chromium源码中下面的函数具体功能，详细解释一下：
base::WeakPtr<content::NavigationHandle> Navigate
(NavigateParams* params
) {
TRACE_EVENT1
("navigation", "chrome::Navigate", "disposition",
params
->disposition
);
Browser* source_browser = params
->browser;
if
(source_browser
) {
params
->initiating_profile = source_browser
->profile
();
}
DCHECK
(params
->initiating_profile
);
// If the
created window is a partitioned popin, a valid source exists, and
// the disposition is NEW_POPUP then the resulting popup should
be tab
-modal
.
// See: https://explainers
-by
-googlers
.github
.io/partitioned
-popins/
params
->is_tab_modal_popup
|=
params
->window_features
.is_partitioned_popin && params
->source_contents &&
params
->disposition == WindowOpenDisposition::NEW_POPUP;
#if BUILDFLAG
(IS_CHROMEOS
)
if
(params
->initiating_profile
->IsOffTheRecord
() &&
params
->initiating_profile
->GetOTRProfileID
().IsCaptivePortal
() &&
params
->disposition != WindowOpenDisposition::NEW_POPUP &&
params
->disposition != WindowOpenDisposition::CURRENT_TAB &&
!IncognitoMode
Forced
(params
->initiating_profile
)) {
// Navigation outside of the current tab or the initial popup window from a
// captive portal signin window should
be prevented
.
params
->disposition = WindowOpenDisposition::CURRENT_TAB;
}
#endif
if
(params
->initiating_profile
->ShutdownStarted
()) {
// Don't navigate when the profile is shutting down
.
return nullptr;
}
// Block navigation requests when in locked fullscreen mode
. We allow
// navigation requests in the webapp when locked
for OnTask
(only relevant
for
//
non
-web browser scenarios
).
// TODO
(b/365146870
): Remove once we consolidate locked fullscreen with
// OnTask
.
if
(source_browser
) {
bool should_block_navigation =
plat
form_util::IsBrowserLockedFullscreen
(source_browser
);
#if BUILDFLAG
(IS_CHROMEOS
)
if
(source_browser
->IsLocked
ForOnTask
()) {
should_block_navigation = false;
}
#endif // BUILDFLAG
(IS_CHROMEOS
)
if
(should_block_navigation
) {
return nullptr;
}
}
// Open System Apps in their standalone window if necessary
.
// TODO
(crbug
.com/40136163
): Remove this code after we integrate with intent
// handling
.
#if BUILDFLAG
(IS_CHROMEOS
)
const std::optional<ash::SystemWebAppType> capturing_system_app_type =
ash::GetCapturingSystemApp
ForURL
(params
->initiating_profile, params
->url
);
if
(capturing_system_app_type &&
(!params
->browser
||
!ash::IsBrowser
ForSystemWebApp
(params
->browser,
capturing_system_app_type
.value
()))) {
ash::SystemAppLaunchParams swa_params;
swa_params
.url = params
->url;
ash::LaunchSystemWebAppAsync
(params
->initiating_profile,
capturing_system_app_type
.value
(), swa_params
);
// It's okay to early return here,
because LaunchSystemWebAppAsync uses a
// different logic to choose
(and create if necessary
) a browser window
for
// system apps
.
//
// It's okay to skip the checks and cleanups
below
. The link captured system
// app will either open in its own browser window, or navigate an existing
// browser window exclusively used by this app
. For the initiating browser,
// the navigation should appear to
be cancelled
.
return nullptr;
}
#endif // BUILDFLAG
(IS_CHROMEOS
)
#if !BUILDFLAG
(IS_ANDROID
)
//
Force isolated PWAs to open in an app window
.
params
->
force_open_pwa_window =
content::SiteIsolationPolicy::ShouldUrlUseApplicationIsolationLevel
(
params
->initiating_profile, params
->url
);
params
->open_pwa_window_if_possible
|= params
->
force_open_pwa_window;
#endif
if
(!AdjustNavigateParams
ForURL
(params
)) {
return nullptr;
}
// Picture
-in
-picture browser windows must have a source contents in order
for
// the window to function correctly
. If we have
no source contents to work
// with
(e
.g
. if an extension popup attempts to open a PiP window
), we should
// cancel the navigation
. The source URL must also
be of a type that's
// allowed to open document PiP
. See `PictureInPictureWindowManager`
for
// details on what's allowed
.
if
(params
->disposition == WindowOpenDisposition::NEW_PICTURE_IN_PICTURE
) {
const GURL& url = params
->source_contents
? params
->source_contents
->GetLastCommittedURL
()
: GURL
();
if
(!PictureInPictureWindowManager::IsSupported
ForDocumentPictureInPicture
(
url
)) {
return nullptr;
}
}
// If
no source WebContents was specified, we use the selected one from the
// target browser
. This must happen
before GetBrowserAndTab
ForDisposition
()
// has a chance to replace
|params
->browser
| with a
nother one, but after the
// above check that relies on the original source_contents value
.
if
(!params
->source_contents && params
->browser
) {
params
->source_contents =
params
->browser
->tab_strip_model
()->GetActiveWebContents
();
}
WebContents* contents_to_navigate_or_insert =
params
->contents_to_insert
.get
();
if
(params
->switch_to_singleton_tab
) {
DCHECK_EQ
(params
->disposition, WindowOpenDisposition::SINGLETON_TAB
);
contents_to_navigate_or_insert = params
->switch_to_singleton_tab;
}
#if !BUILDFLAG
(IS_ANDROID
)
// If this is a Picture in Picture window, then
notify the pip manager about
// it
. This enables the opener and pip window to stay connected, so that
(for
// example
), the pip window does
not outlive the opener
.
//
// We do this
before creating the browser window, so that the browser can talk
// to the PictureInPictureWindowManager
. Otherwise, the manager has
no idea
// that there's a pip window
.
if
(params
->disposition == WindowOpenDisposition::NEW_PICTURE_IN_PICTURE
) {
// Picture in picture windows may
not
be opened by other picture in
// picture windows, or without an opener
.
if
(!params
->browser
|| params
->browser
->is_type_picture_in_picture
()) {
params
->browser = nullptr;
return nullptr;
}
PictureInPictureWindowManager::Get
Instance()->EnterDocumentPictureInPicture
(
params
->source_contents, contents_to_navigate_or_insert
);
}
#endif // !BUILDFLAG
(IS_ANDROID
)
// TODO
(crbug
.com/364657540
): Revisit integration with web_application system
// later if needed
.
int singleton_index;
#if !BUILDFLAG
(IS_ANDROID
)
std::unique_ptr<web_app::NavigationCapturingProcess> app_navigation =
web_app::NavigationCapturingProcess::May
beHandleAppNavigation
(*params
);
std::optional<std::tuple<Browser*, int>> app_browser_tab_override;
if
(app_navigation
) {
app_browser_tab_override =
app_navigation
->GetInitialBrowserAndTabOverride
ForNavigation
(*params
);
}
std::tie
(params
->browser, singleton_index
) =
app_browser_tab_override
.has_value
()
? *app_browser_tab_override
: GetBrowserAndTab
ForDisposition
(*params
);
#else // !BUILDFLAG
(IS_ANDROID
)
std::tie
(params
->browser, singleton_index
) =
GetBrowserAndTab
ForDisposition
(*params
);
#endif
if
(!params
->browser
) {
return nullptr;
}
// Trying to open a background tab when in a
non
-tab
bed app browser results in
// focusing a regular browser window and opening a tab in the background
// of that window
. Change the disposition to NEW_
FOREGROUND_TAB so that
// the new tab is focused
.
if
(source_browser && source_browser
->is_type_app
() &&
params
->disposition == WindowOpenDisposition::NEW_BACKGROUND_TAB &&
!
(source_browser
->app_controller
() &&
source_browser
->app_controller
()->has_tab_strip
())) {
params
->disposition = WindowOpenDisposition::NEW_
FOREGROUND_TAB;
}
if
(singleton_index !=
-1
) {
contents_to_navigate_or_insert =
params
->browser
->tab_strip_model
()->GetWebContentsAt
(singleton_index
);
} else if
(params
->disposition == WindowOpenDisposition::SWITCH_TO_TAB
) {
// The user is trying to open a tab that
no longer exists
. If we open a new
// tab, it
could leave orphaned NTPs around, but always overwriting the
// current tab
could could clob
ber state that the user was trying to
// preserve
. Fallback to the
behavior used
for singletons: overwrite the
// current tab if it's the NTP, otherwise open a new tab
.
params
->disposition = WindowOpenDisposition::SINGLETON_TAB;
ShowSingletonTabOverwritingNTP
(params
);
return nullptr;
}
if
(params
->
force_open_pwa_window
) {
CHECK
(web_app::AppBrowserController::IsWebApp
(params
->browser
));
}
#if BUILDFLAG
(IS_CHROMEOS
)
if
(source_browser && source_browser != params
->browser
) {
// When the newly
created browser was spawned by a browser which visits
// a
nother user's desktop, it should
be shown on the same desktop as the
// originating one
. (This is part of the desktop separation per profile
).
auto* window_manager = MultiUserWindowManagerHelper::GetWindowManager
();
// Some unit tests have
no client instantiated
.
if
(window_manager
) {
aura::Window* src_window = source_browser
->window
()->GetNativeWindow
();
aura::Window* new_window = params
->browser
->window
()->GetNativeWindow
();
const AccountId& src_account_id =
window_manager
->GetUserPresentingWindow
(src_window
);
if
(src_account_id !=
window_manager
->GetUserPresentingWindow
(new_window
)) {
// Once the window gets presented, it should
be shown on the same
// desktop as the desktop of the creating browser
. Note that this
// command will
not show the window if it wasn't shown yet by the
// browser creation
.
window_manager
->ShowWindow
ForUser
(new_window, src_account_id
);
}
}
}
#endif
// Navigate
() must
not return early after this point
.
if
(GetSourceProfile
(params
) != params
->browser
->profile
()) {
// A tab is
being opened from a link from a different profile, we must reset
// source in
formation that may cause state to
be shared
.
params
->opener = nullptr;
params
->source_contents = nullptr;
params
->source_site_
instance = nullptr;
params
->referrer = content::Referrer
();
}
// Make sure the Browser is shown if params call
for it
.
ScopedBrowserShower shower
(params, &contents_to_navigate_or_insert
);
if
(params
->is_tab_modal_popup
) {
shower
.set_source_contents
(params
->source_contents
);
}
// Some dispositions need coercion to base types
.
NormalizeDisposition
(params
);
// If a new window has
been
created, it needs to
be shown
.
if
(params
->window_
action == NavigateParams::
NO_
ACTION &&
source_browser != params
->browser &&
params
->browser
->tab_strip_model
()->empty
()) {
params
->window_
action = NavigateParams::SHOW_WINDOW;
}
// If we create a popup window from a
non user
-gesture, don't activate it
.
if
(params
->window_
action == NavigateParams::SHOW_WINDOW &&
params
->disposition == WindowOpenDisposition::NEW_POPUP &&
params
->user_gesture == false
) {
params
->window_
action = NavigateParams::SHOW_WINDOW_INACTIVE;
}
// Determine if the navigation was user initiated
. If it was, we need to
// in
form the target WebContents, and we may need to update the UI
.
bool user_initiated =
params
->transition & ui::PAGE_TRANSITION_FROM_ADDRESS_BAR
||
!ui::PageTransitionIsWebTriggerable
(params
->transition
);
base::WeakPtr<content::NavigationHandle> navigation_handle;
std::unique_ptr<tabs::TabModel> tab_to_insert;
if
(params
->contents_to_insert
) {
tab_to_insert =
std::make_unique<tabs::TabModel>
(std::move
(params
->contents_to_insert
),
params
->browser
->tab_strip_model
());
}
// If
no target WebContents was specified
(and we didn't seek and find a
// singleton
), we need to construct one if we are supposed to target a new
// tab
.
if
(!contents_to_navigate_or_insert
) {
DCHECK
(!params
->url
.is_empty
());
if
(params
->disposition != WindowOpenDisposition::CURRENT_TAB
) {
tab_to_insert = std::make_unique<tabs::TabModel>
(
CreateTargetContents
(*params, params
->url
),
params
->browser
->tab_strip_model
());
contents_to_navigate_or_insert = tab_to_insert
->GetContents
();
apps::SetAppId
ForWebContents
(params
->browser
->profile
(),
contents_to_navigate_or_insert,
params
->app_id
);
#if BUILDFLAG
(ENABLE_CAPTIVE_PORTAL_DETECTION
)
captive_portal::CaptivePortalTabHelper::FromWebContents
(
contents_to_navigate_or_insert
)
->set_window_type
(params
->captive_portal_window_type
);
#endif
} else {
//
... otherwise if we're loading in the current tab, the target is the
// same as the source
.
DCHECK
(params
->source_contents
);
contents_to_navigate_or_insert = params
->source_contents;
}
// Try to handle
non
-navigational URLs that popup dialogs and such, these
// should
not actually navigate
.
if
(!Handle
NonNavigationAboutURL
(params
->url
)) {
// Per
form the actual navigation, tracking whether it came from the
// renderer
.
navigation_handle = LoadURLInContents
(contents_to_navigate_or_insert,
params
->url, params
);
}
} else {
//
|contents_to_navigate_or_insert
| was specified
non
-NULL, and so we assume
// it has already
been navigated appropriately
. We need to do
nothing more
// other than add it to the appropriate tabstrip
.
}
// If the user navigated from the omnibox, and the selected tab is going to
// lose focus, then make sure the focus
for the source tab goes away from the
// omnibox
.
if
(params
->source_contents &&
(params
->disposition == WindowOpenDisposition::NEW_
FOREGROUND_TAB
||
params
->disposition == WindowOpenDisposition::NEW_WINDOW
) &&
(params
->tabstrip_add_types & AddTabTypes::ADD_INHERIT_OPENER
)) {
params
->source_contents
->Focus
();
}
if
(tab_to_insert
) {
// Save data needed
for link capturing into apps that can
not otherwise
be
// inferred later in the navigation
. These are only needed when the
// navigation happens in a different tab to the link click
.
apps::SetLinkCapturingSourceDisposition
(tab_to_insert
->GetContents
(),
params
->disposition
);
}
if
(params
->source_contents == contents_to_navigate_or_insert
) {
// The navigation occurred in the source tab
.
params
->browser
->UpdateUI
ForNavigationInTab
(
contents_to_navigate_or_insert, params
->transition,
params
->window_
action, user_initiated
);
} else if
(singleton_index ==
-1
) {
if
(source_browser != params
->browser
) {
params
->tabstrip_index = params
->browser
->tab_strip_model
()->count
();
}
// If some
non
-default value is set
for the index, we should tell the
// TabStripModel to respect it
.
if
(params
->tabstrip_index !=
-1
) {
params
->tabstrip_add_types
|= AddTabTypes::ADD_
FORCE_INDEX;
}
// May
be notify that an open operation has
been done from a gesture
.
// TODO
(crbug
.com/40719979
): preferably pipe this in
formation through the
// TabStripModel instead
. See bug
for deeper discussion
.
if
(params
->user_gesture && source_browser == params
->browser
) {
params
->browser
->window
()->LinkOpeningFromGesture
(params
->disposition
);
}
DCHECK
(tab_to_insert
);
// The navigation should insert a new tab into the target Browser
.
params
->browser
->tab_strip_model
()->AddTab
(
std::move
(tab_to_insert
), params
->tabstrip_index, params
->transition,
params
->tabstrip_add_types, params
->group
);
}
if
(singleton_index >= 0
) {
// If switching browsers, make sure it is shown
.
if
(params
->disposition == WindowOpenDisposition::SWITCH_TO_TAB &&
params
->browser != source_browser
) {
params
->window_
action = NavigateParams::SHOW_WINDOW;
}
if
(contents_to_navigate_or_insert
->IsCrashed
()) {
contents_to_navigate_or_insert
->GetController
().Reload
(
content::ReloadType::
NORMAL, true
);
} else if
(params
->
path_
behavior == NavigateParams::IG
NORE_AND_NAVIGATE &&
contents_to_navigate_or_insert
->GetURL
() != params
->url
) {
navigation_handle = LoadURLInContents
(contents_to_navigate_or_insert,
params
->url, params
);
}
// If the singleton tab isn't already selected, select it
.
if
(params
->source_contents != contents_to_navigate_or_insert
) {
// Use the index
before the potential close
below,
because it
could
// make the index refer to a different tab
.
auto gesture_type = user_initiated
? TabStripUserGestureDetails::GestureType::kOther
: TabStripUserGestureDetails::GestureType::k
None;
bool should_close_this_tab = false;
if
(params
->disposition == WindowOpenDisposition::SWITCH_TO_TAB
) {
// Close orphaned NTP
(and the like
) with
no history when the user
// switches away from them
.
if
(params
->source_contents
) {
if
(params
->source_contents
->GetController
().CanGoBack
() ||
(params
->source_contents
->GetLastCommittedURL
().spec
() !=
chrome::kChromeUINewTabURL &&
params
->source_contents
->GetLastCommittedURL
().spec
() !=
url::kAboutBlankURL
)) {
// Blur location bar
before state save in ActivateTabAt
() below
.
params
->source_contents
->Focus
();
} else {
should_close_this_tab = true;
}
}
}
params
->browser
->tab_strip_model
()->ActivateTabAt
(
singleton_index, TabStripUserGestureDetails
(gesture_type
));
// Close tab after switch so index remains correct
.
if
(should_close_this_tab
) {
params
->source_contents
->Close
();
}
}
}
params
->navigated_or_inserted_contents = contents_to_navigate_or_insert;
// At this point, the `params
->navigated_or_inserted_contents` is guaranteed to
//
be non null, so per
form tasks if the navigation has
been captured by a web
// app, like enqueueing launch params
.
#if !BUILDFLAG
(IS_ANDROID
)
if
(app_navigation
) {
web_app::NavigationCapturingProcess::AfterWebContentsCreation
(
std::move
(app_navigation
), *params
->navigated_or_inserted_contents,
navigation_handle
.get
());
}
#endif // !BUILDFLAG
(IS_ANDROID
)
return navigation_handle;
}
本文针对Struts框架中出现的NullPointerException错误进行了详细分析，并提供了解决方案。通过在struct-config.xml文件中添加特定配置，成功解决了No action instance for path/leftTreeMenu could be created的问题。
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