button click windows form c#

Question

Hi guys I'm trying to make a "minipaint" application which has three buttons(rectangle, circle and line). I'm having problem with making my buttons work. For example I have this rectangle class which inherits color, thickness, startpoints x, y from shape:

class rectangle : shape
{
    public int length { get; set; }
    public int width { get; set; }

    public override void Draw(Graphics g)
    {
        g.DrawRectangle(new Pen(color), new Rectangle(startx, starty, width, length));
    }
}

Now I want my rectangle_btn_Click to print a rectangle in my panel whenever I click on it. here is my panel code:

private void panel1_Paint(object sender, PaintEventArgs e)
{
    Graphics g = panel1.CreateGraphics();
}

and this is my button:

private void rectangle_btn_Click(object sender, EventArgs e)
{
    rectangle r = new rectangle();
    int retval = r.Draw(g);
}

But it has an error and it does not recognize g. How should I make this work?

Bojan B · Accepted Answer · 2016-11-08 09:49:42Z

3

You need to declare your Graphics object globally:

private Graphics g; 

private void panel1_Paint(object sender, PaintEventArgs e)
{
    g = panel1.CreateGraphics();
}

Then this should also work

private void rectangle_btn_Click(object sender, EventArgs e)
{
    rectangle r = new rectangle();
    r.Draw(g);
}

This assumes panel1_Paint and rectangle_btn_Click are both declared in the same class.

EDIT:

As @krw12572 pointed out the problem with this is that after minimizing the form the drawn object will disappear because the panel will be redrawn. To solve the problem following edits need to be made:

private List<shape> shapes = new List<shape>(); 

private void panel1_Paint(object sender, PaintEventArgs e)
{
    foreach (var shape in shapes) {
       shape.Draw(e.Graphics);
    }
}

private void button1_Click(object sender, EventArgs e) 
{   
    //This will however draw a rectangle at a fixed position with a fixed size         
    rectangle r = new rectangle() {startx = 10, starty = 10, length = 10, width = 10, color = Color.Black};
    shapes.Add(r);
    panel1.Invalidate();
}

Also the classes should look something like this:

public class shape
{
    public Color color { get; set; }
    public int width { get; set; }
    public int startx { get; set; }
    public int starty { get; set; }

    public virtual void Draw(Graphics g)
    {

    }
}

public class rectangle : shape
{
    public int length { get; set; }
    public int width { get; set; }
    public override void Draw(Graphics g)
    {
        g.DrawRectangle(new Pen(color), new Rectangle(startx, starty, width, length));
    }
}

This approach uses a cache with all objects that need to be drawn. On button click a object is added to the cache.

edited Nov 8, 2016 at 9:49

answered Nov 8, 2016 at 9:01

Bojan B

2,1214 gold badges20 silver badges26 bronze badges

Sign up to request clarification or add additional context in comments.

6 Comments

Sinatr Over a year ago

No dispose = bad.

Kamalesh Wankhede Over a year ago

This solution will fix syntax error and also draw rectangle but when panel1 is redrawn, that rectangle will disappear. Try minimizing and again maximizing application(after rectangle is drawn) to see what I'm talking about.

Bojan B Over a year ago

@krw12572 I update my answer considering your concerns. I also tested it out and it should work correctly even after minimizing and maximizing again.

Kamalesh Wankhede Over a year ago

Why do you need a global Graphics g;? You can use e.graphics from PaintEventArgs and call shape.Draw(e.Graphics).

Bojan B Over a year ago

You are right, there is no more need to have the Graphics global anymore. Tnx

|

Kamalesh Wankhede · Accepted Answer · 2016-11-08 09:40:39Z

1

You should perform any painting only in Paint event handler. Use graphics object from Paint event handler.

Implementing this way may be tricky but whenever your panel is redrawn, your painted shape will disappear if you don't perform painting in Paint event.

private shape _shape;

private void panel1_Paint(object sender, PaintEventArgs e)
{
    _shape.Draw(e.Graphics);
}

private void rectangle_btn_Click(object sender, EventArgs e)
{
    _shape = new rectangle();
    panel1.Invalidate();
}

Update: Above answer is assuming you have Draw(Graphics g) method in your base class shape and it's overridden/implemented in rectangle class.

edited Nov 8, 2016 at 9:40

answered Nov 8, 2016 at 9:04

Kamalesh Wankhede

1,50516 silver badges40 bronze badges

2 Comments

sara Over a year ago

it has "can't assign to Draw because it is a mehod group" error for the line _shape.Draw(e.Graphics);

Kamalesh Wankhede Over a year ago

That's because your Draw method is not written in shape class. Now, instead of private shape _shape; try private rectangle _shape;. That should work.

Shanav Asija · Accepted Answer · 2016-11-08 09:03:02Z

0

You should either declare your Graphics variable 'g' inside rectangle_btn_click or at the class level outside any methods scope. Then use it inside your stubs.

answered Nov 8, 2016 at 9:03

Shanav Asija

213 bronze badges

Collectives™ on Stack Overflow

button click windows form c#

3 Answers 3

6 Comments

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

6 Comments

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related