[C#] Ứng dụng ví dụ Simple Observer Pattern tăng giảm số lượng trên winform

Vậy Observer Pattern là gì?

Hình ảnh demo.

Đầu tiên các bạn tạo cho mình một class IObserver.cs

public interface IObserver
{
    void Update(int count);
}

Tiếp theo một class ISubject.cs

public interface ISubject
{
    void RegisterObserver(IObserver observer);
    void UnregisterObserver(IObserver observer);
    void notifyObserver(int count);
}

Tiếp tục tạo một class Counter.cs để tăng giảm số lượng.

public class Counter : ISubject
{
	private List<IObserver> observers;
	private int count;

	public Counter()
	{
	    observers = new List<IObserver>();
	    count = 0;
	}

	public void Increment()
	{
	    count++;
	    notifyObserver(count);
	}

	public void Decrement()
	{
	    if (count > 0)
	    {
	        count--;
	        notifyObserver(count);
	    }
	        
	}
	    

	public void notifyObserver(int count)
	{
	    foreach (IObserver ob in observers)
	    {
	        ob.Update(count);
	    }
	}

	public void RegisterObserver(IObserver observer)
	{
	    observers.Add(observer);
	}

	public void UnregisterObserver(IObserver observer)
	{
	    observers.Remove(observer);
	}
}

Source code Form1.cs

public partial class Form1 : Form
{
    private Counter counter;
    public Form1()
    {
        counter = new Counter();
        InitializeComponent();
        var frm = new Form2(counter);
        frm.Show();
        counter.RegisterObserver(frm);

        var frmRect = new FrmRect(counter);
        frmRect.Show();
        counter.RegisterObserver(frmRect);
    }

    private void btnDecrement_Click(object sender, EventArgs e)
    {
        counter.Decrement();
    }

    private void btnIncrement_Click(object sender, EventArgs e)
    {
        counter.Increment();
    }
}

Source code Form2.cs

public partial class Form2 : Form, IObserver
{
    Counter counter1;
    public Form2(Counter counter)
    {
        InitializeComponent();
        this.counter1 = counter;
        this.FormClosing += Form2_FormClosing;
    }

    private void Form2_FormClosing(object sender, FormClosingEventArgs e)
    {
        counter1.UnregisterObserver(this);
    }

    public void Update(int count)
    {
        label1.Text = $"{count}";
    }
}

Và cuối cùng là source code cho Form3.cs

public partial class FrmRect : Form, IObserver
{
    Counter counter1;
    public FrmRect(Counter counter)
    {
        InitializeComponent();
        this.counter1 = counter;
        this.FormClosing += FrmRect_FormClosing;
    }

    private void FrmRect_FormClosing(object sender, FormClosingEventArgs e)
    {
        counter1.UnregisterObserver(this);
    }

    public void Update(int count)
    {
        updateRectange(count);
    }

    private void updateRectange(int count)
    {
        this.CreateGraphics().Clear(this.BackColor);
        SolidBrush solidBrush = new SolidBrush(Color.Red);
        Graphics graphics;
        graphics = this.CreateGraphics();
        graphics.FillRectangle(solidBrush, new Rectangle(0,0, count * 10, count *10));
        solidBrush.Dispose();
        graphics.Dispose();

    }
}

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