C# TaskCompletionSource.TrySetResultAsync方法代码示例

        /// <summary>
        /// Starts a task that waits for the next rendering from Chrome.
        /// Chrome also renders the page loading, so if you want to see a complete rendering,
        /// only start this task once your page is loaded (which you can detect via FrameLoadEnd
        /// or your own heuristics based on evaluating JavaScript).
        /// It is your responsibility to dispose the returned Bitmap.
        /// The bitmap size is determined by the Size property set earlier.
        /// </summary>
        /// <param name="ignoreExistingScreenshot">Ignore existing bitmap (if any) and return the next avaliable bitmap</param>
        /// /// <param name="blend">Choose which bitmap to retrieve, choose <see cref="PopupBlending.Blend"/> for a merged bitmap.</param>
        /// <returns>Task&lt;Bitmap&gt;.</returns>
        public Task<Bitmap> ScreenshotAsync(bool ignoreExistingScreenshot = false, PopupBlending blend = PopupBlending.Main)
        {
            // Try our luck and see if there is already a screenshot, to save us creating a new thread for nothing.
            var screenshot = ScreenshotOrNull(blend);

            var completionSource = new TaskCompletionSource<Bitmap>();

            if (screenshot == null || ignoreExistingScreenshot)
            {
                EventHandler newScreenshot = null; // otherwise we cannot reference ourselves in the anonymous method below

                newScreenshot = (sender, e) =>
                {
                    // Chromium has rendered.  Tell the task about it.
                    NewScreenshot -= newScreenshot;

                    completionSource.TrySetResultAsync(ScreenshotOrNull());
                };

                NewScreenshot += newScreenshot;
            }
            else
            {
                completionSource.TrySetResultAsync(screenshot);
            }

            return completionSource.Task;
        }

        public static Task LoadPageAsync(IWebBrowser browser, string address = null)
        {
            var tcs = new TaskCompletionSource<bool>();

            EventHandler<LoadingStateChangedEventArgs> handler = null;
            handler = (sender, args) =>
            {
                //Wait for while page to finish loading not just the first frame
                if (!args.IsLoading)
                {
                    browser.LoadingStateChanged -= handler;
                    tcs.TrySetResultAsync(true);
                }
            };

            browser.LoadingStateChanged += handler;

            if (!string.IsNullOrEmpty(address))
            {
                browser.Load(address);
            }
            return tcs.Task;
        }