Line Create the form; however, it is still not visible! Line Create the command button; again, it is not visible. Line Connect the function on line 03 with the "clicked" event of the command button. Line Add the button to the window the container object. Line Make all widgets visible.
Until now, all widgets have been invisible. This action is known to substantially increase the usefulness of any GUI application. Line Exit status; required for every C program. As you can see, this is not terribly difficult "for C," some of you are saying. You could have just as easily made it HelloWorld. You can omit -o HelloWorld from the preceding command; if you do, it will create a file called a. The -Wall instructs the gcc compiler to display all warnings, and the -g option instructs the compiler to include debug information for use with a debugger.
If you want to avoid retyping, you could put the preceding line into a shell script the Linux equivalent of a batch file, but it's not as good as a makefile. For example, if the shell script is named build. You could also think of it as a macro because it stands for something else that will be expanded at the time the information is needed. This is important: The gtk-config program is surrounded by back ticks, not single quotation marks! The back ticks tell gcc to execute the enclosed program. That is, a window is a container: You add child widgets to it, and those child widgets fill the space they are given and automatically resize and adjust when their parent widget resizes or otherwise changes shape.
Notice that this happens in HelloWorld see Listing 2. The window widget has one child widget. If you resize the window, the button widget changes shape as well.
Both are grid widgets on which you can lay out other child widgets, but when the size of the window changes, the child widgets placed on the GtkFixed or GtkLayout widget will not change size or location. The primary difference between the GtkFixed widget and the GtkLayout widget is that the GtkLayout widget has scroll bars that allow you to move around within the window if the window size becomes smaller than the displayable child widgets. The GtkFixed widget will simply cut the child widgets out of view.
For the user to see them or even know they are there!
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A Note of Caution By using the GtkFixed or GtkLayout widget, you might have an easier start, but you will probably run into a problem getting your window widget to default to the right size to properly display all the child widgets correctly. Be sure to thoroughly study the functions for sizing windows. In Figure 2. This looks very familiar to VB developers; when this window size is changed, the child widgets placed on the grid will not change size. Figure 2. GtkWindow plus GtkLayout. Anyone who has developed VB applications for long learns to hate setting the tab order that is, the order the cursor follows from control to control when the user presses the Tab button.
For industrial-strength application dataentry tasks, this can become a very important issue because users will quickly want to move from the mouse to the keyboard to navigate the form.
This was one of the things the "old DOS screens" could do very well. Once the user got used to a certain set of keystrokes, he could enter massive amounts of data very quickly by keying ahead of the screen, and the buffer would hold the key strokes and process them in time. As I said at the start, though, this can be a blessing-but it can also be a curse.
You decide. It can be a blessing because you do not have to code for tab order; it can be a curse because you cannot control the order. When resized, they automatically resize their child widgets.
A parent widget is one that contains children widgets. The following sections describe the most common of these packing widgets. You can set policies, such as whether or not all children should remain the same size and how much spacing there should be between child widgets. See the sample program at the end of the chapter to get a feel for how to use and control these widgets. Additionally, you can pack the boxes from either the start top, or left or the end bottom, or right.
You can set the same options you could for the preceding widgets, and you can specify that certain widgets should occupy more than one space in the grid. GtkWindow This is the main window widget; note that it is not a window into which you can add controls, but it is only a container meaning that you can add one widget to it-for example, a command button as in HelloWorld.
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If you want to add more than one widget, you must add another container control to the window, such as a GtkTable widget, into which you can add multiple widgets. With the window widget, you have your basic window frame, with window handles around the edges of the window and the Close, Minimize, and Maximize buttons. That's it!
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The default size is x pixels. See Listing 2. A Note on Multiple Window Programs If your program uses several windows and you need to pass data back and forth between the windows, you have a couple of choices. First, of course, you can make the necessary widgets or all of them, for that matter global in scope.
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This, of course, allows you the most and quickest flexibility, but it will also get you into trouble eventually with a program of any size or complexity. The other choice is to keep your global objects in other words, the top-level windows to a minimum and query them for the values in the child widgets they contain.
This second option will be covered in more detail in Chapter 5. The first option is used in the "tour de widgets" program that follows because it is a rather simple program and its purpose is to demonstrate widget functionality, not give a lesson in variable scope. Although the global-variables option may seem easy and quick, the Glade paradigm of interrogating window widgets for child widgets is actually extremely simple and easy to implement, as you shall see.
Actually, this makes sense from a software engineering standpoint: What could be more "global" than your top-level windows?
That is, it does not have one large container window in which the multiple windows of the application "float," or "dock," but still contains the multiple windows in one top-level window and shows one item on the taskbar. Glade is a good example of this; see the figures in Chapter 5. The running program is designed to demonstrate the functionality of these widgets.
It does nothing special, but it attempts to tie together some of the more common widgets to show how they work. Normally, they would be the only global variables, but in order to demonstrate widget functionality, many widgets are declared global that normally wouldn't be in a production application. See the "lookup widget" function in support. The label has no events. There will be two different groups of radio buttons: one in which the group is created manually and one in which the group is created automatically. First, the hard manual way Remember,, the GtkFrame object does not automatically group radio buttons for you.
For each of the three following radio buttons, the first line creates the radio button, and the second line adds it to grp1. Remember, grp1 is of type GSList. This is required by the function. So, the macro takes care of this. The definition of the adjustment is as an object. So, declaring it here as an object prevents "cast-from-incorrect-type" errors when the program is compiled.
If you declared it as type GtkWidget, the program would compile and run, but the results might not be what you expect. As you can see if you resize the form, the GtkText widget will simply wrap lines at each letter, not each word. First, you need a small horizontal box to contain the widgets.
An adjustment object abstracts the behavior out of the spin button, allowing you to set the min, max, default, etc. Another note: You can use the same adjustment object for multiple spin buttons, but then they will behave as if they are tied to one another, which means that when you adjust one, the other will mirror that action. What about a window? Try it.