Tag Archives: mit app inventor

What is inside a .aia project file?

As you may know, you can save your App Inventor project to your local computer using the Projects | Export selected project (.aia) to my computer menu option:

ExportSelected

Use this feature to save a backup copy on your local computer or to share your code with others (email or transfer the file using DropBox – or similar – or merely copy to a USB thumb drive).

What is inside the .aia file?

Surprisingly, the .aia file is just a regular .zip file. You can verify by saving a copy to your local disk drive, and then rename the file to have a .zip file extension instead of .aia. Then use Windows Explorer, StuffIt Expander or other utility to open and decompress the .zip file.

PLEASE NOTE – DO NOT MODIFY THE CONTENT OF THESE FILES.  THIS INFORMATION IS NOT SOMETHING YOU NEED TO KNOW TO WRITE APP INVENTOR APPS AND IS PROVIDED “AS IS” “FOR YOUR INFORMATION” ONLY.

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Displaying web pages in your Android apps

Last year, I presented a short tutorial on displaying web pages from inside your App Inventor apps. Now, here is a some what improved version that prompts for a web address URL, checks to see if http:// has been entered, and if not, prepends http:// to the front of the address. Then the web page is displayed.

The Designer View

There is not much to the user interface – a text box to enter the web URL and a button to display the web page. The page then appears below the button, and the content may be scrolled on the screen.

To create this user interface, drag a horizontal layout onto the screen and then add a label for the “Web page URL” prompt, followed by a text box for the data entry. Then add the Display web page button.

From the User Interface section of the Palette, at the left of the Designer screen, drag and drop a WebViewer component on to the design area.

Screenshot_2015-02-10-15-15-17

 

The WebViewer is not a full Internet browser – it is a component that displays the specified web page only. The WebViewer does not support standard browser features, such as saving web page content nor does it provide a history of the web pages visited.

The Blocks Code

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Part 2: Sending numeric data using App Inventor Bluetooth communications

Part 1 of this tutorial introduced Bluetooth communications and implemented a simple method of sending text data back and forth between two Android devices over the Bluetooth wireless link. If you are not familiar with using App Inventor’s Bluetooth component, start with Part 1.

In Part 2, a data packet concept is introduced to guide the communications between devices, and is used to send a combination of text and numeric data. This section introduces the concept of binary numbers so that you can understand why we would handle text and numbers in different ways.

This tutorial modifies the user interface of both the client and server programs introduced in Part 1. Then, blocks code is added to send text and numeric data. Numeric data is sent as binary data using special methods of the Bluetooth components.

Related:

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Positive comments about MIT App Inventor from i-Programmer

App Inventor is an amazing way to create Android applications. You don’t need to be able to program to use it, but if you can then all the better.

All I can say is that as a programmer this is the first time in quite a while that a development environment and its associated “language” has brought a smile to my face. It’s not perfect, but if you give it a little room to grown on you might just smile as well.

Although App Inventor is sometime described as an educational toy that you can use to get kids interested in programming, don’t let this fool you into thinking that you can’t do real things with it. It makes a very good prototyping facility and a couple of the prototypes that I have created have actually ended up as final apps that are still in use.

via Getting started with MIT App Inventor 2.

I have the same thoughts about App Inventor too. App Inventor is much bigger than a tool for teaching programming.

Blocks Editing Tip: Arranging and collapsing blocks in the editor

As you develop your App Inventor program using the Blocks editor, do you find your blocks overlapping and crashing in to one another on the screen? You know, like this:

AIBlockMess

You can drag the blocks on the screen so they no longer overlap, but dragging each block is tedious (time consuming). But there is an easy way to automatically re-arrange the blocks.

  • Move the mouse pointer to any part of the white space outside the blocks
  • On Windows, right-click the mouse button
  • On Mac OS X, press Ctrl and click the mouse button

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Part 1: Basic Bluetooth communications using App Inventor

(Some very minor updates were made to this in November 2019).

This tutorial covers basic App Inventor Bluetooth communications  code.   Subsequent tutorials will add additional features. To implement and test this sample code, you need access to two Android devices – one to act as a Bluetooth “server” and the other to act as a “Bluetooth” client.

I tested this code using an old LG smart phone running Android 2.2 and a new Nexus 5 running Android 5.0.1.  I also tested this code using the Nexus 5 paired with a Nexus 7 tablet. (Update I have since also run this on an Honor 8 phone and a Pixel 2, with much newer versions of Android.)

This tutorial is lengthy – it introduces Bluetooth communications, then presents the user interface and blocks code for both the server and client programs, and then discusses how to set up the Bluetooth Communications link using “pairing”.

Downloadable App Inventor source code for the client and server is at the end of this post.

This is the first of several  posts on Bluetooth. This first post covers basic connections and the sending and receiving of text between two Bluetooth devices. The two halves of the link – client and server – are kept in separate apps to keep this simple,  however, it is possible for a single app to act as both a client and a server. A subsequent post will show how to send other types of data, such as numbers, and introduce additional features for using Bluetooth communications.

Related:

Introduction to Bluetooth

Bluetooth is the communications technology with a funny name.[1] Bluetooth is actually named for a long ago Danish king who worked to unite groups of people, which is similar to Bluetooth’s goal of interconnecting different devices.  The King’s real name was “Harald” but he had a nickname that translates as “Bluetooth” – no one knows for sure why he had this nickname but one thought is he had one dark tooth that may have appeared black or blue. And that is certainly an obscure way to choose a name for new technologies!

Bluetooth establishes a very low power, short range (up to 10 meters) communications link between two devices. Bluetooth uses the same frequency band (2.4 Ghz) as Wi-Fi, but uses different technology. Both Bluetooth and Wi-Fi use forms of spread spectrum radio links that result in signals moving around within a wide band in ways that enable sharing of the spectrum by multiple devices. But the two technologies serve different purposes, are  not identical, and cannot communicate with one another.

Bluetooth applications include common wireless headsets for wired and cellular phones, and in-ear cordless adapters for phones. Bluetooth is also used by cordless headphones and to exchange address cards between devices, and for industrial applications where sensors collect and send data into a network.

There are two forms of Bluetooth – classic Bluetooth, which  we use in the sample applications, and a newer version known as Bluetooth low energy, Bluetooth BLE, Bluetooth LE or Bluetooth Smart – all referring to the same new technology.  The newest Android devices running Android 4.3 or newer, usually support the newest Bluetooth Smart technology. Regardless, we use classic Bluetooth which is backwards compatible to older phones, and is the technology supported by App Inventor.

Setting up a Bluetooth devices involves “pairing” the two devices and establishing a connection. This will be covered later in this tutorial.

Footnote:

[1] Actually there is another communications technology with a funny name called TWAIN, which is an acronym for “Technology without and interesting name” (really!)

The Designer View

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Using TinyDB in App Inventor

(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.

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