Language - Android Java

Preamble about the language and its general strengths and weaknesses.

Assessment for use with Phidgets

On the Android platform, Java is currently the only available language.

Support

Phidgets can run directly plugged in to Android devices with a USB port and system 3.1 or later.

Otherwise, Android can control a Phidget remotely over a network, by using the Phidget Webservice.

Development Environments and Compilers

The Phidget examples given below -- as well as the Android SDK examples given by Google -- use Eclipse for a development environment.

To download and configure Eclipse to work with the Android SDK and the Phidget Libraries, please see the OS - Android page.

Drivers, Libraries and Resources

• Phidget Libraries for Android
• The Phidget Webservice should be installed on the remote computer hosting a Phidget for an Android device to control
• Phidget Examples for Android
• The Java API for using Phidgets
• You might also find the General Java page helpful, as it has more Java examples.

When you download and unzip the Phidget Library for Android, it will contain three things:

1. A libs/ folder
2. A jar file containing the general Phidget java library (phidget21.jar)
3. A jar file for directly driving USB devices from a USB port on the Android device (PhidgetsUSB.jar)

How to use this library is described below.

Remote Phidget Use

To install libraries to run a Phidget remotely:

• Add libs/ and phidget21.jar to your project
• Add the following to your AndroidManifest.xml file:

    <uses-permission android:name="android.permission.INTERNET"></uses-permission>

Direct Phidget Use

To install libraries to run a Phidget directly (Android 3.1 and later, with USB port on device):

• Add libs/, phidget21.jar, and PhidgetsUSB.jar to your project
• Add the following to your AndroidManifest.xml file:

    <uses-feature android:name="android.hardware.usb.host" />

In Eclipse

In Eclipse, jar files and library files can be added to a project by:

• Project → Properties → Java Build Path → Libraries (tab) → Add JAR
• Project → Properties → Java Build Path → Libraries (tab) → Add Library

Getting Started

Import an Existing Example

Unpack the Phidget Examples for Android.

Import one of the Existing Eclipse Projects:

• File → Import... → General → Existing Projects Into Workspace → (Next)
• Select root directory → Browse to find and select an existing example such as the InterfaceKitExample

Select all files, click Finish

Right-click on project in Package Explorer (To open this, use Window → Show View → Package Explorer)

Select Run As... → Android Application

This will bring up the Android Virtual Device manager window. If your Android hardware is plugged in to your debugging computer, you will see the hardware as an option on which to run the example. Otherwise, make sure you have an Android Virtual Device (AVD) set up to run the example on (you can do this by clicking New... on the right side).

Coding For Your Phidget

Before you can use the Phidget, you must include a reference in the code to the library. In Android Java:

  // This contains all of the devices and the exceptions
  import com.phidgets.*;

  // This contains all of the event listeners
  import com.phidgets.event.*;

Remember to add your libraries and .jar files to where Java can find them. For Eclipse, this is described above in the Libraries and Drivers section.

Connecting to the Phidget

Before writing code of your own, it may help to read about Event Driven Code before proceeding.

In your code, you can open and connect to a Phidget using open() or openAny().

Next, the program needs to try and connect to the Phidget through an open call. The open will tell the program to continuously try to connect to a Phidget, based on the parameters given, even trying to reconnect if it gets disconnected. This means that simply calling open does not guarantee you can use the Phidget immediately. We can handle this by using event driven programming and tracking the AttachEvents and DetachEvents, or by calling waitForAttachment. WaitForAttachment will block indefinitely until a connection is made to the Phidget, or an optional timeout is exceeded.

  ik.openAny();
  ik.waitForAttachment();

The parameters can be used to open the first Phidget of a type it can find, open based on its serial number, or even open across the network. The API manual lists all of the available modes that open provides. One important thing to remember is that when working with Phidgets, a local connection will reserve the device until closed. This prevents any other instances from retrieving data from the Phidget, including other programs. The one connection per device limit does not apply when exclusively using the Phidget Webservice. At the end of your program, don’t forget to call close to free any locks on the Phidget.

  ik.close();
  ik = null;

Event Driven Programming

We recommend the use of event driven programming when working with Phidgets. In Java, we hook an event handler with the following code:

  ik.addSensorChangeListener(new SensorChangeListener()
  {
      public void sensorChanged(SensorChangeEvent se)
      {
        //Insert your code here
        System.out.println(se.getValue());
      }
  });

With this method, the code inside sensorChanged will get executed every time the PhidgetInterfaceKit reports a change on one of its analog inputs. The items from the event, such as the index or reported value, can be accessed from the SensorChangeEvent object properties. Some events such as Attach and Detach belong to the base Phidget object and thus are common to all types of Phidgets. Please refer to the API manual for a full list of events and their usage.

Working Directly With the Phidget

Some values can be directly read and set on the Phidget. Simply use the instance’s properties or call member functions such as getSensorValue(int index) or setOutputState(int index, boolean newVal) for PhidgetInterfaceKits. These methods can be used inside a polling loop as an alternative to event driven programming.

Building your Project

Describe the different ways a project could be built using this language.

Common Problems and Solutions/Workarounds

This section contains some Android Java and Eclipse-specific common problems. For more answers about using Phidgets, visit our forums, FAQ, or contact us.

Error: Unable to get view server protocol version from device emulator
Likely Fix: Project → Clean... → Clean All (If that does not work, clean again and restart Eclipse)

Error: Android requires compiler compliance level 5.0 or 6.0. Found 'X.Y' instead
Likely Fix: The javac and java version on the example do not match those on your computer.

• Find the version of java and javac on your computer (for example, java -version on the command line)
• In Eclipse, open the Package Explorer (Window → Show View → Package Explorer)
• Find the project, right-click and select Properties
• In Properties → Java Compiler → (Checkbox) Enable Project Specific Settings → Set Compiler Compliance Level = Java Version → Apply
• When told this requires rebuild, say Rebuild Now