我们先来看看IssueVision中一个用户控件PaneCaption在可视化设计器中的属性窗口.

    再看一下在另一个用户控件StaffPane中使用它时的属性窗口:

    大家会发现它多出来很多个属性,这些属性是原来继承控件中没有的属性,如:InactiveTextColor,InactiveTextColor等等.它们是如何实现的呢?我们就来看一下这个用户控件的代码PaneCaption.cs吧.

namespace IssueVision
{
 // Custom control that draws the caption for each pane. Contains an active
 // state and draws the caption different for each state. Caption is drawn
 // with a gradient fill and antialias font.
 public class PaneCaption : UserControl
 {
  private class Consts
  {
 ......

  可以看到它是由 System.Windows.Forms.UserControl 继承而来,图一显示了它的默认属性.下面我们接着PaneCaption.cs代码,看看是如何将属性或事件显示在可视化设计器中.

  [DefaultValueAttribute(typeof(Color), "3, 55, 145")]
  [DescriptionAttribute("Low color of the inactive gradient.")]
  [CategoryAttribute("Appearance")]
  public Color InactiveGradientLowColor
  {
   get
   {
    return m_colorInactiveLow;
   }

   set
   {
    if (value == Color.Empty)
    {
     value = Color.FromArgb(3, 55, 145);
    }
    m_colorInactiveLow = value;
    CreateGradientBrushes();  //自定义方法,用于创建线形渐变笔刷
    Invalidate();    //Control.Invalidate 方法,使控件的特定区域无效并向控件发送绘制消息
   }
  }

  [CategoryAttribute("Appearance")]
  [DescriptionAttribute("High color of the inactive gradient.")]
  [DefaultValueAttribute(typeof(Color), "90, 135, 215")]
  public Color InactiveGradientHighColor
  {
   get
   {
    return m_colorInactiveHigh;
   }

   set
   {
    if (value == Color.Empty)
    {
     value = Color.FromArgb(90, 135, 215);
    }
    m_colorInactiveHigh = value;
    CreateGradientBrushes();
    Invalidate();
   }
  }

  [DescriptionAttribute("Text displayed in the caption.")]
  [DefaultValueAttribute("")]
  [CategoryAttribute("Appearance")]
  public string Caption
  {
   get
   {
    return m_text;
   }

   set
   {
    m_text = value;
    Invalidate();
   }
  }

  其结果如下图所示:

    我们可以看到Views,Staff list背景都是使用这个自定义的PaneCaption产生渐变效果(由InactiveGradientHighColor和InactiveGradientLowColor属性实现),文字Views和Staff list是由属性Caption实现.

    我们看到举例的这三个属性CategoryAttribute属性值都为CategoryAttribute("Appearance"),从图二可以看出,这些属性都显示在"外观"下.

    DefaultValueAttribute 属性顾名思义,就是此自定义属性的默认值.
    DescriptionAttribute 属性则为此自定义属性的描述.


    关键部分已经设置完成,剩下的就是如何实现属性的效果了,我以代码说明:

 protected override void OnPaint(PaintEventArgs e)
  {
   DrawCaption(e.Graphics);
   base.OnPaint(e);
  }

  // draw the caption
  private void DrawCaption(Graphics g)
  {
   // background
   g.FillRectangle(this.BackBrush, this.DisplayRectangle);
   
   if (m_antiAlias)
    g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;
   
   // need a rectangle when want to use ellipsis
   RectangleF bounds  = new RectangleF(Consts.PosOffset,
            0,
            this.DisplayRectangle.Width - Consts.PosOffset,
            this.DisplayRectangle.Height);

   g.DrawString(m_text, this.Font, this.TextBrush, bounds, m_format);
  }

 使用Graphics.DrawString 绘制出Caption(即文字Views和Staff list),Graphics.FillRectangle 绘制渐变背景.注意此Graphics.FillRectangle 方法的第一个参数为笔刷,此笔刷就为上面自定义属性代码中CreateGradientBrushes() 方法所创建的笔刷.代码如下:

 private void CreateGradientBrushes()
  {
   // can only create brushes when have a width and height
   if (Width > 0 && Height > 0)
   {
    if (m_brushActive != null)
    {
     m_brushActive.Dispose();
    }
  // 其中  m_colorActiveHigh 值就为自定义属性InactiveGradientHighColor的值,m_colorActiveLow则为自定义属性InactiveGradientLowColor的值.
    m_brushActive = new LinearGradientBrush(DisplayRectangle, m_colorActiveHigh, m_colorActiveLow, LinearGradientMode.Vertical);
    
    if (m_brushInactive != null)
    {
     m_brushInactive.Dispose();
    }
    
    m_brushInactive = new LinearGradientBrush(DisplayRectangle, m_colorInactiveHigh, m_colorInactiveLow, LinearGradientMode.Vertical);
   }
  }

// gradient brush for the background
  private LinearGradientBrush BackBrush
  {
   get
   {
    if (m_active && m_allowActive)
     return m_brushActive;
    else
     return m_brushInactive;
   }
  }

 补充一点:根据GDI+要求,所有图形的绘制都通过OnPaint()方法绘制,只用重载此方法,就可以重新绘制所需的图形了.(此方法就如Java中的PaintComponet()方法一样)

  这次就写这么多了,希望大家多多交流,这也只是我一个人的认识,还要多和大家交流才会有提高.



CopyRight © YellowWee 2004. All Right Reserved.