CefApp
在cefsimple中，提到了一個cefapp的型別，這個型別是一個介面類，主要目的是提供獲取三種handler的介面
///
// Implement this interface to provide handler implementations. Methods will be
// called by the process and/or thread indicated.
///
/*--cef(source=client,no_debugct_check)--*/
class CefApp : public virtual CefBaseRefCounted {
public:
///
// Provides an opportunity to view and/or modify command-line arguments before
// processing by CEF and Chromium. The |process_type| value will be empty for
// the browser process. Do not keep a reference to the CefCommandLine object
// passed to this method. The CefSettings.command_line_args_disabled value
// can be used to start with an empty command-line object. Any values
// specified in CefSettings that equate to command-line arguments will be set
// before this method is called. Be cautious when using this method to modify
// command-line arguments for non-browser processes as this may result in
// undefined behavior including crashes.
///
/*--cef(optional_param=process_type)--*/
virtual void OnBeforeCommandLineProcessing(
const CefString& process_type,
CefRefPtr<CefCommandLine> command_line) {}
///
// Provides an opportunity to register custom schemes. Do not keep a reference
// to the |registrar| object. This method is called on the main thread for
// each process and the registered schemes should be the same across all
// processes.
///
/*--cef()--*/
virtual void OnRegisterCustomSchemes(
CefRawPtr<CefSchemeRegistrar> registrar) {}
///
// Return the handler for resource bundle events. If
// CefSettings.pack_loading_disabled is true a handler must be returned. If no
// handler is returned resources will be loaded from pack files. This method
// is called by the browser and render processes on multiple threads.
///
/*--cef()--*/
virtual CefRefPtr<CefResourceBundleHandler> GetResourceBundleHandler() {
return NULL;
}
///
// Return the handler for functionality specific to the browser process. This
// method is called on multiple threads in the browser process.
///
/*--cef()--*/
virtual CefRefPtr<CefBrowserProcessHandler> GetBrowserProcessHandler() {
return NULL;
}
///
// Return the handler for functionality specific to the render process. This
// method is called on the render process main thread.
///
/*--cef()--*/
virtual CefRefPtr<CefRenderProcessHandler> GetRenderProcessHandler() {
return NULL;
}
};
GetResourceBundleHandler``GetBrowserProcessHandler``GetRenderProcessHandler分別可以得到對應回呼handler，如果繼承了這三種handler就能在這些時機處理自己的回呼業務，舉個例子，例如CefBrowserProcessHandler，可以實作browser行程的回呼，用于執行browser行程生命周期中的重要回呼，
///
// Class used to implement browser process callbacks. The methods of this class
// will be called on the browser process main thread unless otherwise indicated.
///
/*--cef(source=client,no_debugct_check)--*/
class CefBrowserProcessHandler : public virtual CefBaseRefCounted {
public:
///
// Called on the browser process UI thread immediately after the CEF context
// has been initialized.
///
/*--cef()--*/
virtual void OnContextInitialized() {}
///
// Called before a child process is launched. Will be called on the browser
// process UI thread when launching a render process and on the browser
// process IO thread when launching a GPU or plugin process. Provides an
// opportunity to modify the child process command line. Do not keep a
// reference to |command_line| outside of this method.
///
/*--cef()--*/
virtual void OnBeforeChildProcessLaunch(
CefRefPtr<CefCommandLine> command_line) {}
///
// Called on the browser process IO thread after the main thread has been
// created for a new render process. Provides an opportunity to specify extra
// information that will be passed to
// CefRenderProcessHandler::OnRenderThreadCreated() in the render process. Do
// not keep a reference to |extra_info| outside of this method.
///
/*--cef()--*/
virtual void OnRenderProcessThreadCreated(
CefRefPtr<CefListValue> extra_info) {}
///
// Return the handler for printing on Linux. If a print handler is not
// provided then printing will not be supported on the Linux platform.
///
/*--cef()--*/
virtual CefRefPtr<CefPrintHandler> GetPrintHandler() { return NULL; }
///
// Called from any thread when work has been scheduled for the browser process
// main (UI) thread. This callback is used in combination with CefSettings.
// external_message_pump and CefDoMessageLoopWork() in cases where the CEF
// message loop must be integrated into an existing application message loop
// (see additional comments and warnings on CefDoMessageLoopWork). This
// callback should schedule a CefDoMessageLoopWork() call to happen on the
// main (UI) thread. |delay_ms| is the requested delay in milliseconds. If
// |delay_ms| is <= 0 then the call should happen reasonably soon. If
// |delay_ms| is > 0 then the call should be scheduled to happen after the
// specified delay and any currently pending scheduled call should be
// cancelled.
///
/*--cef()--*/
virtual void OnScheduleMessagePumpWork(int64 delay_ms) {}
};
上述代碼就是CefBrowserProcessHandler提供的介面，可以看到，當背景關系初始化后，子行程啟動前等等時機都有，在cefsimple中，還用OnContextInitialized函式來CreateBrowser，是十分重要的handler，
結合cefsimple來看，cefapp的具體作用，
// Implement application-level callbacks for the browser process.
class SimpleApp : public CefApp, public CefBrowserProcessHandler {
public:
SimpleApp();
// CefApp methods:
virtual CefRefPtr<CefBrowserProcessHandler> GetBrowserProcessHandler()
OVERRIDE {
return this;
}
// CefBrowserProcessHandler methods:
virtual void OnContextInitialized() OVERRIDE;
private:
// Include the default reference counting implementation.
IMPLEMENT_REFCOUNTING(SimpleApp);
};
十分簡單，還將CefApp和CefBrowserProcessHandler多繼承了，并且在OnContextInitialized中，呼叫了CreateBrowser，
從cefclient和cefsimple這倆demo來看，在構建app的時候CefApp主要用在倆地方，CefExecuteProcess和CefInitialize，從上面的代碼可以看出CefApp和監視行程級別的handler一起作業所以需要的時機會比較早，
CefClient
與CefApp相對應的還有CefClient，這個CefClient指的是一個類，不是指的那個demo程式，和CefClient類似，他也是提供了很多獲取handler的介面
class CefClient : public virtual CefBaseRefCounted {
public:
///
// Return the handler for context menus. If no handler is provided the default
// implementation will be used.
///
/*--cef()--*/
virtual CefRefPtr<CefContextMenuHandler> GetContextMenuHandler() {
return NULL;
}
///
// Return the handler for dialogs. If no handler is provided the default
// implementation will be used.
///
/*--cef()--*/
virtual CefRefPtr<CefDialogHandler> GetDialogHandler() { return NULL; }
///
// Return the handler for browser display state events.
///
/*--cef()--*/
virtual CefRefPtr<CefDisplayHandler> GetDisplayHandler() { return NULL; }
...
這些handler的都是基于功能的回呼，應用開發者應該提供對應的handler實作，然后提供CefClient獲取對應handler物體，
因為是基于功能的回呼，所以在瀏覽器沒起來的時候，也沒有啥功能，因此CefClient初始化和傳入的時機會比CefApp要晚一些，會在CreateBrowser的時候傳入，
在cefsimple中，也是采用了多繼承的方式實作，因為很簡單
class SimpleHandler : public CefClient,
public CefDisplayHandler,
public CefLifeSpanHandler,
public CefLoadHandler {
public:
explicit SimpleHandler(bool use_views);
~SimpleHandler();
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