/* * Copyright 2010 Haiku, Inc. All rights reserved. * Distributed under the terms of the MIT License. * * Authors: * Alex Wilson, yourpalal2@gmail.com */ /*! \page layout_intro Introducing the Layout API. Haiku's Layout API is centered around the BLayoutItem and BLayout classes. The BLayoutItem class represents thing that can be managed by a BLayout, which is itself a BLayoutItem. Before we go any further, it is a good idea to familiarize yourself with the different BLayout classes available in Haiku: \li BGroupLayout \li BGridLayout \li BCardLayout \li BSplitView You'll notice that BSplitView is not actually a BLayout, but a BView. The BSplitView class uses a custom BLayout behind the scenes, but because it must also be able to draw, a BView is required. Other BLayout objects have BView objects that can be used for convenience. \li BGroupLayout : BGroupView \li BGridLayout : BGridView \li BCardLayout : BTabView (also provides on-screen tabs) Although it is not necessary to use these classes to make use of the corresponding layouts, it does make things easier. Once you have an understanding of what each BLayout does, you can start designing an interface with them. Let's consider a very simple window, with a single item in the center. For this, any of the layouts mentioned above would work, but we'll use a BGroupLayout, because it suits this purpose the best. So, let's review the BGroupLayout constructor: \code BGroupLayout(enum orientation orientation, float spacing = B_USE_DEFAULT_SPACING) \endcode Because we only have one item in this layout, \c orientation and \c spacing become irrelevant. Let's choose B_VERTICAL for \c orientation, and leave \c spacing at its default. \code BGroupLayout* group = new BGroupLayout(B_VERTICAL); BWindow* window = MakeWindow(); window->SetLayout(group); \endcode Before we can add anything to our layout, we must attach it to something, and here we've used the BWindow::SetLayout() method to accomplish that. By doing this, \c window takes ownership of \c group, so there is no need to manually delete group when we're done with it. Now that we've got our BGroupLayout in place, we can start adding things to it, let's add a BStringView. \code group->AddView(MakeStringView("Haiku rocks!")); \endcode That does it! Now we've got a BWindow with a horizontal BGroupLayout holding a single BView. However, if we want to ensure that our BStringView is always centered in the window, we should give it an explicit BAlignment. So the last line becomes: \code BLayoutItem* stringView = group->AddView(MakeStringView("Haiku rocks!")); stringView->SetExplicitAlignment(BAlignment(B_ALIGN_HORIZONTAL_CENTER, B_ALIGN_VERTICAL_CENTER); \endcode Now our BStringView will always be right in the middle of the space allotted to it, which at the moment is the whole of \c window. Now let's take things one step further, and add a BMenuBar into the mix. \code group->AddView(0, MakeMenuBar()); group->SetInsets(0, 0, 0, 0); \endcode Because we want our BMenuBar to appear at the very top of the window, we have to insert it at index \c 0, above the BStringView we added earlier. We also use BTwoDimensionalLayout::SetInsets() to make sure that our BMenuBar is flush to the edges of \c window. We also want a bit of space between our BMenuBar and our BStringView, but \c group's spacing has already been set by the BGroupLayout constructor, so we don't need to do that. Now that we've put our BGroupLayout to good use, we can rest easy, assured that GUI will always look nice, no matter what font is used, or how big or little \c window is stretched. Of course, very few interfaces are as simple as this one. Luckily, the layout classes can deal with complex layouts. Suppose, for example, that we wanted to add a grid of BButtons under our BStringView. We could use a BGridLayout for this. Let's review the BGridLayout constructor: \code BGridLayout(float horizontal = B_USE_DEFAULT_SPACING, float vertical = B_USE_DEFAULT_SPACING); \endcode Because we want a bit of breathing room between our buttons, we'll leave vertical and horizontal spacing as is. \code BGridLayout* grid = new BGridLayout(); group->AddItem(grid); \endcode You'll notice that we've added \c grid directly to \c group. This means that any BView objects we add to \c grid will become children of \c window, but will be positioned by \c grid. \code grid->AddView(MakeSmallButton(), 0, 0); grid->AddView(MakeSmallButton(), 1, 0); grid->AddView(MakeBigButton(), 0, 1, 2, 1); grid->AddView(MakeSmallButton(), 1, 2); \endcode Now we've got a nice grid of BButton objects, let's go over it quickly: \li \c grid has two columns and three rows. \li The cells (0, 0), (1, 0), and (1, 2) hold small buttons \li The cells (0, 1) and (1, 1) hold a single button that spans both cells. \li The cell (0, 2) is empty. How easy was that? Very easy! One of the features you'll find incredibly handy in the layout API is the builders in LayoutBuilder.h. Here's how our whole layout would look if it were done with these builders: \code BLayoutBuilder::Group<>(window, B_VERTICAL) .SetInsets(0, 0, 0, 0) .Add(MakeMenuBar()) .Add(MakeStringView("Haiku rocks!")) .AddGrid() .Add(MakeSmallButton(), 0, 0) .Add(MakeSmallButton(), 1, 0) .Add(MakeBigButton(), 0, 1, 2, 1) .Add(MakeSmallButton(), 1, 2); \endcode This is only one way that you could build this layout, but it is probably the most succinct. Functionally, this is equivalent to all the previous code in this introduction. */