6 The Button Widget

6.1 Normal Buttons

We've almost seen all there is to see of the button widget. It's pretty simple. There are however two ways to create a button. You can use the gtk_button_new_with_label() function to create a button with a label, or use gtk_button_new() function to create a blank button. It's then up to you to pack a label or pixmap into this new button. To do this, create a new box, and then pack your objects into this box using the usual gtk_box_pack_start(), and then use gtk_container_add() to pack the box into the button.

Here's an example of using gtk_button_new() to create a button with a picture and a label in it. I've broken up the code to create a box from the rest so you can use it in your programs. There are further examples of using pixmaps later in the tutorial. If you'd like to compile and run the following code you'll need to copy the the pixmap info.xpm from /usr/doc/fpc-1.0.6/examples/gtk/tutorial (assuming you've installed the fpc documentation) to the directory that the program is situated in.

The xpm_label_box function could be used to pack xpm's and labels into any widget that can be a container.

Notice in xpm_label_box how there is a call to gtk_widget_get_style(). Every widget has a style, consisting of foreground and background colours for a variety of situations, font selection, and other graphics data relevant to a widget. These style values are defaulted in each widget, and are required by many GDK function calls, such as gdk_pixmap_create_from_xpm(), which here is given the normal background colour. The style data of widgets may be customized, using GTK's rc files.

Also notice the call to gtk_widget_realize() after setting the window's border width. This function uses GDK to create the X windows related to the widget. The function is automatically called when you invoke gtk_widget_show() for a widget, and so has not been shown in earlier examples. But the call to gdk_pixmap_create_from_xpm() requires that its window argument refer to a real X window, so it is necessary to realize the widget before this GDK call.

The button widget has the following signals:

6.2 Toggle Buttons

Toggle buttons are derived from normal buttons and are very similar, except they will always be in one of two states, alternated by a click. They may be depressed, and when you click again, they will pop back up. Click again, and they will pop back down.

Toggle buttons are the basis for check buttons and radio buttons, as such, many of the calls used for toggle buttons are inherited by radio and check buttons. I will point these out when we come to them. Creating a new toggle button:

As you can imagine, these work identically to the normal button widget calls. The first creates a blank toggle button, and the second, a button with a label widget already packed into it.

To retrieve the state of the toggle widget, including radio and check buttons, we use a construct as shown in our example below. This tests the state of the toggle, by accessing the active field of the toggle widget's structure, after first using the GTK_TOGGLE_BUTTON macro to cast the widget pointer into a toggle widget pointer. The signal of interest to us emitted by toggle buttons (the toggle button, check button, and radio button widgets) is the toggled signal. To check the state of these buttons, set up a signal handler to catch the toggled signal, and access the structure to determine its state. The callback will look something like:

To force the state of a toggle button, and its children, the radio and check buttons, use this function:

The above call can be used to set the state of the toggle button, and its children the radio and check buttons. Passing in your created button as the first argument, and a TRUE or FALSE for the second state argument to specify whether it should be down (depressed) or up (released). Default is up, or FALSE.

Note that when you use the gtk_toggle_button_set_active() function, and the state is actually changed, it causes the clicked signal to be emitted from the button.

This simply toggles the button, and emits the toggled signal.

6.3 Check Buttons

Check buttons inherit many properties and functions from the the toggle buttons above, but look a little different. Rather than being buttons with text inside them, they are small squares with the text to the right of them. These are often used for toggling options on and off in applications.

The two creation functions are similar to those of the normal button.

The *_new_with_label() function creates a check button with a label beside it. Checking the state of the check button is identical to that of the toggle button. 423 92

Here's an example to illustrate (you don't get this is the C tutorial!):

6.4 Radio Buttons

Radio buttons are similar to check buttons except they are grouped so that only one may be selected/depressed at a time. This is good for places in your application where you need to select from a short list of options.

Creating a new radio button is done with one of these procedures:

You'll notice the extra argument to these calls. They require a group to perform their duty properly. The first call to gtk_radio_button_new_with_label() or gtk_radio_button_new_with_label() should pass NIL as the first argument. Then create a group using:

The important thing to remember is that gtk_radio_button_group() must be called for each new button added to the group, with the previous button passed in as an argument. The result is then passed into the next call to gtk_radio_button_new() or gtk_radio_button_new_with_label(). This allows a chain of buttons to be established. The example below should make this clear.

You can shorten this slightly by using the following syntax, which removes the need for a variable to hold the list of buttons. This form is used in the example to create the third button:

It is also a good idea to explicitly set which button should be the default depressed button with:

This is described in the section on toggle buttons, and works in exactly the same way. Once the radio buttons are grouped together, only one of the group may be active at a time. If the user clicks on one radio button, and then on another, the first radio button will first emit a toggled signal (to report becoming inactive), and then the second will emit its toggled signal (to report becoming active).

The following example creates a radio button group with three buttons and looks like this: