com.pi4j.jni.AnalogInputMonitor Maven / Gradle / Ivy

package com.pi4j.jni;

/*
 * #%L
 * **********************************************************************
ORGANIZATION  :  Pi4J
PROJECT       :  Pi4J :: Java Library (Core)
FILENAME      :  AnalogInputMonitor.java

This file is part of the Pi4J project. More information about
this project can be found here:  http://www.pi4j.com/
**********************************************************************
 * %%
 * Copyright (C) 2012 - 2018 Pi4J
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 *
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */


import com.pi4j.util.NativeLibraryLoader;

import java.util.Vector;

/**
 * 
 * This class provides static methods to configure the native Pi4J library to listen to GPIO
 * analog input value changes and invoke callbacks into this class. Additionally, this class
 * provides a listener registration allowing Java consumers to subscribe to GPIO analog input
 * value changes.
 * 
 *
 * @see http://www.pi4j.com/
 * @author Robert Savage (http://www.savagehomeautomation.com)
 */
public class AnalogInputMonitor {

    private static Vector listeners = new Vector<>();
    private Object lock;

    // private constructor
    private AnalogInputMonitor()  {
        // forbid object construction
    }

    static {
        // Load the platform library
        NativeLibraryLoader.load("libpi4j.so");
    }

    /**
     * 
     * This method is used to instruct the native code to setup a monitoring thread to monitor
     * analog input values for changes on the selected GPIO pin.
     * 
     *
     * @param pin GPIO pin number
     * @param pollingRate the polling rate in milliseconds for the input monitoring thread to
     *                    read analog input values from the hardware
     * @param changeThreshold the amount of change (delta) in the analog input value required before a new
     *                        analog input change event is dispatched.
     * @return A return value of a negative number represents an error. A return value of '0'
     *         represents success and that the GPIO pin is already being monitored. A return value
     *         of '1' represents success and that a new monitoring thread was created to handle the
     *         requested GPIO pin number.
     */
    public static native int enablePinValueChangeCallback(int pin, int pollingRate, double changeThreshold);

    /**
     * 
     * This method is used to instruct the native code to stop the monitoring thread monitoring
     * analog input values on the selected GPIO pin.
     * 
     *
     * @param pin GPIO pin number

     * @return A return value of a negative number represents an error. A return value of '0'
     *         represents success and that no existing monitor was previously running. A return
     *         value of '1' represents success and that an existing monitoring thread was stopped
     *         for the requested GPIO pin number.
     */
    public static native int disablePinValueChangeCallback(int pin);

    /**
     * 
     * This method is provided as the callback handler for the Pi4J native library to invoke when a
     * GPIO analog input calue change is detected. This method should not be called from any Java
     * consumers. (Thus it is marked as a private method.)
     * 
     *
     * @param pin GPIO pin number
     * @param value New GPIO analog input value
     */
    @SuppressWarnings("unchecked")
    private static void pinValueChangeCallback(int pin, double value) {

        Vector listenersClone;
        listenersClone = (Vector) listeners.clone();

        for (int i = 0; i < listenersClone.size(); i++) {
            AnalogInputListener listener = listenersClone.elementAt(i);
            if(listener != null) {
                AnalogInputEvent event = new AnalogInputEvent(listener, pin, value);
                listener.pinValueChange(event);
            }
        }
    }

    /**
     * 
     * Java consumer code can all this method to register itself as a listener for pin analog
     * input value changes.
     * 
     *
     * @see AnalogInputListener
     * @see AnalogInputEvent
     *
     * @param listener A class instance that implements the AnalogInputListener interface.
     */
    public static synchronized void addListener(AnalogInputListener listener) {
        if (!listeners.contains(listener)) {
            listeners.addElement(listener);
        }
    }

    /**
     * 
     * Java consumer code can all this method to unregister itself as a listener for pin analog
     * input value changes.
     * 
     *
     * @see AnalogInputListener
     * @see AnalogInputEvent
     *
     * @param listener A class instance that implements the AnalogInputListener interface.
     */
    public static synchronized void removeListener(AnalogInputListener listener) {
        if (listeners.contains(listener)) {
            listeners.removeElement(listener);
        }
    }


    /**
     * 
     * Returns true if the listener is already registered for event callbacks.
     * 
     *
     * @see AnalogInputListener
     * @see AnalogInputEvent
     *
     * @param listener A class instance that implements the AnalogInputListener interface.
     */
    public static synchronized boolean hasListener(AnalogInputListener listener) {
        return listeners.contains(listener);
    }
}