Using App Inventor’s Official Documentation pages

Using App Inventor’s Official Documentation

App Inventor programming uses graphical components to layout program functionality. But the official App Inventor documentation uses a traditional programming textual description. When you reference the documentation you see a (mostly) textual description of “Properties”, “Methods” and “Events”.

In the App Inventor Designer, you should see a question mark inside a circle  next to each component (just to the right) in the Palette. Clicking on the question mark brings up a pop up dialog box with a brief description of the component. At the bottom is usually a “More information” hyper link. When you click on that link, documentation pages open in a new browser tab. And this is where you will see information described in “Properties”, “Methods” and “Events” sections.

Events

Inside App Inventor (and within Android) lie the concept of an “event driven” programming model and object oriented programming. The former is easy to understand: a “When xxx.Click Do” block describes what to do when an “event” occurs such as a user presses a button on the screen. That button push is an event.  Our program blocks respond to events – and specify what our program does when the event occurs.

Properties

You have seen properties on the Designer page – at the right hand side, you can change the color of buttons or change the text of a label. Each of these values is a “property” of the component.

The concept of a property is easy to understand by seeing how properties apply to every day objects.  A car might have the property “blue in color”.  A house might have a property “yellow in color”.  A dog might have a property like “breed is german shepherd” or “small dog” or “large dog”.

Real world objects can have multiple properties. For example, a car could be “blue in color”, “4 wheel drive”, “4 door” and “140 horsepower engine”. Each of these attributes is a property that helps to describe the car.

In App Inventor, each component may have a set of properties. For example, a button might be square or oval, or blue or gray in color. Each of these attributes is a property – for example, the color property might be set to “blue”.

Methods

“Methods” describe the actions or services the component can provide for a program. A method labeled “Start()” is an action that the component can perform.

Another way to describe “properties” and “methods” is to describe them in terms of human language – a property is like a noun “small”, “large”, “blue” (as in color) and a method is like a verb describing an action.

In this way, each component is an “object” that has properties and can provide services and perform an action (the methods).

In terms of real world objects, a car might have methods such as “start engine”, “stop engine”, “increase throttle”, “decrease throttle” and “set throttle” (to a specify speed).

Back to the Documentation

When you look at the App Inventor documentation online, you will see a list of properties, events and methods.

For example, the media player plays audio or sound. It has a property “Volume” set between 0 and 100 to adjust the player volume. And it has methods such as “Start()” to begin playing the sound and “Stop()” to end playing the sound.

Now that you know what “properties”, “events” and “methods” actually mean, you should find reading the documentation to be a bit easier!

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s