如何通过单击按钮更改线条的颜色？

Question

I am able to change colour of a line,like this:-

Pen P1 = new Pen(Color.Blue, 3);
PointF pt1 = new PointF(450.0F, 60.0F);
PointF pt2 = new PointF(20.0F, 60.0F);
e.Graphics.DrawLine(P1, pt1, pt2);

But, I am not able to change the colour of a line with a button's click.

Please tell how to change the colour of a line with click of a button, in windows form, visual studio, in c#.

Answer 1

Create a field of type Pen and initialize its Color to color you want and in Button 's Click event handler, change the color of the pen and Invalidate the client area of the Form to trigger a paint event.

public partial class Form1: Form
{
    public Form1()
    {
        SetStyle(ControlStyles.AllPaintingInWmPaint | ControlStyles.OptimizedDoubleBuffer | ControlStyles.UserPaint, true);
        InitializeComponent();
        m_pen = new Pen(Color.Black, 2.0f);
    }
    private Pen m_pen = null;
    
    protected override void OnPaint(PaintEventArgs e)
    {
         base.OnPaint(e);
         e.Graphics.DrawLine(m_pen, 0, 0, 100, 100);
    }
    private void button1_Click(object sender, EventArgs e)
    {
         m_pen.Color = Color.Blue;
         Invalidate(); 
    }
 
}