How to hide System.Drawing line with condition

Question

How to hide System.Drawing line with condition:

    System.Drawing.Pen myPen;            
    myPen = new System.Drawing.Pen(System.Drawing.Color.White);           
    System.Drawing.Graphics formGraphics = this.CreateGraphics();

    formGraphics.DrawLine(myPen, 108, 272, 153, 160);  

    myPen.Dispose();
    formGraphics.Dispose();

I want to hide the drawn line formGraphics.DrawLine(myPen, 108, 272, 153, 160); with condition if (x > 1) {} else if (x = 1) {} display it again

Answer 1

Subscribe to the Form.Paint event, either through the designer or in the form constructor. Then in the paint event handler do the conditional drawing. Also make your x variable into a property (public or private) and call Invalidate on the form when it changes. This will cause the form to be redrawing, calling the paint event.

private int x = 0;

public int X
{
    get
    {
        return x;
    }

    set
    {
        x = value;
        // Cause the form to be redrawn.
        this.Invalidate();
    }
}

private void Form1_Paint(object sender, PaintEventArgs e)
{
    e.Graphics.Clear(Color.Black);

    // Only draw the line if x == 1.
    if (x == 1)
    {
        e.Graphics.DrawLine(Pens.White, 108, 272, 153, 160);
    }
}