Why App Inventor Works

Sharon Michaels wrote a great review of App Inventor and like many lauds its visual, drag-and-drop interface.  In teaching App Inventor for a year, I’ve seen that it does work for non-programmers and I’ve thought a great deal about why. Here are the key features of the language:

No syntax — The blocks language eliminates the need to remember and type code. When I teach beginners textual languages, their biggest pain is syntax, the blank page, and the cryptic error messages that Python/Java/etc. provides for them. Most beginners quit because of the frustrating experience of syntax errors.

Events at the top level — Traditional programming languages  were designed when the best metaphor for a program was “a program is like a recipe– a set of instructions”.

Since the advent of the graphical user interface, programs have not been recipes, but sets of event-handlers. “When this happens, the app does this. ” is the correct conceptual model.

With App Inventor, an app is a set of event-handlers. I know this is amazing, but you can say, “when a user clicks this button, ” by dragging out a block. Compare this with Java, which requires you to understand classes, objects, and listeners in order to express an event-handler. Even if App Inventor were a textual language, its 1st order events would dramatically ease the development task.

Choose from a set of options — The components and functions are organized into drawers. You program by finding a block and dragging it into the program. You don’t have to remember how to enter an instruction or refer to a programming manual.

Only some blocks plug-in — Instead of chastising the programmer with cryptic error messages, App Inventor’s blocks language restricts the programmer from making mistakes in the first place. For instance, if a function block expects a certain type of parameter, you aren’t allowed to plug in a different type. This doesn’t eliminate all errors, but it sure helps.

Concreteness — You program components, not abstractions. When you drag out a component, an object is created and function blocks created for it. This is a problem in terms of code reuse and program size, but the concreteness is a boon for beginners and is pretty nice for experts as well.

High-level components — The app inventor team has built a great library with simplicity the main goal. There are months of programming expertise embedded in the components.


5 Responses

  1. Lame. If somebody is so thrown off by syntax errors, they should stick to something simple. Like automotive repair or something.

  2. Got an invite – played with it for a few minutes and managed to crash not only the blocks editor, but also the program on the phone. Still a few holes left to fill i think 😉

  3. […] Why App Inventor Works […]

  4. Otto, Take your cars transmission apart and reassemble it using only a chinese handbook for instruction. Hard ? perhaps there are different minds for different jobs. some will follow the pictures, some will rely on words, others need to do it manually, step by step and feel how the transmission works. Either way, the first time a transmission is spread over your garage floor you won’t find it easy to put together. and yes this is an anology

  5. Why doesn’t Google App Inventor give you the source code?…

    If you mean to ask why App Inventor doesn’t provide user accessible source code of apps, this is an intentional design decision related to the main intended educational use of App Inventor, i.e. teaching programming to non programmers. The syntax of t…

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