How to make a UserControls BackColor transparent i

问题:

I created a simple stick man in a Windows Form User-Control (consisting of a radio button and three labels and one progress bar).

I set the back-color of the new user-control to transparent so that when I drag it onto my form, it blends with other colors and drawings on the form. I am not getting what I'm trying to achieve.

Here is the picture:

回答1:

UserControl already supports this, its ControlStyles.SupportsTransparentBackColor style flag is already turned on. All you have to do is set the BackColor property to Color.Transparent.

Next thing you have to keep in mind in that this transparency is simulated, it is done by asking the Parent of the control to draw itself to produce the background. So what is important is that you get the Parent set correctly. That's a bit tricky to do if the parent is not a container control. Like a PictureBox. The designer will make the Form the parent so you will see the form's background, not the picture box. You'll need to fix that in code, edit the form constructor and make it look similar to this:

var pos = this.PointToScreen(userControl11.Location);
userControl11.Parent = pictureBox1;
userControl11.Location = pictureBox1.PointToClient(pos);

回答2:

In constructor set style of control to support a transparent backcolor

SetStyle(ControlStyles.SupportsTransparentBackColor, true);

and then set Background to transperent color

this.BackColor = Color.Transparent;

From MSDN

A more complex approach (and possibly working one) is described here - with overrding of CreateParams and OnPaint.

回答3:

Why all those things? UserControl class has property Region. Set this to what ever shape you like and no other adjustments are needed.

public partial class TranspBackground : UserControl
{
    public TranspBackground()
    {
        InitializeComponent();
    }

    GraphicsPath GrPath
    {
        get
        {
            GraphicsPath grPath = new GraphicsPath();
            grPath.AddEllipse(this.ClientRectangle);
            return grPath;
        }
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        // set the region property to the desired path like this
        this.Region = new System.Drawing.Region(GrPath);

        // other drawing goes here
        e.Graphics.FillEllipse(new SolidBrush(ForeColor), ClientRectangle);
    }

}

The result is as in the image below:

No low level code, no tweaking, simple and clean. There is however one issue but in most cases it can go undetected, the edges are not smooth and anti-aliasing will not help either. But the workaround is fairly easy. In fact much easier than all those complex background handling..