Changing colours using a combo box in Windows Form App

Question

protected override void OnPaint(PaintEventArgs e)
{
    if (comboBox1.Text == "Circle")
    {
        e.Graphics.FillEllipse(Brushes.Red, new Rectangle(105, 120, 64, 64));
    }

    if (comboBox1.Text == "Rectangle")
    {
        e.Graphics.FillRectangle(Brushes.Red, new Rectangle(105, 120, 75, 50));
    }

    if(comboBox1.Text == "Triangle")
    {
        Point[] points = { new Point(140, 110), new Point(230, 190), new Point(50, 190) };
        e.Graphics.FillPolygon(Brushes.Red, points);
    }
}

I've created these shapes above and they're within a combo box so but I'm trying to get it so my second combo box will change the color of the shape, is there any way to do this? I can't seem to find it anywhere. The second combo box contains Red, Green, Blue, Custom Colour. I have it so the colour palette comes up but I don't know how to set it to the shape when selected either.

How would I reference the shapes and change the brush color is the part I'm struggling with

You just need to populate the 2nd combobix by iterating over System.Drawing.Colors then use the selected colour in the OnPaint() — Jeremy Thompson, Feb 14 '18 at 09:55
Use the tags please. Many UIs have combo boxes: WPF/WebForms/WinForms/XamarinForms/WinRT/etc. — György Kőszeg, Feb 14 '18 at 09:56
Along with combobox1 you also need to check what is selected in combobox2 and based on that you need to apply appropriate brush — Chetan, Feb 14 '18 at 09:58
You'll have to create the appropriate brush to paint with. So instead of Brushes.Red, you need to use the [SolidBrush constructor](https://msdn.microsoft.com/en-us/library/system.drawing.solidbrush.solidbrush(v=vs.110).aspx) with the selected color. — Hans Passant, Feb 14 '18 at 10:44

score 1 · Accepted Answer · answered Feb 26 '18 at 11:19

May be outdated but just to simplify your code and make it clearer you can use a switch statement

 if ((comboBox1.Text != defaultTextShape) && (comboBox2.Text != defaultTextColour))
        {
            Brush b;
            switch (comboBox1.Text)
            {
                case "Red"   : b = Brushes.Red; break;
                case "Green" : b = Brushes.Green; break;
                case "Blue"  : b = Brushes.Blue; break;
                default      : b = new SolidBrush(CustomColour); break;
            }

            switch (comboBox2.Text)
            {
                case "Rectangle": e.Graphics.FillRectangle(b, new Rectangle(105, 120, 75, 50)); break;
                case "Circle"   : e.Graphics.FillEllipse(b, new Rectangle(105, 120, 64, 64)); break;                    
                default:
                    Point[] points = { new Point(140, 110), new Point(230, 190), new Point(50, 190) };
                    e.Graphics.FillPolygon(b, points); break;
            }


        }

Custom colour is a public const which assigns your Custom colour picker value to it and then assigns it to B

Mong Zhu · Answer 2 · 2018-02-14T12:57:31.143

As Hans Passant already pointed out: You need to use the SolidBrush object to set the custom colour. This is described in the Post convert from Color to brush.

In your case I would populate the colour ComboBox the following way:

comboBox_Colour.DataSource = new List<Color> { Color.Red, Color.Blue, Color.Yellow, Color.Green };

Now in the OnPaint event you can check whether any items are chosen already and then grab the Color directly from the SelectedItem of comboBox_Colour. Then you plug it into the constructor of a SolidBrush object and feed the SolidBrush to Fill... methods. It will work because SolidBrush inherits from Brush

public sealed class SolidBrush : Brush

protected override void OnPaint(PaintEventArgs e)
{
    if (comboBox_Shape.SelectedIndex != -1 && comboBox_Colour.SelectedIndex != -1)
    {
        Color c = (Color)comboBox_Colour.SelectedItem;
        SolidBrush sb = new SolidBrush(c);
        if (comboBox_Shape.Text == "Circle")
        {
            e.Graphics.FillEllipse(sb, new Rectangle(105, 120, 64, 64));
        }
        else if (comboBox_Shape.Text == "Rectangle")
        {
            e.Graphics.FillRectangle(sb, new Rectangle(105, 120, 75, 50));
        }
        else if (comboBox_Shape.Text == "Triangle")
        {
            Point[] points = { new Point(140, 110), new Point(230, 190), new Point(50, 190) };
            e.Graphics.FillPolygon(sb, points);
        }
    }
}

EDIT:

If the choice of colours that I provided here is not sufficient for you you can dump all colours that the struct Color has to offer into the comboBox_Colour:

List<Color> allColours = typeof(Color).GetProperties(
                     System.Reflection.BindingFlags.Static | 
                     System.Reflection.BindingFlags.Public)
                    .Select(x => (Color)x.GetValue(null)).ToList();

comboBox_Colour.DataSource = allColours;

@Twyxz Glad to hear. You are welcome. Was a fun problem to solve :) — Mong Zhu, Feb 14 '18 at 13:15
Is it possible for the colour to be selected from a Colour palette? Rather than the list of colours @MongZhu — Twyxz, Feb 14 '18 at 13:25
@Twyxz everything is possible ;) you need the [ColorDialog](https://msdn.microsoft.com/en-us/library/system.windows.forms.colordialog(v=vs.110).aspx) class. Try it. Tt is not very complex. If you have difficulties then you can ask a new question and poke me again ;) I will answer it good luck — Mong Zhu, Feb 14 '18 at 14:04

Changing colours using a combo box in Windows Form App

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