10. Container Widgets

10.1 The EventBox

Some GTK widgets don't have associated X windows, so they just draw on their parents. Because of this, they cannot receive events and if they are incorrectly sized, they don't clip so you can get messy overwriting, etc. If you require more from these widgets, the EventBox is for you.

At first glance, the EventBox widget might appear to be totally useless. It draws nothing on the screen and responds to no events. However, it does serve a function - it provides an X window for its child widget. This is important as many GTK widgets do not have an associated X window. Not having an X window saves memory and improves performance, but also has some drawbacks. A widget without an X window cannot receive events, and does not perform any clipping on its contents. Although the name EventBox emphasizes the event-handling function, the widget can also be used for clipping. (and more, see the example below).

To create a new EventBox widget, use:

A child widget can then be added to this EventBox:

The following example demonstrates both uses of an EventBox - a label is created that is clipped to a small box, and set up so that a mouse-click on the label causes the program to exit. Resizing the window reveals varying amounts of the label. If you want to see what the fancy mouse-over hand looks like you'll have to compile and run the program yourself.

10.2 The Alignment Widget

The alignment widget allows you to place a widget within its window at a position and size relative to the size of the Alignment widget itself. For example, it can be very useful for centering a widget within the window.

There is just one function and one procedure associated with the Alignment widget:

The function creates a new Alignment widget with the specified parameters. The procedure allows the alignment parameters of an exisiting Alignment widget to be altered.

All four alignment parameters are floating point numbers which can range from 0.0 to 1.0. The xalign and yalign arguments affect the position of the widget placed within the Alignment widget. The xscale and yscale arguments effect the amount of space allocated to the widget.

A child widget can be added to this Alignment widget using:

For an example of using an Alignment widget, refer to the example for the Progress Bar widget.

10.3 Fixed Container

The Fixed container allows you to place widgets at a fixed position within it's window, relative to it's upper left hand corner. The position of the widgets can be changed dynamically.

There are only two procedures and one function associated with the fixed widget:

The function gtk_fixed_new() allows you to create a new Fixed container.

gtk_fixed_put() places widget in the container fixed at the position specified by x and y.

gtk_fixed_move() allows the specified widget to be moved to a new position.

The following example illustrates how to use the Fixed Container. Clicking on any of the buttons marked Press me will move the button according to the move_button() procedure defined in the program.

10.4 Layout Container

The Layout container is similar to the Fixed container except that it implements an infinite (where infinity is less than 2^32) scrolling area. The X window system has a limitation where windows can be at most 32767 pixels wide or tall. The Layout container gets around this limitation by doing some exotic stuff using window and bit gravities, so that you can have smooth scrolling even when you have many child widgets in your scrolling area.

A Layout container is created using:

As you can see, you can optionally specify the Adjustment objects that the Layout widget will use for its scrolling.

You can add and move widgets in the Layout container using the following two procedures:

The size of the Layout container can be set using the next procedure:

Layout containers are one of the very few widgets in the GTK widget set that actively repaint themselves on screen as they are changed using the above functions (the vast majority of widgets queue requests which are then processed when control returns to the gtk_main() function).

When you want to make a large number of changes to a Layout container, you can use the following two procedures to disable and re-enable this repainting functionality:

The final two functions and two procedures for use with Layout widgets are for manipulating the horizontal and vertical adjustment widgets:

10.5 Frames

Frames can be used to enclose one or a group of widgets with a box which can optionally be labelled. The position of the label and the style of the box can be altered to suit.

A Frame can be created with the following function:

The label is by default placed in the upper left hand corner of the frame. A value of NIL for the label argument will result in no label being displayed. The text of the label can be changed using the next procedure.

The position of the label can be changed using this procedure:

xalign and yalign take values between 0.0 and 1.0. xalign indicates the position of the label along the top horizontal of the frame. yalign is not currently used. The default value of xalign is 0.0 which places the label at the left hand end of the frame.

The next procedure alters the style of the box that is used to outline the frame.

The type argument can take one of the following values:

*the default

The following code example illustrates the use of the Frame widget.

10.6 Aspect Frames

The aspect frame widget is like a frame widget, except that it also enforces the aspect ratio (that is, the ratio of the width to the height) of the child widget to have a certain value, adding extra space if necessary. This is useful, for instance, if you want to preview a larger image. The size of the preview should vary when the user resizes the window, but the aspect ratio needs to always match the original image.

To create a new aspect frame use:

xalign and yalign specify alignment as with Alignment widgets. If obey_child is TRUE, the aspect ratio of a child widget will match the aspect ratio of the ideal size it requests. Otherwise, it is given by ratio.

To change the options of an existing aspect frame, you can use:

As an example, the following program uses an AspectFrame to present a drawing area whose aspect ratio will always be 2:1, no matter how the user resizes the top-level window.

10.7 Paned Window Widgets

The paned window widgets are useful when you want to divide an area into two parts, with the relative size of the two parts controlled by the user. A groove is drawn between the two portions with a handle that the user can drag to change the ratio. The division can either be horizontal (hpaned) or vertical (vpaned).

To create a new paned window, call one of:

After creating the paned window widget, you need to add child widgets to its two halves. To do this, use the procedures:

gtk_paned_add1() adds the child widget to the left or top half of the paned window. gtk_paned_add2() adds the child widget to the right or bottom half of the paned window.

A paned widget can be changed visually using the following two procedures:

The first of these sets the size of the handle and the second sets the size of the gutter that is between the two parts of the paned window.

As an example, we will create part of the user interface of an imaginary e-mail program. A window is divided into two portions vertically, with the top portion being a list of e-mail messages and the bottom portion the text of the e-mail message. Most of the program is pretty straightforward. A couple of points to note:

• text can't be added to a Text widget until it is realized. This could be done by calling gtk_widget_realize(), but as a demonstration of an alternate technique, we connect a handler to the realize signal to add the text.
• Also, we need to add the GTK_SHRINK option to some of the items in the table containing the text window and its scrollbars, so that when the bottom portion is made smaller, the correct portions shrink instead of being pushed off the bottom of the window.

10.8 Viewports

It is unlikely that you will ever need to use the Viewport widget directly. You are much more likely to use the Scrolled Window widget which itself uses the Viewport.

A viewport widget allows you to place a larger widget within it such that you can view a part of it at a time. It uses Adjustments to define the area that is currently in view.

A Viewport is created with the function

As you can see you can specify the horizontal and vertical Adjustments that the widget is to use when you create the widget. It will create its own if you pass NIL as the value of the arguments.

You can get and set the adjustments after the widget has been created using these functions and procedures:

The only other viewport procedure is used to alter its appearance:

Possible values for the type parameter are:

10.9 Scrolled Windows

Scrolled windows are used to create a scrollable area with another widget inside it. You may insert any type of widget into a scrolled window, and it will be accessible regardless of the size by using the scrollbars.

The following function is used to create a new scrolled window.

Where the first argument is the adjustment for the horizontal direction, and the second, the adjustment for the vertical direction. These are almost always set to NIL.

This sets the policy to be used with respect to the scrollbars. The first argument is the scrolled window you wish to change. The second sets the policy for the horizontal scrollbar, and the third the policy for the vertical scrollbar.

The policy may be one of GTK_POLICY_AUTOMATIC or GTK_POLICY_ALWAYS. GTK_POLICY_AUTOMATIC will automatically decide whether you need scrollbars, whereas GTK_POLICY_ALWAYS will always leave the scrollbars there.

You can then place your object into the scrolled window using the following procedure:

Here is a simple example that packs a table eith 100 toggle buttons into a scrolled window. I've only commented on the parts that may be new to you.

Try playing with resizing the window. You'll notice how the scrollbars react. You may also wish to use the gtk_widget_set_usize() call to set the default size of the window or other widgets.

10.10 Button Boxes

Button Boxes are a convenient way to quickly layout a group of buttons. They come in both horizontal and vertical flavours. You create a new Button Box with one of the following calls, which create a horizontal or vertical box, respectively:

The only attributes pertaining to button boxes effect how the buttons are laid out. You can change the spacing between the buttons with:

Similarly, the current spacing values can be queried using:

The second attribute that we can access effects the layout of the buttons within the box. It is set using one of:

The layout argument can take one of the following values:

The current layout setting can be retrieved using:

Buttons are added to a Button Box using the usual procedure:

Here's an example that illustrates all the different layout settings for Button Boxes.

10.11 Toolbar

Toolbars are usually used to group some number of widgets in order to simplify customization of their look and layout. Typically a toolbar consists of buttons with icons, labels and tooltips, but any other widget can also be put inside a toolbar. Finally, items can be arranged horizontally or vertically and buttons can be displayed with icons, labels, or both.

Creating a toolbar is (as one may already suspect) done with the following function:

where orientation may be one of:

and style one of:

The style applies to all the buttons created with the item functions (not to buttons inserted into toolbar as separate widgets).

After creating a toolbar one can append, prepend and insert items (that means simple text strings) or elements (that means any widget types) into the toolbar. To describe an item we need a label text, a tooltip text, a private tooltip text, an icon for the button and a callback function for it. For example, to append or prepend an item you may use the following functions:

If you want to use gtk_toolbar_insert_item(), the only additional parameter which must be specified is the position in which the item should be inserted, thus:

To simplify adding spaces between toolbar items, you may use the following procedures:

While the size of the added space can be set globally for a whole toolbar with the procedure:

If it's required, the orientation of a toolbar and its style can be changed on the fly using the following procedures:

Where orientation is one of GTK_ORIENTATION_HORIZONTAL or GTK_ORIENTATION_VERTICAL. The style is used to set appearance of the toolbar items by using one of GTK_TOOLBAR_ICONS, GTK_TOOLBAR_TEXT, or GTK_TOOLBAR_BOTH.

To show some other things that can be done with a toolbar, let's take the following program (we'll interrupt the listing with some additional explanations). To start off though, it might be useful to see what we're aiming at. In order to see the different tooltips you'll need to compile and run the program yourself, but this is what the rest of it looks like:

The above beginning seems for sure familiar to you if it's not your first GTK program. There is one additional thing though, we include a nice XPM picture to serve as an icon for all of the buttons.

In fact not all of the above widgets are needed here, but to make things clearer I put them all together.

The above are just two callbacks that will be called when one of the buttons on a toolbar is pressed. You should already be familiar with things like this if you've already used toggle buttons (and radio buttons).

The above should be similar to any other GTK application. Just initialization of GTK, creating the window, etc. There is only one thing that probably needs some explanation: a handle box. A handle box is just another box that can be used to pack widgets in to. The difference between it and typical boxes is that it can be detached from a parent window (or, in fact, the handle box remains in the parent, but it is reduced to a very small rectangle, while all of its contents are re-parented to a new freely floating window). It is usually nice to have a detachable toolbar, so these two widgets occur together quite often.

Well, what we do above is just a straightforward initialization of the toolbar widget and creation of a GDK pixmap with its mask. If you want to know something more about using pixmaps, refer to GDK documentation or to the Pixmaps section earlier in this tutorial.

In the above code you see the simplest case: adding a button to toolbar. Just before appending a new item, we have to construct a pixmap widget to serve as an icon for this item; this step will have to be repeated for each new item. Just after the item we also add a space, so the following items will not touch each other. As you see gtk_toolbar_append_item() returns a pointer to our newly created button widget, so that we can work with it in the normal way.

Here we begin creating a radio buttons group. To do this we use gtk_toolbar_append_element(). In fact, using this function one can also add simple items or even spaces (type = GTK_TOOLBAR_CHILD_SPACE or GTK_TOOLBAR_CHILD_BUTTON). In the above case we start creating a radio group. In creating other radio buttons for this group a pointer to the previous button in the group is required, so that a list of buttons can be easily constructed (see the section on Radio Buttons earlier in this tutorial).

In the end we have to set the state of one of the buttons manually (otherwise they all stay in active state, preventing us from switching between them).

A toggle button can be created in the obvious way (if one knows how to create radio buttons already).

As you see, adding any kind of widget to a toolbar is simple. The one thing you have to remember is that this widget must be shown manually (contrary to other items which will be shown together with the toolbar).

10.12 Notebooks

The NoteBook Widget is a collection of pages that overlap each other, each page contains different information with only one page visible at a time. This widget has become more common lately in GUI programming, and it is a good way to show blocks of similar information that warrant separation in their display.

The first function call you will need to know, as you can probably guess by now, is used to create a new notebook widget.

Once the notebook has been created, there are a number of functions that operate on the notebook widget. Let's look at them individually.

The first one we will look at is how to position the page indicators. These page indicators or tabs as they are referred to, can be positioned in four ways: top, bottom, left, or right.

position will be one of the following, which are pretty self explanatory:

GTK_POS_TOP is the default.

Next we will look at how to add pages to the notebook. There are three ways to add pages to the NoteBook. Let's look at the first two together as they are quite similar.

These functions add pages to the notebook by inserting them from the back of the notebook (append), or the front of the notebook (prepend). child is the widget that is placed within the notebook page, and tab_label is the label for the page being added. The child widget must be created separately, and is typically a set of options setup witin one of the other container widgets, such as a table.

The final function for adding a page to the notebook contains all of the properties of the previous two, but it allows you to specify what position you want the page to be in the notebook.

The parameters are the same as _append_ and _prepend_ except for the extra parameter, position. This parameter is used to specify what place this page will be inserted into the first page having position zero.

Now that we know how to add a page, lets see how we can remove a page from the notebook.

This procedure takes the page specified by page_num and removes it from the widget pointed to by notebook.

To find out what the current page is in a notebook use the function:

These next two procedures are simple calls to move the notebook page forward or backward. Simply provide the respective procedure call with the notebook widget you wish to operate on. Note: When the NoteBook is currently on the last page, and gtk_notebook_next_page() is called, the notebook will wrap back to the first page. Likewise, if the NoteBook is on the first page, and gtk_notebook_prev_page() is called, the notebook will wrap to the last page.

This next procedure sets the active page. If you wish the notebook to be opened to page 5 for example, you would use this procedure. Without using this procedure, the notebook defaults to the first page.

The next two procedures add or remove the notebook page tabs and the notebook border respectively.

The next function is useful when the you have a large number of pages, and the tabs don't fit on the page. It allows the tabs to be scrolled through using two arrow buttons.

show_tabs, show_border and scrollable can be either TRUE or FALSE.

Now let's look at an example, it is expanded from the testgtk.c code that comes with the GTK distribution. This small program creates a window with a notebook and six buttons. The notebook contains 11 pages, added in three different ways, appended, inserted, and prepended. The buttons allow you rotate the tab positions, add/remove the tabs and border, remove a page, change pages in both a forward and backward manner, and exit the program.

I hope this helps you on your way with creating notebooks for your GTK applications.