Some times App Inventor 2 apps stop working (well mine sometimes do this, may be your’s don’t!)

Besides looking carefully at your blocks code, there are some additional steps that may be helpful in identifying the cause of the problem.

1. Check your blocks code very carefully to see if you can spot an error in your program.

2. Add a status message area in the user interface (using the Designer) and then in your blocks code, add blocks to assign status texts to this message area. Your status message could include a message indicating what section of your code is running, or to display the values of variables in your program.

3. Add a special “Error handler” to catch and display information when the program encounters a serious problem. The following section is adapted from my tutorial on basic Bluetooth communications.

Error  Handling

For most of our App Inventor apps, we ignore potential errors – if errors occur, the app stops running and Android displays error messages.

Our app can intercept the error condition by adding an error event handler to the main screen, Screen1. In the Blocks editor, select the Screen1 component and then select the When Screen1.ErrorOccurred event. Drag this to the Blocks editor and then add the following code.

The ErrorOccurred event has four parameter values (local variables) that contain information about the error. This error handler displays the error values on your device screen, rather than immediately shutting down the app.

To use this code, add a text label to your user interface – in the example above, the label has been renamed to lblStatus.

There is no guarantee that these error values will identify the specific problem but they may give an indication as to where the problem is occurring in your program!

Android phones and tablets support Bluetooth communications (“BT”).

BT is a very low power, very short range communication technology used for connecting earphone and headphone adapters, wireless microphones, and wireless keyboards and mice to computers and tablets.

App Inventor supports BT links and can be used to transmit data back and forth between two Android devices.

When two devices communicate, one device acts as a “server” and the other as a “client”, although either send and receive data.

I now have basic Bluetooth communication working between two Android phones. As I finalize the Bluetooth sample app, I will post a tutorial here on how to set up Bluetooth and how to write apps that use Bluetooth communication.

Longer term, I intend to connect an App Inventor app to an Arduino microcontroller board using the Bluetooth link. I will post information on that once it is available.

(Due to volunteering every evening with a FIRST Robotics team, and a few extra things going on, my updates are a little less frequent at the moment – sorry!)

This post is a major update to a previous post on reading and writing text files using App Inventor. This revision includes information on how to locate the text files you create in your App Inventor apps, plus how to transfer those files from your smart phone or tablet to your computer.

An earlier blog post described how to store data using TinyDB so that an app’s data can persist between uses of the program, or even to share data between screens in a program.

Another way to save data is to write the data to a file on your Android device. App Inventor has introduced a File control that lets us write text data to a file and then read it back, later. As we will see, the File control is not the easiest thing to use but with some work, the control can be used to store data from our program into a file.

Once data is in a file, you could, hypothetically, transfer the file from an Android to device to another computer. Because Android stores the files in a way that they may not be readily accessible – or even visible – we need to use some simple tricks to find the file and transfer the file to a computer.

Update: To learn more about text files and transferring data in the CSV file format, check out Volume 3 of “App Inventor 2 Databases and Files” – thanks!

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