The BLayout class provides an interface, and some basic implementation to manage the positioning and sizing of BLayoutItem s. More...

Inheritance diagram for BLayout:

Public Member Functions
	BLayout ()
	Default constructor.
	BLayout (BMessage *archive)
	Archive constructor.
virtual	~BLayout ()
	Destructor, deletes all BLayoutItem's that this layout manages, and detaches from this BLayout's owner view if there is one.
BLayout *	Layout () const
	Returns the BLayout this BLayoutItem resides in.
virtual status_t	Perform (perform_code d, void *arg)
	Perform some action (Internal method defined for binary compatibility purposes).
BView targeting and attachment information.
BView *	Owner () const
	Returns the Owner of this layout, i.e. the view this layout manages.
BView *	TargetView () const
	Returns the target view of this layout.
virtual BView *	View ()
	Returns the same BView* as BLayout::Owner(), this method is inherited from BLayoutItem.
Adding, removing, counting and accessing BLayout children
virtual BLayoutItem *	AddView (BView *child)
	Creates a BLayoutItem to represent a BView, and adds that item to this layout.
virtual BLayoutItem *	AddView (int32 index, BView *child)
	Creates a BLayoutItem to represent child, and adds that item at index to this layout. child is added to this BLayout's target view.
virtual bool	AddItem (BLayoutItem *item)
	Adds a BLayoutItem to this layout, and adds the BView it represents to this BLayout's target view.
virtual bool	AddItem (int32 index, BLayoutItem *item)
	Adds item to this layout, and adds the BView item represents to this BLayout's target view.
virtual bool	RemoveView (BView *child)
	Removes and deletes all BLayoutItem representing a BView from this layout.
virtual bool	RemoveItem (BLayoutItem *item)
	Removes a BLayoutItem from this layout, and also removes the view it represents from this BLayout's target view.
virtual BLayoutItem *	RemoveItem (int32 index)
	Remove the BLayoutItem at index.
BLayoutItem *	ItemAt (int32 index) const
	Get the BLayoutItem at index. Returns `NULL` if index is out of bounds.
int32	CountItems () const
	Get the number of BLayoutItem s in this layout.
int32	IndexOfItem (const BLayoutItem *item) const
	Get the index of a BLayoutItem in this layout.
int32	IndexOfView (BView *child) const
	Get the index of child in this layout.
Methods triggering or related to laying out this BLayout.
virtual void	Relayout (bool immediate=false)
	Request this BLayout to reposition and resize its items as required.
void	LayoutItems (bool force=false)
	If there is no layout currently ongoing, and force is `false`, creates a new BLayoutContext and calls the DoLayout() method of this BLayout and any BLayout s nested in this BLayout.
Reporting size and alignment constraints to a BLayout
virtual BSize	MinSize ()=0
	Returns the minimum desirable size for this item.
virtual BSize	MaxSize ()=0
	Returns the maximum desirable size for this item.
virtual BSize	PreferredSize ()=0
	Returns the preferred size for this item.
virtual BAlignment	Alignment ()=0
	Returns the requested alignment for this item.
virtual bool	HasHeightForWidth ()
	Returns whether or not this BLayoutItem's height constraints are dependent on its width.
virtual void	GetHeightForWidth (float width, float min, float max, float *preferred)
	Get this BLayoutItem's height constraints for a given width.
Overriding size constraints and alignment.
Although the explicit constraints placed on an item are not enforced by the BLayoutItem class, all Haiku BLayoutItem subclasses will use the BLayoutUtils::ComposeSize() or BLayoutUtils::ComposeAlignment() functions in when reporting these constraints. It is recommended that all subclasses do this as well, the BAbstractLayoutItem class provides any easy way to include this behaviour in your class.
virtual void	SetExplicitMinSize (BSize size)=0
	Set this item's explicit min size, to be used in MinSize().
virtual void	SetExplicitMaxSize (BSize size)=0
	Set this item's explicit max size, to be used in MaxSize().
virtual void	SetExplicitPreferredSize (BSize size)=0
	Set this item's explicit preferred size, to be used in PreferredSize().
virtual void	SetExplicitAlignment (BAlignment alignment)=0
	Set this item's explicit alignment, to be used in Alignment().
Getting and setting the visiblity of a BLayoutItem.
These methods take into account only the local visibility of this item, not the visibility of its ancestors.
virtual bool	IsVisible ()=0
	Return the current local visibility of this item. If an item is not visible, it will not be given space by the BLayout it resides in.
virtual void	SetVisible (bool visible)=0
	Set the local visibility of this item.
Getting and setting the current on-screen positioning of a BLayoutItem.
virtual BRect	Frame ()=0
	Return the bounding frame of this item.
virtual void	SetFrame (BRect frame)=0
	Set the bounding frame of this item.
void	AlignInFrame (BRect frame)
	Position this BLayoutItem within frame, given the value returned by Alignment(), and the size constraints for this item.
Utility methods for BLayout subclasses
Utility methods for the BLayout class to attach and retrieve arbitrary data for a BLayoutItem.
void *	LayoutData () const
	Retrieve arbitrary data attached to this BLayoutItem.
void	SetLayoutData (void *data)
	Attach arbitrary data to this BLayoutItem.
Static Public Member Functions
static BArchivable *	Instantiate (BMessage *archive)
	Static member to restore objects from messages.
Protected Member Functions
virtual status_t	AllArchived (BMessage *archive) const
	Method relating to the use of `BArchiver`.
virtual void	LayoutInvalidated (bool children)
	Hook called from InvalidateLayout().
BLayout Hook methods
virtual bool	ItemAdded (BLayoutItem *item, int32 atIndex)
	Hook method called when item is added to this layout.
virtual void	ItemRemoved (BLayoutItem *item, int32 fromIndex)
	Hook method called when item is removed from this layout.
virtual void	DoLayout ()=0
	Implemented by derived classes to position and resize the items in this layout.
virtual void	OwnerChanged (BView *was)
	Hook method called when this layout is attached to a BView.
virtual void	AttachedToLayout ()
	Hook method inherited from BLayoutItem, classes derived from BLayout must include the BLayout version of this method in their implementation.
virtual void	DetachedFromLayout (BLayout *layout)
	Hook method inherited from BLayoutItem, classes derived from BLayout must include the BLayout version of this method in their implementation.
virtual void	AncestorVisibilityChanged (bool shown)
	Hook method inherited from BLayoutItem, classes derived from BLayout must include the BLayout version of this method in their implementation.
Subclass helpers.
These methods are meant to ease the development of BLayout subclasses.
bool	AncestorsVisible () const
	Get the visibility of the ancestors of this layout.
BRect	LayoutArea ()
	Returns the on-screen area this layout has received to lay out its items in.
void	VisibilityChanged (bool show)
	Method to be called by derived classes in their SetVisible() implementation. Calls AncestorVisibilityChanged() on the items in this BLayout.
Invalidation and state mutators and accessors.
virtual void	InvalidateLayout (bool children=false)
	Invalidate this layout and any cached data this layout has relating to positioning and sizing of its items.
void	RequireLayout ()
	Flag this layout as stale, i.e. any cached data may still be valid, but the items need to be repositioned or resized.
bool	IsValid ()
	Returns whether this layout has been invalidated (via BLayout::InvalidateLayout()) and has not yet been validated (by doing a layout, or by its ResetLayoutInvalidation() method.
void	EnableLayoutInvalidation ()
	Re-enable layout invalidation after a call to DisableLayoutInvalidation().
void	DisableLayoutInvalidation ()
	Disable layout invalidation notifications, i.e. calls to this object's InvalidateLayout() method.
void	ResetLayoutInvalidation ()
	Reset layout invalidation, causing InvalidateLayout calls to proceed again. This method should be called once any cached data has been validated, or updated to valid values.
Archiving methods
These methods relate to the archiving or unarchiving of this object and the BLayoutItem's it contains
virtual status_t	Archive (BMessage *into, bool deep=true) const
	Archives this layout into archive. If deep is true, also archives the items in this layout, calling ItemArchived() for each one.
virtual status_t	AllUnarchived (const BMessage *from)
	Unarchives the BLayoutItem's for this layout, calling ItemUnarchived() for each one.
virtual status_t	ItemArchived (BMessage into, BLayoutItem item, int32 index) const
	Hook for derived classes to add data specific to item to the into BMessage. item resides at index.
virtual status_t	ItemUnarchived (const BMessage from, BLayoutItem item, int32 index)
	Hook for derived classes to retrieve data specific to item from the from BMessage. item resides at index.

Detailed Description

The BLayout class provides an interface, and some basic implementation to manage the positioning and sizing of BLayoutItem s.

BLayouts can be attached to a BView, managing the BLayoutItem's and BView's that reside in that view, or can be nested within another BLayout as a BLayoutItem.

Before adding a BLayoutItem to a BLayout, that layout must have a target view. When a BLayout is attached directly to a BView via BView::SetLayout() then that BView becomes the target of the layout. When a BLayout is nested in another BLayout (via BLayout::AddItem()) the nested BLayout inherits the target of the layout it's nested in, if it does not have a target already. You can retrieve the target view for a layout with the TargetView() method. When adding a BLayoutItem to a BLayout, the item's view (as returned by BLayoutItem::View()) is added to the BLayout's target view.

BView* topView = new BGroupView();
BLayout* topLayout = topView->GetLayout();

BLayout* nestedLayout = new BGroupLayout(B_HORIZONTAL);
topLayout->AddItem(nestedLayout);

BLayout* veryNestedLayout = new BGroupLayout(B_VERTICAL);
nestedLayout->AddItem(veryNestedLayout);

After executing this code, veryNestedLayout, nestedLayout, and topLayout all have the same target view: topView.

Continuing with the same objects...

BLayout* nestedLayoutWithView = (new BGroupView())->GetLayout();
topLayout->AddItem(nestedLayoutWithView);

nestedLayoutWithView does have a target view of topView. This is because nestedLayoutWithView is attached directly to a BView.

Warning:: This class is not yet finalized, if you use it in your software assume that it will break some time in the future.

Constructor & Destructor Documentation

BLayout::BLayout ( )

Default constructor.

After this constructor has finished, this BLayout holds no BLayoutItem's and does not have a target BView.

Warning:: Because a new BLayout does not have a target BView, calls to the AddItem() and AddView() will fail methods will fail.

BLayout::BLayout ( BMessage * archive )

Archive constructor.

Parameters:

archive The archive message.

BLayout::~BLayout ( ) [virtual]

Destructor, deletes all BLayoutItem's that this layout manages, and detaches from this BLayout's owner view if there is one.

Destructor method.

Each BLayoutItem's BView (as returned by BLayoutItem::View()) is also removed from their parent.

Note:: Because nested BLayout's are treated as BLayoutItem's, any layouts nested in this BLayout will be deleted.

Standard Destructor.

Member Function Documentation

bool BLayout::AddItem ( BLayoutItem * item ) [virtual]

Adds a BLayoutItem to this layout, and adds the BView it represents to this BLayout's target view.

Parameters:

item	The BLayoutItem to be added.

Return values:

true	success
false	failure

Reimplemented in BGridLayout, and BGroupLayout.

bool BLayout::AddItem	(	int32	index,
		BLayoutItem *	item
	)		`[virtual]`

Adds item to this layout, and adds the BView item represents to this BLayout's target view.

Parameters:

item	The BLayoutItem to be added.
index	The index at which to add `item`.

If index is out of bounds, item will be added at the end. If index is somewhere between the first and last indices, then items from index to the end will be shuffled over by one.

Return values:

true	success
false	failure

Reimplemented in BGridLayout, and BGroupLayout.

BLayoutItem * BLayout::AddView ( BView * child ) [virtual]

Creates a BLayoutItem to represent a BView, and adds that item to this layout.

child is added to this BLayout's target view.

Returns:: The BLayoutItem created to represent child is, or NULL if there was an error.

Parameters:

child The BView to be added to this BLayout.

Reimplemented in BGridLayout, and BGroupLayout.

BAlignment BLayoutItem::Alignment ( ) [pure virtual, inherited]

Returns the requested alignment for this item.

The value returned from this method is used in BLayoutItem::AlignInFrame(), which BLayouts use to position and resize items. In a vertical BGroupLayout, for example, although each item recieves the same horizontal area, each item can use that area differently, aligning to the left, right or center for example.

Implemented in BAbstractLayout.

virtual status_t BLayout::AllArchived ( BMessage * into ) const [protected, virtual]

Method relating to the use of BArchiver.

This hook function is called once the first BArchiver that was created in an archiving session is either destroyed, or has its Finish() method called. Implementations of this method can be used, in conjunction with BArchiver::IsArchived(), to reference objects in your archive that you do not own, depending on whether or not those objects were archived by their owners. Implementations of this method should call the implementation of their parent class, the same as for the Archive() method.

Warning:: To guarantee that your AllArchived() method will be called during archival, you must create a BArchiver object in your Archive() implementation.; You should archive any objects you own in your Archive() method implementation, and NOT your AllArchived() method.

See also:: BArchiver BArchiver::Finish()

Reimplemented from BLayoutItem.

Reimplemented in BGridLayout, BTwoDimensionalLayout, BAbstractLayout, and BGroupLayout.

bool BLayout::AncestorsVisible ( ) const

Get the visibility of the ancestors of this layout.

If a BLayout is connected to a BView, this will always return true. If a BLayout is nested in another layout (it was passed to AddItem()), then this will reflect the visibility of this BLayout's parent layout. If any layout is hidden (by BLayout::SetVisible()) between this layout and its target BView's layout, then this method will return false.

void BLayout::DetachedFromLayout ( BLayout * layout ) [protected, virtual]

Hook method inherited from BLayoutItem, classes derived from BLayout must include the BLayout version of this method in their implementation.

Parameters:

layout The BLayout that this BLayout was detached from.

Reimplemented from BLayoutItem.

Reimplemented in BAbstractLayout.

BRect BLayoutItem::Frame ( ) [pure virtual, inherited]

Return the bounding frame of this item.

The returned BRect is in the coordinate system of the target view of the BLayout this item belongs to.

Implemented in BAbstractLayout.

void BLayoutItem::GetHeightForWidth	(	float	width,
		float *	min,
		float *	max,
		float *	preferred
	)		`[virtual, inherited]`

Get this BLayoutItem's height constraints for a given width.

If a BLayoutItem does not have height for width constraints (HasHeightForWidth() returns false) it does not need to implement this method.

Note:: It is prudent to compare min, max, preferred to NULL before dereferencing them.

Reimplemented in BTwoDimensionalLayout.

bool BLayoutItem::HasHeightForWidth ( ) [virtual, inherited]

Returns whether or not this BLayoutItem's height constraints are dependent on its width.

Note:: By default, this method returns false.

Reimplemented in BTwoDimensionalLayout.

int32 BLayout::IndexOfItem ( const BLayoutItem * item ) const

Get the index of a BLayoutItem in this layout.

Parameters:

item	The BLayoutItem whose index you want.

Return values:

-1	item was not found in this BLayout.

int32 BLayout::IndexOfView ( BView * child ) const

Get the index of child in this layout.

Note:: This finds the index of views added through BLayout::AddView(), not the index of an item which represents child that was added through BLayout::AddItem().

static BArchivable * BArchivable::Instantiate ( BMessage * archive ) [static, inherited]

Static member to restore objects from messages.

You should always check that the archive argument actually corresponds to your class. The automatic functions, such as instantiate_object() and BUnarchiver::InstantiateObject() will not choose the wrong class but manual calls to this member might be faulty. You can verify that archive stores an object of your calss with the validate_instantiation() function.

Parameters:

archive The message with the data of the object to restore.

Return values:

You	should return a pointer to the object you create with `archive`, or `NULL` if unarchival fails.

Warning:: The default implementation will always return NULL. Even though it is possible to store plain BArchivable objects, it is impossible to restore them.

See also:: instantiate_object(BMessage *from); BUnarchiver::InstantiateObject()

Reimplemented in BView, BCollator, BDirectWindow, BTextView, BBitmap, BGridLayout, BCursor, BAlert, BListView, BApplication, BLooper, BGroupLayout, BHandler, BColorControl, BDragger, BControl, BBox, BButton, BScrollView, and BCheckBox.

void BLayout::InvalidateLayout ( bool children = false ) [virtual]

Invalidate this layout and any cached data this layout has relating to positioning and sizing of its items.

Invalidating a BLayout also invalidates the view it is connected to (if there is one) and the BLayout this layout (or this BLayout's view) resides in.

Although this method is virtual, you should not override it, override the BLayout::LayoutInvalidated() hook instead.

This method should be called whenever the layout becomes invalid. This might happen if the size constraints of an item in this layout change, this layout is given more or less space than it previously had, or an object in this layout has had its InvalidateLayout() method called.

See also:: BView::InvalidateLayout(), BLayoutItem::InvalidateLayout(), BLayout::LayoutInvalidated()

Reimplemented from BLayoutItem.

bool BLayoutItem::IsVisible ( ) [pure virtual, inherited]

Return the current local visibility of this item. If an item is not visible, it will not be given space by the BLayout it resides in.

A simple implementation would return the last thing passed to SetVisible(). A more complex implementation may deal with a BView that could be hidden in any number of ways.

Implemented in BAbstractLayout.

bool BLayout::ItemAdded	(	BLayoutItem *	item,
		int32	atIndex
	)		`[protected, virtual]`

Hook method called when item is added to this layout.

Parameters:

item	The BLayoutItem that is being added.
atIndex	The index of the BLayoutItem.

Return values:

true	success
false	failure, item will not be added.

Note:: This is a good time to allocate data for a BLayoutItem and attach it to item via BLayoutItem::SetLayoutData().

Reimplemented in BGridLayout, BAbstractLayout, and BGroupLayout.

status_t BLayout::ItemArchived	(	BMessage *	into,
		BLayoutItem *	item,
		int32	index
	)		const `[protected, virtual]`

Hook for derived classes to add data specific to item to the into BMessage. item resides at index.

Note:: The same archive is passed to BLayout::ItemArchived() for all items, so any data added for each item will be stored in an array.

Reimplemented in BGridLayout, BTwoDimensionalLayout, BAbstractLayout, and BGroupLayout.

void BLayout::ItemRemoved	(	BLayoutItem *	item,
		int32	fromIndex
	)		`[protected, virtual]`

Hook method called when item is removed from this layout.

Parameters:

item	The BLayoutItem being removed.
fromIndex	The index where item used to reside.

When this hook is called, item is not yet completely removed. It can no longer be accessed with LayoutItemAt(), nor does it contribute to the value of CountItems(), but the item has not yet had its ItemDetached() hook called.

Note:: This is a good time to delete the data you've attached to item via BLayoutItem::SetLayoutData().

Reimplemented in BGridLayout, BAbstractLayout, and BGroupLayout.

status_t BLayout::ItemUnarchived	(	const BMessage *	from,
		BLayoutItem *	item,
		int32	index
	)		`[protected, virtual]`

Hook for derived classes to retrieve data specific to item from the from BMessage. item resides at index.

Note:: The same archive is passed to BLayout::ItemArchived() for all items, so any data added for each item will be stored in an array. You should pass index to the BMessage methods you will be using in this method.

Reimplemented in BGridLayout, BTwoDimensionalLayout, BAbstractLayout, and BGroupLayout.

BRect BLayout::LayoutArea ( )

Returns the on-screen area this layout has received to lay out its items in.

The return value is in the coordinate space of this BLayout's target view. If this BLayout is attached directly to a BView, then LayoutArea().LeftTop() == B_ORIGIN .

void * BLayoutItem::LayoutData ( ) const [inherited]

Retrieve arbitrary data attached to this BLayoutItem.

Note:: This method should only be called by a BLayout subclass.

virtual void BLayout::LayoutInvalidated ( bool children ) [protected, virtual]

Hook called from InvalidateLayout().

Override this method to clean out an cached layout info. It is good practice to recreate such info only on demand, eg when MinSize() or friends are called.

If children is true, then you should invalidate any information on child objects as well, and propagate the invalidation to them.

Reimplemented from BLayoutItem.

Reimplemented in BTwoDimensionalLayout, and BAbstractLayout.

void BLayout::LayoutItems ( bool force = false )

If there is no layout currently ongoing, and force is false, creates a new BLayoutContext and calls the DoLayout() method of this BLayout and any BLayout s nested in this BLayout.

This method also guarantees that the owner view of this layout (as returned by BLayout::Owner()) performs a layout as well (if it is suitable to do so).

Parameters:

force Force the LayoutItems.

void BLayout::OwnerChanged ( BView * was ) [protected, virtual]

Hook method called when this layout is attached to a BView.

Parameters:

was	The previous owner of this BLayout, for new BLayout s, this will be `NULL`.

Reimplemented in BAbstractLayout.

void BLayout::Relayout ( bool immediate = false ) [virtual]

Request this BLayout to reposition and resize its items as required.

If immediate is false, and there is already a request to have the window this layout resides in re-laid-out, then the layout will happen at that time. If immediate is true, and there is no such pending request, nor is this BLayout's parent layout in the process of laying out its items, then this BLayout will now layout its items.

Parameters:

immediate Whether or not to Relayout immediately or wait for pending requests first.

Reimplemented from BLayoutItem.

bool BLayout::RemoveItem ( BLayoutItem * item ) [virtual]

Removes a BLayoutItem from this layout, and also removes the view it represents from this BLayout's target view.

Parameters:

item	The BLayoutItem to be removed

Warning:: item is not deleted, you must delete it manually, or add it to another BLayout.; item->View(), even when it is removed from the target view, is not deleted. If you want it deleted, you must delete it yourself!

Return values:

true	success
false	failure

BLayoutItem * BLayout::RemoveItem ( int32 index ) [virtual]

Remove the BLayoutItem at index.

See also:: RemoveItem(BLayoutItem*)

Returns:: The BLayoutItem that was removed.

bool BLayout::RemoveView ( BView * child ) [virtual]

Removes and deletes all BLayoutItem representing a BView from this layout.

Parameters:

child The BView to be removed.

Return values:

true	success
false	failure

void BLayoutItem::SetFrame ( BRect frame ) [pure virtual, inherited]

Set the bounding frame of this item.

frame is in the coordinate system of the target view of the BLayout that this item belongs to.

Implemented in BTwoDimensionalLayout, and BAbstractLayout.

void BLayoutItem::SetLayoutData ( void * data ) [inherited]

Attach arbitrary data to this BLayoutItem.

Note:: This method should only be called by a BLayout subclass.

BView * BLayout::TargetView ( ) const

Returns the target view of this layout.

The target view of a layout becomes the parent of any BView's in this layout, as well as the BView's returned by BLayoutItem::View() for each BLayoutItem in this layout.

void BLayout::VisibilityChanged ( bool show ) [protected]

Method to be called by derived classes in their SetVisible() implementation. Calls AncestorVisibilityChanged() on the items in this BLayout.

Parameters:

show	`true` to show, `false` to hide.

Public Member Functions

Static Public Member Functions

Protected Member Functions

Subclass helpers.

Invalidation and state mutators and accessors.

Archiving methods

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation