In the Client BWindow_InitData function after getting the reply from the app server. There is the task for the view creation.

void
BWindow::_InitData(BRect frame, const char* title, window_look look,
	window_feel feel, uint32 flags,	uint32 workspace, int32 bitmapToken)
{
	STRACE(("BWindow::InitData()\n"));

	if (be_app == NULL) {
		debugger("You need a valid BApplication object before interacting with "
			"the app_server");
		return;
	}

	frame.left = roundf(frame.left);
	frame.top = roundf(frame.top);
	frame.right = roundf(frame.right);
	frame.bottom = roundf(frame.bottom);

	fFrame = frame;

	if (title == NULL)
		title = "";

	fTitle = strdup(title);

	_SetName(title);

	fFeel = feel;
	fLook = look;
	fFlags = flags | B_ASYNCHRONOUS_CONTROLS;

	fInTransaction = bitmapToken >= 0;
	fUpdateRequested = false;
	fActive = false;
	fShowLevel = 1;

	fTopView = NULL;
	fFocus = NULL;
	fLastMouseMovedView	= NULL;
	fKeyMenuBar = NULL;
	fDefaultButton = NULL;

	// Shortcut 'Q' is handled in _HandleKeyDown() directly, as its message
	// get sent to the application, and not one of our handlers.
	// It is only installed for non-modal windows, though.
	fNoQuitShortcut = IsModal();

	if ((fFlags & B_NOT_CLOSABLE) == 0 && !IsModal()) {
		// Modal windows default to non-closable, but you can add the
		// shortcut manually, if a different behaviour is wanted
		AddShortcut('W', B_COMMAND_KEY, new BMessage(B_QUIT_REQUESTED));
	}

	// Edit modifier keys

	AddShortcut('X', B_COMMAND_KEY, new BMessage(B_CUT), NULL);
	AddShortcut('C', B_COMMAND_KEY, new BMessage(B_COPY), NULL);
	AddShortcut('V', B_COMMAND_KEY, new BMessage(B_PASTE), NULL);
	AddShortcut('A', B_COMMAND_KEY, new BMessage(B_SELECT_ALL), NULL);

	// Window modifier keys

	AddShortcut('M', B_COMMAND_KEY | B_CONTROL_KEY,
		new BMessage(_MINIMIZE_), NULL);
	AddShortcut('Z', B_COMMAND_KEY | B_CONTROL_KEY,
		new BMessage(_ZOOM_), NULL);
	AddShortcut('Z', B_SHIFT_KEY | B_COMMAND_KEY | B_CONTROL_KEY,
		new BMessage(_ZOOM_), NULL);
	AddShortcut('H', B_COMMAND_KEY | B_CONTROL_KEY,
		new BMessage(B_HIDE_APPLICATION), NULL);
	AddShortcut('F', B_COMMAND_KEY | B_CONTROL_KEY,
		new BMessage(_SEND_TO_FRONT_), NULL);
	AddShortcut('B', B_COMMAND_KEY | B_CONTROL_KEY,
		new BMessage(_SEND_BEHIND_), NULL);

	// We set the default pulse rate, but we don't start the pulse
	fPulseRate = 500000;
	fPulseRunner = NULL;

	fIsFilePanel = false;

	fMenuSem = -1;

	fMinimized = false;

	fMaxZoomHeight = 32768.0;
	fMaxZoomWidth = 32768.0;
	fMinHeight = 0.0;
	fMinWidth = 0.0;
	fMaxHeight = 32768.0;
	fMaxWidth = 32768.0;

	fLastViewToken = B_NULL_TOKEN;

	// TODO: other initializations!
	fOffscreen = false;

	// Create the server-side window

	port_id receivePort = create_port(B_LOOPER_PORT_DEFAULT_CAPACITY,
		"w<app_server");
	if (receivePort < B_OK) {
		// TODO: huh?
		debugger("Could not create BWindow's receive port, used for "
				 "interacting with the app_server!");
		delete this;
		return;
	}

	STRACE(("BWindow::InitData(): contacting app_server...\n"));

	// let app_server know that a window has been created.
	fLink = new(std::nothrow) BPrivate::PortLink(
		BApplication::Private::ServerLink()->SenderPort(), receivePort);
	if (fLink == NULL) {
		// Zombie!
		return;
	}

	{
		BPrivate::AppServerLink lockLink;
			// we're talking to the server application using our own
			// communication channel (fLink) - we better make sure no one
			// interferes by locking that channel (which AppServerLink does
			// implicetly)

		if (bitmapToken < 0) {
			fLink->StartMessage(AS_CREATE_WINDOW);
		} else {
			fLink->StartMessage(AS_CREATE_OFFSCREEN_WINDOW);
			fLink->Attach<int32>(bitmapToken);
			fOffscreen = true;
		}

		fLink->Attach<BRect>(fFrame);
		fLink->Attach<uint32>((uint32)fLook);
		fLink->Attach<uint32>((uint32)fFeel);
		fLink->Attach<uint32>(fFlags);
		fLink->Attach<uint32>(workspace);
		fLink->Attach<int32>(_get_object_token_(this));
		fLink->Attach<port_id>(receivePort);
		fLink->Attach<port_id>(fMsgPort);
		fLink->AttachString(title);

		port_id sendPort;
		int32 code;
		if (fLink->FlushWithReply(code) == B_OK
			&& code == B_OK
			&& fLink->Read<port_id>(&sendPort) == B_OK) {
			// read the frame size and its limits that were really
			// enforced on the server side

			fLink->Read<BRect>(&fFrame);
			fLink->Read<float>(&fMinWidth);
			fLink->Read<float>(&fMaxWidth);
			fLink->Read<float>(&fMinHeight);
			fLink->Read<float>(&fMaxHeight);

			fMaxZoomWidth = fMaxWidth;
			fMaxZoomHeight = fMaxHeight;
		} else
			sendPort = -1;

		// Redirect our link to the new window connection
		fLink->SetSenderPort(sendPort);
		STRACE(("Server says that our send port is %ld\n", sendPort));
	}

	STRACE(("Window locked?: %s\n", IsLocked() ? "True" : "False"));

	_CreateTopView();
}

In the last chapter we have explored all the function of this snippet but _CreateTopView() is left. Now it's time to explore this one.

#1 _CreateTopView()

This function is defined at: src/kits/interface/Window.cpp

void
BWindow::_CreateTopView()
{
	STRACE(("_CreateTopView(): enter\n"));

	BRect frame = fFrame.OffsetToCopy(B_ORIGIN);
	// TODO: what to do here about std::nothrow?
	fTopView = new BView(frame, "fTopView", B_FOLLOW_ALL, B_WILL_DRAW);
	fTopView->fTopLevelView = true;

	//inhibit check_lock()
	fLastViewToken = _get_object_token_(fTopView);

	// set fTopView's owner, add it to window's eligible handler list
	// and also set its next handler to be this window.

	STRACE(("Calling setowner fTopView = %p this = %p.\n",
		fTopView, this));

	fTopView->_SetOwner(this);

	// we can't use AddChild() because this is the top view
	fTopView->_CreateSelf();
	STRACE(("BuildTopView ended\n"));
}

In the _CreateTopView function of the BWindow class, a top-level BView is created and initialized. Here's what happens in this function:

	BRect frame = fFrame.OffsetToCopy(B_ORIGIN);

• It creates a BRect named frame by copying the window's frame and offsetting it to the origin (0,0).

	fTopView = new BView(frame, "fTopView", B_FOLLOW_ALL, B_WILL_DRAW);

• It creates a new BView named fTopView using the frame calculated earlier. The view is given the name "fTopView", follows all resizing of its parent, and will draw its content.

	fTopView->fTopLevelView = true;

• It sets the fTopLevelView member variable of the fTopView to true. This likely indicates that this view is the top-level view within the window.

//inhibit check_lock()
	fLastViewToken = _get_object_token_(fTopView);

• It inhibits the check for locks on the view by setting the fLastViewToken member variable to the object token of fTopView.

	fTopView->_SetOwner(this);

• It sets the owner of fTopView to the window itself by calling _SetOwner(this) on fTopView. This associates the window with the view.

	fTopView->_CreateSelf();

• It then calls _CreateSelf() on fTopView to initialize the view. This function likely performs internal setup and initialization for the view.

#2 BView(BRect frame, const char* name, uint32 resizingMode, uint32 flags) Constructor

This constructor is defined at: src/kits/interface/View.cpp

BView::BView(BRect frame, const char* name, uint32 resizingMode, uint32 flags)
	:
	BHandler(name)
{
	_InitData(frame, name, resizingMode, flags);
}

The constructor BView::BView initializes a BView object with the provided parameters. Here's what it does:

• It calls the constructor of the base class BHandler with the provided name, initializing the handler part of the BView.
• It then calls the _InitData function with the provided frame, name, resizing mode, and flags. This function initializes the data members of the BView object.

#3 _InitData(BRect frame, const char* name, uint32 resizingMode, uint32 flags)

This function is defined at: src/kits/interface/View.cpp

void
BView::_InitData(BRect frame, const char* name, uint32 resizingMode,
	uint32 flags)
{
	// Info: The name of the view is set by BHandler constructor

	STRACE(("BView::_InitData: enter\n"));

	// initialize members
	if ((resizingMode & ~_RESIZE_MASK_) || (flags & _RESIZE_MASK_))
		printf("%s BView::_InitData(): resizing mode or flags swapped\n", name);

	// There are applications that swap the resize mask and the flags in the
	// BView constructor. This does not cause problems under BeOS as it just
	// ors the two fields to one 32bit flag.
	// For now we do the same but print the above warning message.
	// TODO: this should be removed at some point and the original
	// version restored:
	// fFlags = (resizingMode & _RESIZE_MASK_) | (flags & ~_RESIZE_MASK_);
	fFlags = resizingMode | flags;

	// handle rounding
	frame.left = roundf(frame.left);
	frame.top = roundf(frame.top);
	frame.right = roundf(frame.right);
	frame.bottom = roundf(frame.bottom);

	fParentOffset.Set(frame.left, frame.top);

	fOwner = NULL;
	fParent = NULL;
	fNextSibling = NULL;
	fPreviousSibling = NULL;
	fFirstChild = NULL;

	fShowLevel = 0;
	fTopLevelView = false;

	fCurrentPicture = NULL;
	fCommArray = NULL;

	fVerScroller = NULL;
	fHorScroller = NULL;

	fIsPrinting = false;
	fAttached = false;

	// TODO: Since we cannot communicate failure, we don't use std::nothrow here
	// TODO: Maybe we could auto-delete those views on AddChild() instead?
	fState = new BPrivate::ViewState;

	fBounds = frame.OffsetToCopy(B_ORIGIN);
	fShelf = NULL;

	fEventMask = 0;
	fEventOptions = 0;
	fMouseEventOptions = 0;

	fLayoutData = new LayoutData;

	fToolTip = NULL;

	if ((flags & B_SUPPORTS_LAYOUT) != 0) {
		SetViewUIColor(B_PANEL_BACKGROUND_COLOR);
		SetLowUIColor(ViewUIColor());
		SetHighUIColor(B_PANEL_TEXT_COLOR);
	}
}

	fFlags = resizingMode | flags;

• It combines the resizing mode and flags to set the view's flags.

// handle rounding
	frame.left = roundf(frame.left);
	frame.top = roundf(frame.top);
	frame.right = roundf(frame.right);
	frame.bottom = roundf(frame.bottom);

• It rounds the coordinates of the frame to integer values using the roundf function.

#4 _CreateSelf()

This function is defined at: src/kits/interface/View.cpp

bool
BView::_CreateSelf()
{
	// AS_VIEW_CREATE & AS_VIEW_CREATE_ROOT do not use the
	// current view mechanism via _CheckLockAndSwitchCurrent() - the token
	// of the view and its parent are both send to the server.

	if (fTopLevelView)
		fOwner->fLink->StartMessage(AS_VIEW_CREATE_ROOT);
	else
 		fOwner->fLink->StartMessage(AS_VIEW_CREATE);

	fOwner->fLink->Attach<int32>(_get_object_token_(this));
	fOwner->fLink->AttachString(Name());
	fOwner->fLink->Attach<BRect>(Frame());
	fOwner->fLink->Attach<BPoint>(LeftTop());
	fOwner->fLink->Attach<uint32>(ResizingMode());
	fOwner->fLink->Attach<uint32>(fEventMask);
	fOwner->fLink->Attach<uint32>(fEventOptions);
	fOwner->fLink->Attach<uint32>(Flags());
	fOwner->fLink->Attach<bool>(IsHidden(this));
	fOwner->fLink->Attach<rgb_color>(fState->view_color);
	if (fTopLevelView)
		fOwner->fLink->Attach<int32>(B_NULL_TOKEN);
	else
		fOwner->fLink->Attach<int32>(_get_object_token_(fParent));
	fOwner->fLink->Flush();

	_CheckOwnerLockAndSwitchCurrent();
	fState->UpdateServerState(*fOwner->fLink);

	// we create all its children, too

	for (BView* child = fFirstChild; child != NULL;
			child = child->fNextSibling) {
		child->_CreateSelf();
	}

	fOwner->fLink->Flush();
	return true;
}

Determining Creation Type:

• The function distinguishes between creating a top-level view (fTopLevelView) and creating a regular view.
• For top-level view, a special message (AS_VIEW_CREATE_ROOT) is sent to the server. Otherwise, the standard AS_VIEW_CREATE message is used.

Preparing Message:

• The function starts constructing the message to create the view by using the appropriate message type (AS_VIEW_CREATE_ROOT or AS_VIEW_CREATE).
• It attaches various parameters to the message, including:
  • Token of the view: Identifies the view uniquely.
  • Name of the view.
  • Frame: Defines the position and size of the view.
  • Position (Left-Top): Specifies the top-left corner of the view within its parent's coordinate system.
  • Resizing mode: Determines how the view behaves when its parent is resized.
  • Event mask: Specifies which types of events the view should receive.
  • Event options: Additional options related to event handling.
  • Flags: Various flags indicating properties and behavior of the view.
  • Visibility: Indicates whether the view is hidden.
  • View color: Specifies the color of the view.
  • Token of the parent view: Identifies the parent view of the current view.

Sending Message:

• The constructed message, along with all attached parameters, is sent to the server via the owner's message link (fOwner->fLink).
• This communication with the server initializes the view's representation on the screen.

Updating Server State:

• After sending the creation message, the function updates the server-side state of the view based on any changes that occurred during creation.
• This ensures that the server's representation of the view is synchronized with the client-side representation.

Creating Children:

• The function iterates over all child views of the current view (fFirstChild) and recursively calls _CreateSelf() for each child.
• This process ensures that all child views are also created and properly initialized.

Finalizing Message:

• Once all child views are created, another flush operation is performed on the message link to ensure all pending messages are sent to the server.

Returning Success:

• Finally, the function returns true to indicate that the view creation process was successful.