OnBeforeNavigate Event

In This Topic

Description

Fired before a Frame loads a new URL. The event is classified as synchronous and for performance reasons is disabled by default. Read remarks section below to enable it.

Syntax

Visual Basic
Public Event OnBeforeNavigate( _ ByVal Id As Long, _ ByVal BrowserID As Long, _ ByVal FrameID As Long, _ ByVal FrameName As String, _ ByVal IsRedirect As Boolean, _ ByVal ResourceType As NAV_RESOURCE_TYPE, _ ByVal TransitionType As NAV_TRANSITION_TYPE, _ ByVal Method As String, _ ByVal ReferrerURL As String, _ ByVal CurrentURL As String, _ ByRef NewURL As String, _ ByRef Cancel As Boolean _ )

Visual Basic

Public Event OnBeforeNavigate( _
   ByVal Id As Long, _
   ByVal BrowserID As Long, _
   ByVal FrameID As Long, _
   ByVal FrameName As String, _
   ByVal IsRedirect As Boolean, _
   ByVal ResourceType As NAV_RESOURCE_TYPE, _
   ByVal TransitionType As NAV_TRANSITION_TYPE, _
   ByVal Method As String, _
   ByVal ReferrerURL As String, _
   ByVal CurrentURL As String, _
   ByRef NewURL As String, _
   ByRef Cancel As Boolean _
)

Parameters

Id

The HTTP Request identifier.

BrowserID

The Browser identifier.

FrameID

The Frame identifier.

FrameName

The Frame name (if any).

IsRedirect

Indicates if the navigation is an HTTP redirect.

ResourceType

Value	Description
RT_CSP_REPORT	A report of Content Security Policy violations.
RT_FAVICON	Favicon.
RT_FONT_RESOURCE	Font.
RT_IMAGE	Image (jpg/gif/png/etc).
RT_MAIN_FRAME	Top level page.
RT_MEDIA	Media resource.
RT_OBJECT	Object (or embed) tag for a plugin, or a resource that a plugin requested.
RT_PING	A request for a <ping>
RT_PLUGIN_RESOURCE	A resource that a plugin requested.
RT_PREFETCH	Explicitly requested prefetch.
RT_SCRIPT	External script.
RT_SERVICE_WORKER	Main resource of a service worker.
RT_SHARED_WORKER	Main resource of a shared worker.
RT_STYLESHEET	CSS stylesheet.
RT_SUB_FRAME	Frame or iframe.
RT_SUB_RESOURCE	Some other sub resource. This is the default type if the actual type is unknown.
RT_WORKER	Main resource of a dedicated worker.
RT_XHR	XMLHttpRequest.

TransitionType

Value	Description
TT_AUTO_SUBFRAME	Source is a subframe navigation. This is any content that is automatically loaded in a non-toplevel frame. For example, if a page consists of several frames containing ads, those ad URLs will have this transition type. The user may not even realize the content in these pages is a separate frame, so may not care about the URL.
TT_BLOCKED_FLAG	Attempted to visit a URL but was blocked.
TT_CHAIN_END_FLAG	The last transition in a redirect chain.
TT_CHAIN_START_FLAG	The beginning of a navigation chain.
TT_CLIENT_REDIRECT_FLAG	Redirects caused by JavaScript or a meta refresh tag on the page.
TT_DIRECT_LOAD_FLAG
TT_EXPLICIT	Source is some other "explicit" navigation action such as creating a new browser or using the LoadURL function. This is also the default value for navigations where the actual type is unknown.
TT_FORM_SUBMIT	Source is a form submission by the user. NOTE: In some situations submitting a form does not result in this transition type. This can happen if the form uses a script to submit the contents.
TT_FORWARD_BACK_FLAG	Used the Forward or Back function to navigate among browsing history.
TT_IS_REDIRECT_MASK	Used to test whether a transition involves a redirect.
TT_LINK	Source is a link click or the JavaScript window.open function. This is also the default value for requests like sub-resource loads that are not navigations.
TT_MANUAL_SUBFRAME	Source is a subframe navigation explicitly requested by the user that will generate new navigation entries in the back/forward list. These are probably more important than frames that were automatically loaded in the background because the user probably cares about the fact that this link was loaded.
TT_QUALIFIER_MASK	General mask defining the bits used for the qualifiers.
TT_RELOAD	Source is a "reload" of the page via the Reload function or by re-visiting the same URL. NOTE: This is distinct from the concept of whether particular load uses "reload semantics" (i.e. bypasses cached data).
TT_SERVER_REDIRECT_FLAG	Redirects caused by JavaScript or a meta refresh tag on the page.
TT_SOURCE_MASK	General mask defining the bits used for the source values.

Method

HTTP Method (POST, GET, etc.)

ReferrerURL

Get the referrer URL.

CurrentURL

The current URL of the Frame.

NewURL

By setting this argument you can alter the navigation URL programmatically.

Cancel

By setting this argument to True you can cancel the navigation.

Remarks

The event is fired on the UI thread before browser navigation of the main frame.

For performance reasons the event is disabled by default. Intercepting navigation in CEF requires the browser thread to be blocked until the OLE / COM event is handled, which subsequently requires switching to synchronous events model between the ActiveX and Chromium Embedded Framework sub-processes.

To enable synchronous events you must handle OnCreate event and set Settings.asynchronous_com_events = False.
To enable firing OnBeforeNavigate you must handle OnCreate event and set Settings.disable_on_before_navigate_event = False.
To enable the Cancel flag of the event also requires handling OnCreate and enabling it by setting Settings.allow_cancel_on_before_navigate = True.

Set Cancel to true to cancel the navigation or false to allow the navigation to proceed. You can also stop a URL navigation that has already started with StopLoading Method.

You can set a different URL to navigate to by setting the NewURL argument.

Example

Example (Visual Basic)

Option Explicit

Public URL As String

Private Sub Form_Load()
    URL = "https://www.webkitx.com/"
End Sub

Private Sub Form_Resize()
    On Error Resume Next
    WebKitX1.Move 0, 0, ScaleWidth, ScaleHeight
    Err.Clear
End Sub

Private Sub WebKitX1_OnCreate(ByVal Settings As WebKitXCEF3Lib.ISettings, CommandLineSwitches As String)
    Settings.asynchronous_com_events = False
    Settings.allow_cancel_on_before_navigate = True
    Settings.disable_on_before_navigate_event = False
End Sub

Private Sub WebKitX1_OnBrowserReady()
    WebKitX1.Open URL
End Sub

Private Sub WebKitX1_OnBeforeNavigate(ByVal ID As Long, ByVal BrowserID As Long, ByVal FrameID As Long, ByVal FrameName As String, ByVal IsRedirect As Boolean, ByVal ResourceType As WebKitXCEF3Lib.NAV_RESOURCE_TYPE, ByVal TransitionType As WebKitXCEF3Lib.NAV_TRANSITION_TYPE, ByVal Method As String, ByVal ReferrerURL As String, ByVal CurrentURL As String, NewURL As String, Cancel As Boolean)

    If NewURL = URL Then
        
        ' Ask the user what to do with the URL
        Dialog.Label1 = "Load URL?" + vbCrLf + NewURL
        Dialog.Show vbModal
        Cancel = Not Dialog.Result
        
    End If
    
    Unload Dialog

End Sub