调试易

public partial class UserControl1 : Form
    {
        public UserControl1()
        {
            InitializeComponent();
        }        private void UserControl1_Load(object sender, EventArgs e)
        {        }
    }
将自定义控件继承Form的基类就可以有Opacity属性  就可以让控件透明

那样此控件就不是控件了 而是form了

 SetStyle(
               ControlStyles.UserPaint |
               ControlStyles.AllPaintingInWmPaint |
               ControlStyles.OptimizedDoubleBuffer |
               ControlStyles.SupportsTransparentBackColor |
               ControlStyles.Selectable |
               ControlStyles.ResizeRedraw, true);

IUControl.cs控件代码： 
public partial class IUControl: UserControl
    {
public IUControl()
        {
            InitializeComponent();
            SetStyle(
             ControlStyles.UserPaint |
             ControlStyles.AllPaintingInWmPaint |
             ControlStyles.OptimizedDoubleBuffer |
             ControlStyles.SupportsTransparentBackColor |
             ControlStyles.Selectable |
             ControlStyles.ResizeRedraw, true);
        }
}
应用控件的页面代码            this.iuControl= new IUControl();
            this.Controls.Add(this.iuControl);
            this.iuControl.AutoSize = true;
            this.iuControl.Location = new System.Drawing.Point(65, 193);
            this.iuControl.Name = "iuCompass";
            this.iuControl.Size = new System.Drawing.Size(250,250);            
            this.iuControl.Text = "我的控件";            iuControl.BackColor = System.Drawing.Color.Transparent;
但运行iuControl背景还是灰色的！

this.BackColor = Color.Transparent; //这条语句加在控件代码中
this.AllowTransparency = true;         //这句代码加到form的代码里

Protected Overrides ReadOnly Property CreateParams() As CreateParams
    Get
        Dim cParms As CreateParams = MyBase.CreateParams
        cParms.ExStyle = cParms.ExStyle Or &H80000
        ' WS_EX_LAYERED 
        Return cParms
    End Get
End Property