Question

I’m in the process of diving into Android development. Most of the projects I was involved with, were in C#. Delegates were elements of C# I did use very often, I’ve used also stuff like passing data using class that extends EventArgs or properties with set and get. With my programming knowledge I think I will be able to get started with Android development pretty smoothly. The thing is I have completly no idea how to approach an implementing mechanism similar to C# delagte in Java.

Below I present some exemplary class that works in C# just fine and contains some elements of C# language that I would like to use in my future Android projects. Can someone provide me with a translation of this code? I would prefer that ‘cos working with my own example and its conversion would allow me to catch it all faster. Also, any valuable resources on the topic (not only delegates but genereal topic of converting C# into Java) would be apreciated.

CountdownTimer.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace SampleDelegateApp
{
    public class CountdownTimer
    {
        Timer tmrTicks = new Timer();
        int secondsLeft = 0;
        int numberOfSecondsToCountdown = 0;

        public bool IsWorking
        {
            get { return tmrTicks.Enabled; }
        }

        public CountdownTimer(int seconds)
        {
            if (secondsLeft < 0) secondsLeft = 0; 
            numberOfSecondsToCountdown = seconds;
            secondsLeft = seconds;

            tmrTicks.Interval = 1000;
            tmrTicks.Tick += new EventHandler(tmrTicks_Tick);
            tmrTicks.Enabled = false;
        }

        void tmrTicks_Tick(object sender, EventArgs e)
        {
            secondsLeft--;
            if (secondsLeft >= 1) 
                WhenCountdownTimerTick(new CountdownTimerEventArgs(secondsLeft, numberOfSecondsToCountdown, false));
            else
            {
                Stop();
                WhenCountdownTimerTick(new CountdownTimerEventArgs(secondsLeft, numberOfSecondsToCountdown, true));
            }
        }

        public void Reset()
        {
            Stop();
            secondsLeft = numberOfSecondsToCountdown;
            if (secondsLeft < 0) secondsLeft = 0;
            WhenCountdownTimerTick(new CountdownTimerEventArgs(secondsLeft, numberOfSecondsToCountdown, false));
        }

        public void Stop()
        {
            tmrTicks.Enabled = false;
        }

        public void Start()
        {
            if (secondsLeft <= 0)
            {
                secondsLeft = 0;
                WhenCountdownTimerTick(new CountdownTimerEventArgs(secondsLeft, numberOfSecondsToCountdown, true));
            }
            else
            {
                tmrTicks.Enabled = true;
            }
        }

        public delegate void CountdownTimerTickEventHandler(object sender, CountdownTimerEventArgs ea);

        public event CountdownTimerTickEventHandler CountdownTimerTick;

        protected virtual void WhenCountdownTimerTick(CountdownTimerEventArgs ea)
        {
            if (CountdownTimerTick != null)
            {
                CountdownTimerTick(this, ea);
            }
        }
    }

    public class CountdownTimerEventArgs : EventArgs
    {

        public string timeString = "";
        public float procentOfTimeLeft = 0.0f;
        public bool countdownFinished = false;

        public CountdownTimerEventArgs(int secondsLeft, int SecondsToCountdown, bool isfinished)
        {
            countdownFinished = isfinished;
            timeString = string.Format("{0:00}:{1:00}", secondsLeft / 60, secondsLeft % 60);
        }
    }
}

frmTest.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace SampleDelegateApp
{
    public partial class frmTest : Form
    {
        CountdownTimer ctmrTest;

        public frmTest()
        {
            InitializeComponent();
            ctmrTest = new CountdownTimer(-44);
            ctmrTest.CountdownTimerTick += new CountdownTimer.CountdownTimerTickEventHandler(ctmrTest_CountdownTimerTick); 
        }

        void ctmrTest_CountdownTimerTick(object sender, CountdownTimerEventArgs ea)
        {
            lblTimer.Text = ea.timeString;
            if (ea.countdownFinished) countdownEnd();
        }

        private void btnStart_Click(object sender, EventArgs e)
        {
            ctmrTest.Reset();
            ctmrTest.Start();
        }

        void countdownEnd()
        {
            MessageBox.Show("Finish");
        }
    }
}

Answer 1

I apparently used some words in my question that made it all unclear and/or persons who tried to help me completly missunderstood my needs as for this question. Putting word “delegate” here and there made it even more complexed. After one more question asked in other way i got my answer that made me able to answer my question:

How to achieve c# event behavior in java (Android)

I’m not saying that code below is up to the best coding standards, and example shown here got any use in real life project, but this is exactly what i was looking for. Below working example:

tester.java

public class tester{
    public static void main(String[] args) {
        test test1 = new test(); 
        test1.start();
    }
}

test.java

public class test implements CountdownTextTickListener {

    public test() { }

    public void start() {
        CountdownText ctx = new CountdownText(100);
        ctx.setListener(this);
        ctx.Start();
    }

    @Override
    public void CountdownTextTickEventFired(Object sender, 
                        CountdownTextTickEventArgs eventArgs) {
            System.out.println(eventArgs.TimeString);
            if(eventArgs.isStopped) System.out.println("- END -");
    }
}

CountdownTextTickListener.java

public interface CountdownTextTickListener {
     void CountdownTextTickEventFired(Object sender, CountdownTextTickEventArgs eventArgs);
}

CountdownTextTickEventArgs.java

public class CountdownTextTickEventArgs {

    public String TimeString = "";
    public boolean isStopped = false;

    public CountdownTextTickEventArgs(int seconds, boolean isStoppedState) {
        TimeString = String.format("%02d:%02d",seconds/60, seconds % 60);
        isStopped = isStoppedState;
    }

}

CountdownText.java

import java.util.Timer;
import java.util.TimerTask;

public class CountdownText {

    Timer tmrTicks = new Timer();
    int secondsLeft = 0;
    int numberOfSecondsToCountdown = 0;
    boolean isWorking = false;
    private CountdownTextTickListener listener = null;

    public boolean getIsWorking(){
        return isWorking;
    }

    public CountdownText(int seconds) {
        if (secondsLeft < 0) secondsLeft = 0; 
        numberOfSecondsToCountdown = seconds;
        secondsLeft = seconds;
    }

    void startTimer() {
        isWorking = true;
        fireEvent(secondsLeft, false);
        tmrTicks = new Timer();
        tmrTicks.scheduleAtFixedRate( new TimerTask(){
            @Override
            public void run(){
                tickTimer();
            }
        }, 1000, 1000); 
    }

    private void stopTimer() {
        isWorking = false;
        tmrTicks.cancel();
    }

    private void tickTimer() {
         secondsLeft--;
         if (secondsLeft >= 1) 
         {
             fireEvent(secondsLeft, false);
         }
         else
         {
             Stop();
             fireEvent(secondsLeft, true);
         }
    }

    public void Reset() {
        Stop();
        secondsLeft = numberOfSecondsToCountdown;
        fireEvent(secondsLeft, false);
    }

    public void Stop() {
        stopTimer();
    }

    public void Start() {
        if (secondsLeft <= 0)
        {
            secondsLeft = 0;
            fireEvent(secondsLeft, true);
        }
        else
        {
            startTimer();
        }
    }

    protected void fireEvent(int seconds, boolean isStoppedState) {
        if (listener != null) {
            Object sender = this; 
            CountdownTextTickEventArgs eventArgs = new CountdownTextTickEventArgs(seconds, isStoppedState);
            listener.CountdownTextTickEventFired(sender, eventArgs);
        }
    }

    public void setListener(CountdownTextTickListener listener) {
        this.listener = listener;
    }
}