.NET提供的CheckBox元件本身就支援三態按鈕（三種選取狀態），只要把屬性ThreeState設定為True即可
但有時候預設的外觀顯示與操作體驗可能無法準確呈現使用情境，這時可以新建一個類別繼承CheckBox並重載OnPaint與OnClick方法來客製化符合使用情境的三態按鈕
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| class CheckBoxTriState : CheckBox
{
public CheckBoxTriState()
{
ThreeState = true;
CheckState = System.Windows.Forms.CheckState.Indeterminate;
Text = String.Empty;
Size = new Size(20, 40);
}
protected override void OnPaint(PaintEventArgs pevent)
{
Graphics g = pevent.Graphics;
g.Clear(Color.LightGray);
Brush b = new SolidBrush(Color.DarkGray);
g.DrawRectangle(new Pen(b), 0, 0, Width, Height);
float radius = (float)(Width * 0.9);
float margin = (float)(Width * 0.05);
if (CheckState == System.Windows.Forms.CheckState.Indeterminate)
g.FillEllipse(b, margin, (float)(Height / 4.0) + margin, radius, radius);
else if (CheckState == System.Windows.Forms.CheckState.Checked)
g.FillEllipse(b, margin, margin, radius, radius);
else
g.FillEllipse(b, margin, (float)(Height / 2.0 - margin), radius, radius);
}
protected override void OnClick(EventArgs e)
{
Point pos = this.PointToClient(Cursor.Position);
if (pos.Y < Height / 3)
CheckState = System.Windows.Forms.CheckState.Checked;
else if (pos.Y > Height * 2 / 3)
CheckState = System.Windows.Forms.CheckState.Unchecked;
else
CheckState = System.Windows.Forms.CheckState.Indeterminate;
}
}
|
使用方始與一般的CheckBox相同
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| public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
CheckBoxTriState check = new CheckBoxTriState();
check.Location = new Point(10, 10);
Controls.Add(check);
CheckBoxTriState check2 = new CheckBoxTriState();
check2.Location = new Point(40, 10);
check2.CheckState = CheckState.Checked;
Controls.Add(check2);
CheckBoxTriState check3 = new CheckBoxTriState();
check3.Location = new Point(70, 10);
check3.CheckState = CheckState.Unchecked;
Controls.Add(check3);
}
}
|
Keyword：How to customize a tri-state checkbox / button in C#
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