[C#] チェックボックスの色を変更する方法

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox customCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeCustomCheckBox();
	}
	private void InitializeCustomCheckBox()
	{
		customCheckBox = new CheckBox();
		customCheckBox.Text = "カスタムチェックボックス";
		customCheckBox.Location = new Point(20, 20);
		customCheckBox.Size = new Size(150, 30);
		customCheckBox.Appearance = Appearance.Button;
		customCheckBox.FlatStyle = FlatStyle.Flat;
		customCheckBox.Paint += new PaintEventHandler(CustomCheckBox_Paint);
		this.Controls.Add(customCheckBox);
	}
	private void CustomCheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		if (cb.Checked)
		{
			e.Graphics.FillRectangle(Brushes.Red, cb.ClientRectangle);
		}
		else
		{
			e.Graphics.FillRectangle(Brushes.Green, cb.ClientRectangle);
		}
		e.Graphics.DrawString(cb.Text, cb.Font, Brushes.White, new PointF(5, 5));
	}
}

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox customCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeCustomCheckBox();
	}
	private void InitializeCustomCheckBox()
	{
		customCheckBox = new CheckBox();
		customCheckBox.Text = "カスタムチェックボックス";
		customCheckBox.Location = new Point(20, 20);
		customCheckBox.Size = new Size(150, 30);
		customCheckBox.Paint += new PaintEventHandler(CustomCheckBox_Paint);
		this.Controls.Add(customCheckBox);
	}
}

private void CustomCheckBox_Paint(object sender, PaintEventArgs e)
{
    CheckBox cb = sender as CheckBox;
    Graphics g = e.Graphics;
    // 背景色を設定
    if (cb.Checked)
    {
        g.FillRectangle(Brushes.Red, cb.ClientRectangle);
    }
    else
    {
        g.FillRectangle(Brushes.Green, cb.ClientRectangle);
    }
    // 前景色を設定
    g.DrawString(cb.Text, cb.Font, Brushes.White, new PointF(5, 5));
}

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox customCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeCustomCheckBox();
	}
	private void InitializeCustomCheckBox()
	{
		customCheckBox = new CheckBox();
		customCheckBox.Text = "赤い背景のチェックボックス";
		customCheckBox.Location = new Point(20, 20);
		customCheckBox.Size = new Size(200, 30);
		customCheckBox.Paint += new PaintEventHandler(CustomCheckBox_Paint);
		this.Controls.Add(customCheckBox);
	}
	private void CustomCheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		e.Graphics.FillRectangle(Brushes.Red, cb.ClientRectangle);
		e.Graphics.DrawString(cb.Text, cb.Font, Brushes.White, new PointF(5, 5));
	}
}

チェックボックスの背景が常に赤色に塗りつぶされ、テキストは白色で表示されます。

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox customCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeCustomCheckBox();
	}
	private void InitializeCustomCheckBox()
	{
		customCheckBox = new CheckBox();
		customCheckBox.Text = "青いテキストのチェックボックス";
		customCheckBox.Location = new Point(20, 60);
		customCheckBox.Size = new Size(200, 30);
		customCheckBox.Paint += new PaintEventHandler(CustomCheckBox_Paint);
		this.Controls.Add(customCheckBox);
	}
	private void CustomCheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		e.Graphics.FillRectangle(SystemBrushes.Control, cb.ClientRectangle);

		var brush = Brushes.Blue;

		if (cb.Checked)
		{
			brush = Brushes.Red;
		}

		e.Graphics.DrawString(cb.Text, cb.Font, brush, new PointF(5, 5));
	}
}

チェックボックスのテキストが青色で表示され、背景はデフォルトの色になります。

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox customCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeCustomCheckBox();
	}
	private void InitializeCustomCheckBox()
	{
		customCheckBox = new CheckBox();
		customCheckBox.Text = "カスタム枠線のチェックボックス";
		customCheckBox.Location = new Point(20, 100);
		customCheckBox.Size = new Size(200, 30);
		customCheckBox.Paint += new PaintEventHandler(CustomCheckBox_Paint);
		this.Controls.Add(customCheckBox);
	}
	private void CustomCheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		e.Graphics.FillRectangle(SystemBrushes.Control, cb.ClientRectangle);
		e.Graphics.DrawRectangle(Pens.Black, 0, 0, cb.Width - 1, cb.Height - 1);
		e.Graphics.DrawString(cb.Text, cb.Font, Brushes.Black, new PointF(5, 5));
	}
}

チェックボックスの周囲に黒い枠線が描画され、テキストは黒色で表示されます。

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox stateCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeStateCheckBox();
	}
	private void InitializeStateCheckBox()
	{
		stateCheckBox = new CheckBox();
		stateCheckBox.Text = "状態に応じた色変更";
		stateCheckBox.Location = new Point(20, 20);
		stateCheckBox.Size = new Size(200, 30);
		stateCheckBox.Paint += new PaintEventHandler(StateCheckBox_Paint);
		this.Controls.Add(stateCheckBox);
	}
	private void StateCheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		if (cb.Checked)
		{
			e.Graphics.FillRectangle(Brushes.LightGreen, cb.ClientRectangle);
		}
		else
		{
			e.Graphics.FillRectangle(Brushes.LightCoral, cb.ClientRectangle);
		}
		e.Graphics.DrawString(cb.Text, cb.Font, Brushes.Black, new PointF(5, 5));
	}
}

チェックボックスがチェックされているときは背景がライトグリーン になり、チェックされてイベントが発生するときはライトコーラルになります。

using System.Drawing;
using System.Windows.Forms;

public partial class MyForm : Form
{
	private CheckBox[] checkBoxes;
	public MyForm()
	{
		InitializeComponent();
		InitializeCheckBoxes();
	}
	private void InitializeCheckBoxes()
	{
		checkBoxes = new CheckBox[3];
		for (int i = 0; i < checkBoxes.Length; i++)
		{
			checkBoxes[i] = new CheckBox();
			checkBoxes[i].Text = $"チェックボックス {i + 1}";
			checkBoxes[i].Location = new Point(20, 20 + i * 40);
			checkBoxes[i].Size = new Size(200, 30);
			checkBoxes[i].Paint += new PaintEventHandler(CheckBox_Paint);
			this.Controls.Add(checkBoxes[i]);
		}
	}
	private void CheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		e.Graphics.FillRectangle(Brushes.LightBlue, cb.ClientRectangle);
		e.Graphics.DrawString(cb.Text, cb.Font, Brushes.Black, new PointF(5, 5));
	}
}

フォーム上のすべてのチェックボックスがライトブルーの背景色で表示されます。

using System.Drawing;
using System.Windows.Forms;
using System;

public partial class MyForm : Form
{
	private CheckBox dynamicCheckBox;
	public MyForm()
	{
		InitializeComponent();
		InitializeDynamicCheckBox();
	}
	private void InitializeDynamicCheckBox()
	{
		dynamicCheckBox = new CheckBox();
		dynamicCheckBox.Text = "動的に色を変更";
		dynamicCheckBox.Location = new Point(20, 20);
		dynamicCheckBox.Size = new Size(200, 30);
		dynamicCheckBox.CheckedChanged += new EventHandler(DynamicCheckBox_CheckedChanged);
		dynamicCheckBox.Paint += new PaintEventHandler(DynamicCheckBox_Paint);
		this.Controls.Add(dynamicCheckBox);
	}
	private void DynamicCheckBox_CheckedChanged(object sender, EventArgs e)
	{
		dynamicCheckBox.Invalidate(); // 再描画を要求
	}
	private void DynamicCheckBox_Paint(object sender, PaintEventArgs e)
	{
		CheckBox cb = sender as CheckBox;
		if (cb.Checked)
		{
			e.Graphics.FillRectangle(Brushes.Yellow, cb.ClientRectangle);
		}
		else
		{
			e.Graphics.FillRectangle(Brushes.Gray, cb.ClientRectangle);
		}
		e.Graphics.DrawString(cb.Text, cb.Font, Brushes.Black, new PointF(5, 5));
	}
}

チェックボックスの状態が変化するたびに、背景色が黄色または灰色に動的に変更されます。