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