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Author: mohamedosama914

Public/DefaultFocusHandler.cs

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+// Copyright © 2014 The CefSharp Authors. All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.
+
+namespace CefSharp.WinForms.Internals
+{
+    /// <summary>
+    /// Default implementation of <see cref="IFocusHandler" />
+    /// for the WinForms implementation
+    /// </summary>
+    /// <seealso cref="CefSharp.IFocusHandler" />
+    public class DefaultFocusHandler : IFocusHandler
+    {
+        private bool initialFocusOnNavigation;
+        /// <summary>
+        /// Called when the browser component has received focus.
+        /// </summary>
+        /// <param name="chromiumWebBrowser">the ChromiumWebBrowser control</param>
+        /// <param name="browser">the browser object</param>
+        /// <remarks>Try to avoid needing to override this logic in a subclass. The implementation in
+        /// DefaultFocusHandler relies on very detailed behavior of how WinForms and
+        /// Windows interact during window activation.</remarks>
+        public virtual void OnGotFocus(IWebBrowser chromiumWebBrowser, IBrowser browser)
+        {
+            //We don't deal with popups as they're rendered by default entirely by CEF
+            //For print dialogs the browser will be null, we don't want to deal with that either.
+            if (browser == null || browser.IsPopup)
+            {
+                return;
+            }
+
+            var winFormsChromiumWebBrowser = (ChromiumWebBrowser)chromiumWebBrowser;
+            // During application activation, CEF receives a WM_SETFOCUS
+            // message from Windows because it is the top window 
+            // on the CEF UI thread.
+            //
+            // If the WinForm ChromiumWebBrowser control is the 
+            // current .ActiveControl before app activation 
+            // then we MUST NOT try to reactivate the WinForm
+            // control during activation because that will 
+            // start a race condition between reactivating
+            // the CEF control AND having another control 
+            // that should be the new .ActiveControl.
+            //
+            // For example:
+            // * CEF control has focus, and thus ChromiumWebBrowser
+            //   is the current .ActiveControl
+            // * Alt-Tab to another application
+            // * Click a non CEF control in the WinForms application.
+            // * This begins the Windows activation process.
+            // * The WM_ACTIVATE process on the WinForm UI thread
+            //   will update .ActiveControl to the clicked control.
+            //   The clicked control will receive WM_SETFOCUS as well. 
+            //   (i.e. OnGotFocus)
+            //   If the ChromiumWebBrowser was the previous .ActiveControl,
+            //   then we set .Activating = true.
+            // * The WM_ACTIVATE process on the CEF thread will
+            //   send WM_SETFOCUS to CEF thus staring the race of
+            //   which will end first, the WndProc WM_ACTIVATE process
+            //   on the WinForm UI thread or the WM_ACTIVATE process
+            //   on the CEF UI thread.
+            // * CEF will then call this method on the CEF UI thread
+            //   due to WM_SETFOCUS.
+            // * This method will clear the activation state (if any)
+            //   on the ChromiumWebBrowser control, due to the race
+            //   condition the WinForm UI thread cannot.
+            if (winFormsChromiumWebBrowser.IsActivating)
+            {
+                winFormsChromiumWebBrowser.IsActivating = false;
+            }
+            else
+            {
+                // Otherwise, we're not being activated
+                // so we must activate the ChromiumWebBrowser control
+                // for WinForms focus tracking.
+                winFormsChromiumWebBrowser.InvokeOnUiThreadIfRequired(() =>
+                {
+                    winFormsChromiumWebBrowser.Activate();
+                });
+            }
+        }
+
+        /// <summary>
+        /// Called when the browser component is requesting focus.
+        /// </summary>
+        /// <param name="chromiumWebBrowser">the ChromiumWebBrowser control</param>
+        /// <param name="browser">the browser object</param>
+        /// <param name="source">Indicates where the focus request is originating from.</param>
+        /// <returns>Return false to allow the focus to be set or true to cancel setting the focus.</returns>
+        public virtual bool OnSetFocus(IWebBrowser chromiumWebBrowser, IBrowser browser, CefFocusSource source)
+        {
+            //We don't deal with popups as they're rendered by default entirely by CEF
+            if (browser.IsPopup)
+            {
+                return false;
+            }
+
+            var focusSourceNavigation = source == CefFocusSource.FocusSourceNavigation;
+
+            var winFormsBrowser = (ChromiumWebBrowser)chromiumWebBrowser;
+
+            //The default behaviour when browser is activated by default
+            //This was the default prior to version 73
+            if (winFormsBrowser.ActivateBrowserOnCreation)
+            {
+                // Do not let the browser take focus when a Load method has been called
+                return focusSourceNavigation;
+            }
+
+            //For the very first navigation we let the browser
+            //take focus so touch screens work correctly.
+            //See https://github.com/cefsharp/CefSharp/issues/2776
+            if (!initialFocusOnNavigation && focusSourceNavigation)
+            {
+                initialFocusOnNavigation = true;
+
+                return false;
+            }
+
+            // Do not let the browser take focus when a Load method has been called
+            return focusSourceNavigation;
+        }
+
+        /// <summary>
+        /// Called when the browser component is about to lose focus.
+        /// For instance, if focus was on the last HTML element and the user pressed the TAB key.
+        /// </summary>
+        /// <param name="chromiumWebBrowser">the ChromiumWebBrowser control</param>
+        /// <param name="browser">the browser object</param>
+        /// <param name="next">Will be true if the browser is giving focus to the next component
+        /// and false if the browser is giving focus to the previous component.</param>
+        public virtual void OnTakeFocus(IWebBrowser chromiumWebBrowser, IBrowser browser, bool next)
+        {
+            //We don't deal with popups as they're rendered by default entirely by CEF
+            if (browser.IsPopup)
+            {
+                return;
+            }
+
+            var winFormsChromiumWebBrowser = (ChromiumWebBrowser)chromiumWebBrowser;
+
+            // NOTE: OnTakeFocus means leaving focus / not taking focus
+            winFormsChromiumWebBrowser.InvokeOnUiThreadIfRequired(() => winFormsChromiumWebBrowser.SelectNextControl(next));
+        }
+    }
+}