The styles manager in BX allows us to apply pre-set values easily to the resources of any number of widgets. Suppose, for example, we wanted a pushbutton with a label indicating “Dismiss”, a bold font, with a black foreground and a somewhat olive-colored background; we could use the style editor as shown in Figure 6. Saving this style to a DismissButtonStyle, our style hierarchy tree would look like Figure 7. When we create a pushbutton and apply the style, it would look like Figure 8.
In addition to being able to apply styles to multiple widgets at once, styles can easily be made shareable so they are available to other applications being developed.
BX has two modes of looking at widget hierarchies: class and instance. Class mode indicates what the predefined appearance and behavior of a component will be, in effect defining new types. Instance mode tailors them for a particular widget or component, so we can tweak what makes them different from others of the same type.
From the most general class, we can define more specific sub-classes, each time progressively getting more refined or changing and overriding things as we go along.
To save time redesigning our standard layout, we can join a number of logically related widgets together into a single entity by turning it into a class. This makes reuse a snap, since all newly created classes get added to the palette.
To create a class containing one or more widgets, select the highest-level widget to use, then select the “Make Class” menu option. In the previous widget tree containing a form widget with a few buttons and a scrolled list, I performed the “Make Class” operation, and now have a new component called ListProcessor which I can treat as a stand-alone component. It is much more than a simple widget, because we avoid having to delve into the depths of Xlib, Xt and Motif, remaining at a relatively high level without ever giving up control of any of the underlying widgets.
In class mode, we can use the widget class tree to select which resources to expose, giving us a simplified means to control our newly created component without the clutter of having to view every resource of every widget it contains. As a convenience, any resources flagged as “exposed” have set type methods defined, so we don't have to worry about the exact Motif name for widget resources and the functions to set them.
New class methods (functions and procedures) and data can be added easily when we select the class entity in the browser. Our resource editor puts us into class edit mode automatically when we click the “New” button to add data or methods. (See Figures 9 and 10.)
Our resource editor now appears as shown in Figure 11, with the new entry inserted. We can now select the “Edit” button, and if needed, our source code will be generated before whatever source editor is brought up. At this point, we can look at our code with the cursor placed automatically on the line where our function starts.
One thing we notice from the snapshot in Figure 12 are the “user code block” begin and end comments around the user code blocks. Anything between these can be modified by the programmer. BX reserves the right to make changes outside of these user code blocks, but will otherwise not interfere. BX avoids clobbering user-written code by scanning for and skipping over sections that are reserved by the developer. At the beginning of a project, these are empty lines bounded by the comment delimiters. Throughout the BX-generated code, these comment blocks will be found before, during and after any major code operation. This may seem superfluous to the new GUI programmer used to having only callback code stubs generated, but they can be a big help in tweaking final production code for major systems.
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Enter to Win an Adafruit Pi Cobbler Breakout Kit for Raspberry Pi
It's Raspberry Pi month at Linux Journal. Each week in May, Adafruit will be giving away a Pi-related prize to a lucky, randomly drawn LJ reader. Winners will be announced weekly.
Fill out the fields below to enter to win this week's prize-- a Pi Cobbler Breakout Kit for Raspberry Pi.
Congratulations to our winners so far:
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Realizing the promise of Apache® Hadoop® requires the effective deployment of compute, memory, storage and networking to achieve optimal results. With its flexibility and multitude of options, it is easy to over or under provision the server infrastructure, resulting in poor performance and high TCO. Join us for an in depth, technical discussion with industry experts from leading Hadoop and server companies who will provide insights into the key considerations for designing and deploying an optimal Hadoop cluster.
Some of key questions to be discussed are:
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