAuthenticate = true });
                httpClient.BaseAddress = new Uri(ApplicationSettings.BaseServiceUrl);
                httpClient.Timeout = TimeSpan.FromMilliseconds(45000);
                return _client = httpClient;
            }
        }

建议我关闭此活动的任何代码