Getting Form coordinates within class

Question

Basically I have created a Class with a method that is called everytime there is a click on my form(it is supposed to draw a single line where I clicked) it goes as follows:

public void Dessiner(Graphics Fg)
{

    Point p = Form1.MousePosition;
    Fg.DrawLine(MyPen,p.X,p.Y,p.X+2,p.Y+2);
}

The problem is when I call this method within my Forms' mousedown event it places the line at the wrong spot everytime.

Notes: the method can only take the graphics Fg, and the drawing of the line MUST be done within the method of the class.

What am I doing wrong?

Sorry about that Fg is the instance of my graphics that was declared in my form: — Fylps, Dec 03 '15 at 00:35
Fg is the instance of my graphics class that I created in my form so basically (within the form) Fg=this.createGraphics(); and it is used as the parameter for my method afterwards. — Fylps, Dec 03 '15 at 00:36
Lets say i click in the middle of the Form it will put the line an inch lower to the right, but the change is relatively random — Fylps, Dec 03 '15 at 00:39
The drawing is done directly on the form(which contains a menu bar if that changes anything) — Fylps, Dec 03 '15 at 00:43
Note that [MousePosition](https://msdn.microsoft.com/en-us/library/system.windows.forms.control.mouseposition(v=vs.110).aspx) returns the result in screen (not form) relative coordinates. — 500 - Internal Server Error, Dec 03 '15 at 00:56
Yeah I realised that but I couldnt find another way of getting any type of coordinate. — Fylps, Dec 03 '15 at 00:58
convert the MousePosition to control position using form.PointToClient(...) — smertrios, Dec 03 '15 at 01:05
The problem is I cant seem to be able to access PointToClient() within my method. I try to call Form1.PointToClient but get nothing, only option that makes sense in those given is MousePosition. — Fylps, Dec 03 '15 at 01:07
Also your Form1 object is the default instance of your form, it is **not** the form you are looking at, you will need to pass in your actual form object. — Mark Hall, Dec 03 '15 at 01:08
Ok thats what ive seen but cant seem to understand, how can I get any type of handle for a form that is only create at the beginning of the program? — Fylps, Dec 03 '15 at 01:10
Your MouseDown event handler's `e` argument has information about the coordinate of the event in its properties `X` and `Y`. — 500 - Internal Server Error, Dec 03 '15 at 01:14
Just add another parameter to your method, either pass in the Form instance or the mouse coordinates like @500-InternalServerError suggests. — Mark Hall, Dec 03 '15 at 01:16
I know i could do that but I specified that the method could only take the instance of Graphics as parameter no other. Also how would i access the event handler e from within the method of my class? — Fylps, Dec 03 '15 at 01:22
you said that the method is "called everytime there is a click" on the form. so why can't you pass it the click event args? It'd probably help if you give us more code context. — smertrios, Dec 03 '15 at 01:42
I am restricted by a rule where as the method from my class can only accept as a parameter the Grahphics Fg, nothing else and the drawing of the line must be done within this method. — Fylps, Dec 03 '15 at 01:48
Is this class initialized in your form? If so is it permissible with the restrictions that you are specifying to create a constructor and pass in the instance of the owner/parent form to it when your class is initialized. That way your class will have knowledge of your Form. — Mark Hall, Dec 03 '15 at 01:50

score 1 · Accepted Answer · answered Dec 03 '15 at 02:01

You need to transform the coordinates with PointToClient()

public partial class Form1 : Form
{
    DrawingHelper dh;
    public Form1()
    {
        InitializeComponent();

        dh=new DrawingHelper(this);

    }

    private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        dh.Desser(this.CreateGraphics());
    }
}

public class DrawingHelper
{
    Form form;
    public DrawingHelper(Form form)
    {
        this.form  =form;
    }
    public void Desser(Graphics Fg)
    {
        var pt=form.PointToClient(Form.MousePosition);
        Fg.DrawLine(Pens.Black, pt.X,pt.Y, pt.X+2, pt.Y+2);
    }
}

Thanks so much for the help I never completely understood how to use the current form! Great help from all!!! — Fylps, Dec 03 '15 at 02:09

Getting Form coordinates within class

1 Answers1