Draw focus selection box

Recently, I want to prepare a custom control for a project. I need to know more about drawing. Fortunately, the codeproject has such an article drawtools, it provides me with a lot of sample code to learn.

The draw focus selection box for the first thing to learn.

I thought it would be like drawing a box to draw, and I don't want GDI to have a special method for use.

Controlpaint. drawfocusrectangle (E. Graphics, this. focusrectangle, color. Black, color. Transparent );

The following is part of the code for the usercontrol of the responsibility plotting work.

Code generated by the component designer # code generated by the region component designer
/** // <Summary>
/// The designer supports the required methods-do not use the code editor
/// Modify the content of this method.
/// </Summary>
Private void initializecomponent ()
{
// Omit Part of the Code
This. mouseup + = new system. Windows. Forms. mouseeventhandler (this. drawarea_mouseup );
This. Paint + = new system. Windows. Forms. painteventhandler (this. drawarea_paint );
This. mousemove + = new system. Windows. Forms. mouseeventhandler (this. drawarea_mousemove );
This. mousedown + = new system. Windows. Forms. mouseeventhandler (this. drawarea_mousedown );
This. resumelayout (false );

}
# Endregion

Private point startpoint;
Private rectangle focusrectangle;
Private bool bdrawfocusrectangle;

Public void Init (bool isfill)
{
Setstyle (controlstyles. allpaintinginwmpaint |
Controlstyles. userpaint | controlstyles. doublebuffer, true );
If (isfill)
This. Dock = dockstyle. Fill;
}

/** // <Summary>
/// Obtain the drawn box.
/// We may choose from left to right, from top to bottom, or from bottom to top, from right to left.
/// Some programs need to be judged.
/// </Summary>
/// <Param name = "X1"> </param>
/// <Param name = "Y1"> </param>
/// <Param name = "X2"> </param>
/// <Param name = "Y2"> </param>
/// <Returns> </returns>
Public static rectangle getnormalizedrectangle (INT X1, int Y1, int X2, int Y2)
{
If (X2 <X1)
{
Int TMP = x2;
X2 = x1;
X1 = TMP;
}

If (Y2 <Y1)
{
Int TMP = Y2;
Y2 = Y1;
Y1 = TMP;
}

Return new rectangle (x1, Y1, x2-X1, Y2-Y1 );
}

Private void drawarea_mousemove (Object sender, system. Windows. Forms. mouseeventargs E)
{
If (E. Button = mousebuttons. Left)
{
This. bdrawfocusrectangle = true;
This. focusrectangle = drawarea. getnormalizedrectangle (this. startpoint. X, this. startpoint. Y, E. X, E. y );
This. Refresh (); // redraw
}
}

Private void drawarea_mousedown (Object sender, system. Windows. Forms. mouseeventargs E)
{
This. startpoint = new point (E. X, E. y );
}

Private void drawarea_paint (Object sender, system. Windows. Forms. painteventargs E)
{
If (this. bdrawfocusrectangle)
Controlpaint. drawfocusrectangle (E. Graphics, this. focusrectangle, color. Black, color. Transparent );
}

Private void drawarea_mouseup (Object sender, system. Windows. Forms. mouseeventargs E)
{
This. bdrawfocusrectangle = false;
This. Refresh ();
}

Use this control in Form

Private void form1_load (Object sender, system. eventargs E)
{
This. drawarea1.init (true );
}