Components, Tips

Using TinyDB in App Inventor

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(This post was completely rewritten and updated on October 30, 2015)

What is TinyDB?

TinyDB is a simple “database” that stores data on your phone or tablet. Unlike program variables that go away when your app is finished running or your phone is re-set, values stored in TinyDB remain on your phone for use the next time your app is run.

About Memory on your Phone or Tablet

Your smart phone or tablet typically has two primary types of memory: RAM and FLASH memory.

RAM stands for “random access memory” – but today we mostly think of RAM as memory that can be accessed very fast (as compared to Flash or hard drive memory storage). RAM retains values as long as power is applied to the RAM circuity. Once we turn off the power, the values stored in RAM are lost. (In some applications, extra batteries are used to continuously provide power to RAM even when the “normal” power is turned off.)

Flash memory retains values when the power is turned off. But access to Flash RAM is not as fast as access to conventional RAM memory.

Why is it called “Flash”?  There was an early version of memory technology where the memory was erased by literally flashing it with ultraviolet light. However the inventor of Flash RAM chose the name “Flash” for different reasons. Modern Flash RAM is read, written and erased electronically.

App Inventor variables are stored in RAM memory – and the content of RAM is erased or reset whenever the power is turned off. TinyDB, on the other hand, stores values in FLASH RAM, where the values remain even when the power is turned off.

Using TinyDB

TinyDB provides a simple way to store and retrieve data efficiently and to store the data in long-term storage.  TinyDB is based on the concept of a “tag” to identify the stored data, and the data value. Think of a “tag” as like using your name as your identification to look up your address:

Tag value: Martin

Value: 123 Main St, Anytown, USA

or

Tag value: Alexa

Value: 321 Other St, Someplace, USA

TinyDB uses the “tag” (such as Alexa) to quickly locate the corresponding value. Even if you have 100 names and addresses stored in TinyDB, TinyDB can  look up the “tag” quickly and use the tag to find the corresponding value. We do not need to know how TinyDB does its look up so fast – it just does it [see Footnote 1].

In most database programs, the “tag” is known as a “key” or “key value”. App Inventor uses the name “tag” in place of “key”. As I am used to the name “key”, I tend to use “key” were I should have used “tag” in App Inventor! You will see this is the sample program, below!

To learn how to put TinyDB in operation, we construct a very simple app, described below.

Continue reading Using TinyDB in App Inventor →

Tips

AI Companion and your phone’s battery

On my phone, if I leave AI Companion running, the battery life of my phone goes down more rapidly.

Consequently, when I am done working on an app on my phone, I go in to Settings | Apps on the Android phone, find MIT App Inventor in the applications list, select it, and then select Force Stop.

I have no idea if other people experience this problem but the fix is simple – just kill the AI Companion app if its no longer needed.

This issues appears to be because the AI Companion links to the App Inventor cloud-based editor – as you edit and make changes, those changes are copied from the editor back to your device, almost in real time. However, if you walk away from the computer and the phone, neither realizes you left for a cup of coffee or to walk the dog – and they may continue to chat with each other, draining the battery.

Regardless, when developing apps for your phone or tablet, your best bet is to turn off battery saving features and leave your phone on (so you don’t have to continually enter your pass code or otherwise restart the phone after it goes to sleep). AND – very important – leave it plugged into a charger. Taking these steps can make your app development go more smoothly.

Tips

You can run App Inventor and install apps to your phone at Starbucks

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As you already know, you can use App Inventor and the AI Companion on your phone to install apps from your computer (Browser) to your smart phone, as long as both are on the same network.

This works at Starbucks too 🙂 Just run appinventor.mit.edu to access your app in the cloud, run the MIT AI Companion app on your phone, and then select Connect | AI Companion in the browser window.

The app installs on to your phone.

Components

App Inventor’s File access component

In the Designer, under Storage, drag the File component to the user interface Design screen.  This adds a “non-visible component” at the bottom of the Designer canvas area.

In the Blocks view, scan down the list of blocks until you find File1 (you can  rename it to something else). You’ll find a set of functions for writing to files and reading from files.

This component can write text to files and read text from files. If you are familiar with other programming systems and concepts, this type of file and its use are called “sequential files”.  Since Comma Separated Values (CSV) files are a formatted version of text files, you can also convert lists into CSV rows and write those to the file, creating text files filled with data that can be read into spreadsheet programs.

Documentation

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!

Learn to program with App Inventor