LayoutItem.dox

/*
 * Copyright 2010, Haiku, Inc. All Rights Reserved.
 * Distributed under the terms of the MIT License.
 *
 * Documentation by:
 *   Alex Wilson <yourpalal2@gmail.com>
 * Corresponds to:
 *   /trunk/headers/os/interface/LayoutItem.h  rev 38207
 *   /trunk/src/kits/interface/LayoutItem.cpp  rev 38207
 */


/*!
	\file LayoutItem.h
	\brief Describes the BLayoutItem class
*/


/*!
	\class BLayoutItem
	\ingroup interface
	\ingroup layout
	\ingroup libbe

	\brief Abstract class representing things that are positionable and
		resizable by objects of the BLayout class.

	The BLayoutItem class provides an interface that is meant to be used almost
	exclusively by objects of the BLayout class. Despite this, there are some
	methods that are provided for other users of the class.

	\warning This class is not yet finalized, if you use it in your software
	assume that it will break some time in the future.
*/


/*!
	\fn BLayoutItem::BLayoutItem(BMessage* archive)
	\brief Archive constructor.

	Creates a BLayoutItem from the \a archive message.
*/


/*!
	\fn BLayout* BLayoutItem::Layout() const
	\brief Returns the BLayout this BLayoutItem resides in.
*/


/*!
	\fn BLayout::~BLayout()
	\brief Destructor method.

	Standard Destructor.
*/


/*!
	\name Reporting size and alignment constraints to a BLayout
*/


//! @{


/*!
	\fn BSize BLayoutItem::MinSize() = 0
	\brief Returns the minimum desirable size for this item.
*/


/*!
	\fn BSize BLayoutItem::MaxSize() = 0
	\brief Returns the maximum desirable size for this item.
*/


/*!
	\fn BSize BLayoutItem::PreferredSize() = 0
	\brief Returns the preferred size for this item.
*/


/*!
	\fn BAlignment BLayoutItem::Alignment() = 0
	\brief 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.
*/


/*!
	\fn bool BLayoutItem::HasHeightForWidth()
	\brief Returns whether or not this BLayoutItem&apos;s height constraints are
		dependent on its width.
	
	\note By default, this method returns \c false.
*/


/*!
	\fn void BLayoutItem::GetHeightForWidth(float width, float* min,
		float* max, float* preferred)
	\brief Get this BLayoutItem&apos;s height constraints for a given \a width.

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

	\note It is prudent to compare \a min, \a max, \a preferred to \c NULL
	before dereferencing them.
*/


//! @}


/*!
	\name 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.
*/


//! @{


/*!
	\fn void BLayoutItem::SetExplicitMinSize(BSize size) = 0
	\brief Set this item's explicit min size, to be used in MinSize().
*/


/*!
	\fn void BLayoutItem::SetExplicitMaxSize(BSize size) = 0
	\brief Set this item's explicit max size, to be used in MaxSize().
*/


/*!
	\fn void BLayoutItem::SetExplicitPreferredSize(BSize size) = 0
	\brief Set this item's explicit preferred size, to be used in
		PreferredSize().
*/


/*!
	\fn void BLayoutItem::SetExplicitAlignment(BAlignment alignment) = 0
	\brief Set this item's explicit alignment, to be used in Alignment().
*/


//! @}


/*!
	\name 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. \n
*/


//! @{


/*!
	\fn bool BLayoutItem::IsVisible() = 0
	\brief 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.
*/


/*!
	\fn void BLayoutItem::SetVisible(bool visible) = 0
	\brief Set the local visibility of this item.
*/


//! @}


/*!
	\name Getting and setting the current on-screen positioning of a BLayoutItem.
*/


//! @{


/*!
	\fn void BLayoutItem::AlignInFrame(BRect frame)
	\brief Position this BLayoutItem within \a frame, given the value returned
		by Alignment(), and the size constraints for this item.
*/


/*!
	\fn BRect BLayoutItem::Frame() = 0
	\brief 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.
*/


/*!
	\fn void BLayoutItem::SetFrame(BRect frame) = 0
	\brief Set the bounding frame of this item.

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


//! @}


/*!
	\fn BView* BLayoutItem::View()
	\brief Return the BView this item is representing, or \c NULL if it does not
		represent any view.

	When a BLayoutItem is added to a BLayout, this method is called, and the
	returned BView will be added to the BLayout&apos;s target view.
*/


/*!
	\name Layout events and requests.

	\brief These methods represent events or requests originating from a
	BLayout. In some implementations they may be handled directly by this
	BLayoutItem, but many implementations will forward these events to
	another object.
*/


//! @{


/*!
	\fn void BLayoutItem::InvalidateLayout(bool children = false)
	\brief Invalidate the layout of this item, or the object it represents.
	\param children Whether or not to invalidate children of this object.

	Although this method is virtual, you should not override it in your classes,
	override LayoutInvalidated() instead. This method will take care of calling
	the InvalidateLayout() methods of affected views/layouts/items. However, if
	there is an object that is somehow connected to this one by means other than
	the standard mechanisms provided by the Haiku API, you should use
	the LayoutInvalidated() hook to do this.
*/


/*!
	\fn void BLayoutItem::Relayout(bool immediate = false)
	\brief Relayout any children or onscreen data this item contains. Often
		this request is forwarded to another object.

	The default implementation of this method will likely be sufficient in
	most cases. Assuming \c this->View() doesn't return \c NULL, the default
	implementation calls Relayout() or Layout() on the value returned
	by View().
*/


//! @}


/*!
	\name Utility methods for BLayout subclasses
	\brief Utility methods for the BLayout class to attach and retrieve
		arbitrary data for a BLayoutItem.
*/


//! @{


/*!
	\fn void* BLayoutItem::LayoutData() const
	\brief Retrieve arbitrary data attached to this BLayoutItem.

	\note This method should only be called by a BLayout subclass.
*/


/*!
	\fn void BLayoutItem::SetLayoutData(void* data)
	\brief Attach arbitrary data to this BLayoutItem.

	\note This method should only be called by a BLayout subclass.
*/


//! @}


/*!
	\name Hook methods
*/


//! @{


/*!
	\fn void BLayoutItem::LayoutInvalidated(bool children)
	\brief 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 \a children is \c true, then you should invalidate any information on
	child objects as well, and propagate the invalidation to them.
*/


/*!
	\fn void BLayoutItem::AttachedToLayout()
	\brief Hook called when this object is attached to a BLayout (via
		BLayout::AddItem())

	\note You can find the BLayout you've been attached to with the Layout()
		method.
*/


/*!
	\fn void BLayoutItem::DetachedFromLayout(BLayout* layout)
	\brief Hook called when this object is attached to a BLayout (via
		BLayout::RemoveItem())

	\warning You should not use this hook to reattach \c this to \a BLayout,
		doing so will cause undefined behaviour (probably a crash).

	\param layout The BLayout you were previously attached to.
*/


/*!
	\fn void BLayoutItem::AncestorVisibilityChanged(bool shown)
	\brief Hook called when this BLayoutItem&apos;s ancestors change visibility,
		effectively hiding or showing this item.

	Implementations of this method should alter the onscreen visibility of this
	item. I.E. if \a shown is \c false, nothing should be drawn to represent
	this item.

	\note This method should not effect the value returned by this object's
		IsVisible() method.

	\param shown \c true to show, \c false to hide.
*/


//! @}