Instruction

by Paweł Paduch published 2021/10/28 16:38:05 GMT+2, last modified 2021-10-28T16:38:05+02:00

Delegates, Events and Timers

Simple Delegate (1,0)

delegate void PrintSomething(string sth);

static void PrintOryginal(string sth)
        {
            Console.WriteLine(sth);
        }

 static void PrintInCapital(string sth)
        {
            Console.WriteLine(sth.ToUpper());
        }

 static void Main(string[] args)
        {
            PrintSomething printingDelegate = new PrintSomething(PrintOryginal);
            printingDelegate("Hello World");
            printingDelegate = new PrintSomething(PrintInCapital);
            printingDelegate("Hello World");
            printingDelegate += new PrintSomething(PrintOryginal);
            printingDelegate("Hello New World!");
            Console.WriteLine("Printing delegate has following methods:");
            foreach (var item in printingDelegate.GetInvocationList())
            {
                Console.WriteLine(item.Method.Name);
            }
        }

Base on the code of the SimpleDelegate project, define a delegate of type void with two parameters of type int.
To the given delegate create 4 methods that print sum, difference, quotient and product.(+,-,/,*)
Add the new methods from the previous section to the delegate invocation list.
Call delegate
Print the method names from the delegate invocation list.

Ending v1 (0,5)
- Run Project SimpleEvent.
- Even when you press any key, the program does not end.
  The reason is waiting for the child process.
- In the method startClock set the thread property IsBackground to the true.
- Restart. Press any key without waiting for the event to start.
Ending v2 (1,0)
- Comment on the line just added
- Let the Alarm class implement the IDisposable interface
- This is mainly about the Dispose, method in which we will perform the Interrupt() operation on the internalTrhead thread and then assign it null
- The thread should handle the ThreadInterruptedException exception, causing it to terminate with an appropriate message.
- In Main immediately after reading the key, call alarm.Dispose();
- Launch the program. Check the functionality.
Possibility to set checkingInterval (0,5)
- Overload the constructors and methods of SetAlarm for the option to specify checkingInterval.
- Currently, the default is 1000ms.
Add new Event (1,0)
- Add a timespanToAlarm remaining time counter update, and a read-only property that returns this value.
- Add an event triggered on every check
- Along with checking, the event should return the remaining time to an alarm.
- Add handling of a new event. Demonstrate the operation in the program.
TimerExampe (0,5)
- Run the project TimerExample.
  We see that timerThreading is started after five seconds with one-second intervals.
  On the other hand, timerSystem starts immediately and at intervals of 1.5s
- Add the line
  timerSystem.AutoReset = false;
  This will make the timer act as a one-shot alarm clock.
- We add a counter. Add the following method to the program:
```
private static void TimerTask(object timerState)
    {
        Console.WriteLine($"{DateTime.Now:HH:mm:ss.fff}: starting a new callback.");
        var state = timerState as TimerState;
        T.Interlocked.Increment(ref state.Counter);
    }
```
- Add class
```
    class TimerState
    {
        public int Counter;
    }
```
- In Main add an object of the class TimerState timerState = new TimerState { Counter = 0 };
- Replace simple display with a call to TimerTask
```
T.Timer timerThreading = new T.Timer(new T.TimerCallback(TimerTask), timerState, 5000, 1000);
```
- Run it
Turning off the timer (0,5)
- Using timerThreading.Change(T.Timeout.Infinite, 0);
  Turn off timer after 5 calls (when the counter reaches 4)
Other timers .
Some libraries may contain their own timers:
- System.Windows.Forms.Timer: a Windows Forms component that triggers an event at regular intervals. The component has no user interface and is intended for use in a single-threaded environment.
- System.Web.UI.Timer: an ASP.NET component that performs asynchronous or synchronous web page callbacks at regular intervals.
- System.Windows.Threading.DispatcherTimer: a timer integrated into a queue that is processed at a specified interval and a Dispatcher with a specified priority.