/** Copyright 2010 Haiku, Inc. All rights reserved.* Distributed under the terms of the MIT License.** Authors:* Alex Wilson, yourpalal2@gmail.com** Corresponds to:* headers/os/interface/LayoutItem.h rev 49040* src/kits/interface/LayoutItem.cpp rev 49040*//*!\file LayoutItem.h\ingroup layout\ingroup libbe\brief Describes the BLayoutItem class.*//*!\class BLayoutItem\ingroup layout\ingroup libbe\brief Abstract class representing things that are positionable andresizable by objects of the BLayout class.The BLayoutItem class provides an interface that is meant to be used almostexclusively by objects of the BLayout class. Despite this, there are somemethods that are provided for other users of the class.\warning This class is not yet finalized, if you use it in your softwareassume that it will break some time in the future.\since Haiku R1*//*!\fn BLayoutItem::BLayoutItem(BMessage* archive)\brief Archive constructor.Creates a BLayoutItem from the \a archive message.\since Haiku R1*//*!\fn BLayout* BLayoutItem::Layout() const\brief Returns the BLayout this BLayoutItem resides in.\since Haiku R1*//*!\fn bool BLayoutItem::RemoveSelf()\brief Remove this layout item from the BLayout it is a part of.This method works analoguous to BView::RemoveSelf(), that is it removesitself from the parent layout and returns whether or not this wassuccesful.\return \c true if the item was removed from the layout, or \c false ifitem was not part of a layout, or removal was succesful.\since Haiku R1*//*!\fn BLayout::~BLayout()\brief Destructor method.Standard Destructor.\since Haiku R1*//*!\name Reporting Size and Alignment Constraints to a BLayout*///! @{/*!\fn BSize BLayoutItem::MinSize() = 0\brief Returns the minimum desirable size for this item.\since Haiku R1*//*!\fn BSize BLayoutItem::MaxSize() = 0\brief Returns the maximum desirable size for this item.\since Haiku R1*//*!\fn BSize BLayoutItem::PreferredSize() = 0\brief Returns the preferred size for this item.\since Haiku R1*//*!\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 itemcan use that area differently, aligning to the left, right or center forexample.\since Haiku R1*//*!\fn bool BLayoutItem::HasHeightForWidth()\brief Returns whether or not this BLayoutItem's height constraints aredependent on its width.\note By default, this method returns \c false.\since Haiku R1*//*!\fn void BLayoutItem::GetHeightForWidth(float width, float* min,float* max, float* preferred)\brief Get this BLayoutItem'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 thismethod.\note It is prudent to compare \a min, \a max, \a preferred to \c NULLbefore dereferencing them.\since Haiku R1*///! @}/*!\name Overriding Size and Alignment ConstraintsAlthough the explicit constraints placed on an item are not enforced by theBLayoutItem class, all Haiku BLayoutItem subclasses will use theBLayoutUtils::ComposeSize() or BLayoutUtils::ComposeAlignment() functionsin when reporting these constraints. It is recommended that all subclassesdo this as well, the BAbstractLayoutItem class provides any easy way toinclude this behaviour in your class.\since Haiku R1*///! @{/*!\fn void BLayoutItem::SetExplicitMinSize(BSize size) = 0\brief Set this item's explicit min size, to be used in MinSize().This forces the minimal size for the item and overrides any constraintsthat would normally be used to compute it. Most importantly, the minimalsize of children is ignored, so setting this can lead to the children notfitting the view.\since Haiku R1*//*!\fn void BLayoutItem::SetExplicitMaxSize(BSize size) = 0\brief Set this item's explicit max size, to be used in MaxSize().\since Haiku R1*//*!\fn void BLayoutItem::SetExplicitPreferredSize(BSize size) = 0\brief Set this item's explicit preferred size, to be used inPreferredSize().\since Haiku R1*//*!\fn void BLayoutItem::SetExplicitSize(BSize size)\brief Set the explicity size to \a size.This method is a convenience method that sets the minimum size, maximumsize and preferred size to \a size, as to force this layout item to havea specific size.\param size The specific (non-zero) size for this layout item.\since Haiku R1*//*!\fn void BLayoutItem::SetExplicitAlignment(BAlignment alignment) = 0\brief Set this item's explicit alignment, to be used in Alignment().\since Haiku R1*///! @}/*!\name Getting/Setting the Visibility of a BLayoutItemThese methods take into account only the local visibility of thisitem, 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 notvisible, 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 couldbe hidden in any number of ways.\since Haiku R1*//*!\fn void BLayoutItem::SetVisible(bool visible) = 0\brief Set the local visibility of this item.\since Haiku R1*///! @}/*!\name Getting/Setting Current On-Screen Positioning of a BLayoutItem*///! @{/*!\fn void BLayoutItem::AlignInFrame(BRect frame)\brief Position this BLayoutItem within \a frame, given the value returnedby Alignment(), and the size constraints for this item.\since Haiku R1*//*!\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 theBLayout this item belongs to.\since Haiku R1*//*!\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 BLayoutthat this item belongs to.\since Haiku R1*///! @}/*!\fn BView* BLayoutItem::View()\brief Return the BView this item is representing, or \c NULL if it does notrepresent any view.When a BLayoutItem is added to a BLayout, this method is called, and thereturned BView will be added to the BLayout's target view.\since Haiku R1*//*!\name Layout Events and RequestsThese methods represent events or requests originating from aBLayout. In some implementations they may be handled directly by thisBLayoutItem, but many implementations will forward these events toanother object.*///! @{/*!\fn void BLayoutItem::InvalidateLayout(bool children = false)\brief Invalidate the layout of this item, or the object it represents.Although this method is virtual, you should not override it in your classes,override LayoutInvalidated() instead. This method will take care of callingthe InvalidateLayout() methods of affected views/layouts/items. However, ifthere is an object that is somehow connected to this one by means other thanthe standard mechanisms provided by the Haiku API, you should usethe LayoutInvalidated() hook to do this.\param children Whether or not to invalidate children of this object.\since Haiku R1*//*!\fn void BLayoutItem::Relayout(bool immediate = false)\brief Relayout any children or onscreen data this item contains. Oftenthis request is forwarded to another object.The default implementation of this method will likely be sufficient inmost cases. Assuming \c this->View() doesn't return \c NULL, the defaultimplementation calls Relayout() or Layout() on the value returnedby View().\since Haiku R1*///! @}/*!\name Utility Methods for BLayout SubclassesUtility methods for the BLayout class to attach and retrievearbitrary 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.\since Haiku R1*//*!\fn void BLayoutItem::SetLayoutData(void* data)\brief Attach arbitrary data to this BLayoutItem.\note This method should only be called by a BLayout subclass.\since Haiku R1*///! @}/*!\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 goodpractice to recreate such info only on demand, eg when MinSize() or friendsare called.If \a children is \c true, then you should invalidate any information onchild objects as well, and propagate the invalidation to them.\since Haiku R1*//*!\fn void BLayoutItem::AttachedToLayout()\brief Hook called when this object is attached to a BLayout (viaBLayout::AddItem())\note You can find the BLayout you've been attached to with the Layout()method.\since Haiku R1*//*!\fn void BLayoutItem::DetachedFromLayout(BLayout* layout)\brief Hook called when this object is attached to a BLayout (viaBLayout::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.\since Haiku R1*//*!\fn void BLayoutItem::AncestorVisibilityChanged(bool shown)\brief Hook called when this BLayoutItem's ancestors change visibility,effectively hiding or showing this item.Implementations of this method should alter the onscreen visibility of thisitem. I.E. if \a shown is \c false, nothing should be drawn to representthis item.\note This method should not effect the value returned by this object'sIsVisible() method.\param shown \c true to show, \c false to hide.\since Haiku R1*///! @}