浅谈Winform控件开发（一）：使用GDI+美化基础窗口

时间:2021-02-05 __Meow 人气:0

写在前面：
本系列第一篇内容将仅包含对于Winform基础窗口也就是System.Windows.Forms.Form的美化，后续将对一些常用控件如Button、ComboBox、CheckBox、TextBox等进行修改，并提供一些其他如Loading遮罩层等常见控件。
对于基础窗口的美化，首要的任务就是先把基础标题栏干掉。这个过程中会涉及一些Windows消息机制。

首先，我们新建一个类XForm，派生自System.Windows.Forms.Form。

1 /// <summary>
2 /// 表示组成应用程序的用户界面的窗口或对话框。
3 /// </summary>
4 [ToolboxItem(false)]
5 public class XForm : Form
6 ...

随后，我们定义一些常量

 1 /// <summary>
 2 /// 标题栏高度
 3 /// </summary>
 4 public const int TitleBarHeight = 30;
 5 
 6 // 边框宽度
 7 private const int BorderWidth = 4;
 8 // 标题栏图标大小
 9 private const int IconSize = 16;
10 // 标题栏按钮大小
11 private const int ButtonWidth = 30;
12 private const int ButtonHeight = 30;

覆盖基类属性FormBorderStyle使base.FormBorderStyle保持None，覆盖基类属性Padding返回或设置正确的内边距

 1 /// <summary>
 2 /// 获取或设置窗体的边框样式。
 3 /// </summary>
 4 [Browsable(true)]
 5 [Category("Appearance")]
 6 [Description("获取或设置窗体的边框样式。")]
 7 [DefaultValue(FormBorderStyle.Sizable)]
 8 public new FormBorderStyle FormBorderStyle
 9 {
10     get => _formBorderStyle;
11     set
12     {
13         _formBorderStyle = value;
14         UpdateStyles();
15         DrawTitleBar();
16     }
17 }
18 
19 /// <summary>
20 /// 获取或设置窗体的内边距。
21 /// </summary>
22 [Browsable(true)]
23 [Category("Appearance")]
24 [Description("获取或设置窗体的内边距。")]
25 public new Padding Padding
26 {
27     get => new Padding(base.Padding.Left, base.Padding.Top, base.Padding.Right, base.Padding.Bottom - TitleBarHeight);
28     set => base.Padding = new Padding(value.Left, value.Top, value.Right, value.Bottom + TitleBarHeight);
29 }

※最后一步也是最关键的一步：重新定义窗口客户区边界。重写WndProc并处理WM_NCCALCSIZE消息。

 1 protected override void WndProc(ref Message m)
 2 {
 3     switch (m.Msg)
 4     {
 5             case WM_NCCALCSIZE:
 6             {
 7                 // 自定义客户区
 8                 if (m.WParam != IntPtr.Zero && _formBorderStyle != FormBorderStyle.None)
 9                 {
10                     NCCALCSIZE_PARAMS @params = (NCCALCSIZE_PARAMS)
11                         Marshal.PtrToStructure(m.LParam, typeof(NCCALCSIZE_PARAMS));
12                     @params.rgrc[0].Top += TitleBarHeight;
13                     @params.rgrc[0].Bottom += TitleBarHeight;
14                     Marshal.StructureToPtr(@params, m.LParam, false);
15                     m.Result = (IntPtr)(WVR_ALIGNTOP | WVR_ALIGNBOTTOM | WVR_REDRAW);
16                 }
17 
18                 base.WndProc(ref m);
19                 break;
20             }
21 ……

相关常量以及P/Invoke相关方法已在我的库中定义，详见MSDN，也可从http://pinvoke.net/查询。
同样在WndProc中处理WM_NCPAINT消息

1 case WM_NCPAINT:
2 {
3     DrawTitleBar();
4     m.Result = (IntPtr)1;
5     break;
6 }

DrawTitleBar()方法定义如下：

 1 /// <summary>
 2 /// 绘制标题栏
 3 /// </summary>
 4 private void DrawTitleBar()
 5 {
 6     if (_formBorderStyle == FormBorderStyle.None)
 7         return;
 8 
 9     DrawTitleBackgroundTextIcon();
10     CreateButtonImages();
11     DrawTitleButtons();
12 }

首先使用线性渐变画刷绘制标题栏背景、图标、标题文字：

 1 /// <summary>
 2 /// 绘制标题栏背景、文字、图标
 3 /// </summary>
 4 private void DrawTitleBackgroundTextIcon()
 5 {
 6     IntPtr hdc = GetWindowDC(Handle);
 7     Graphics g = Graphics.FromHdc(hdc);
 8 
 9     // 标题栏背景
10     using (Brush brsTitleBar = new LinearGradientBrush(TitleBarRectangle,
11         _titleBarStartColor, _titleBarEndColor, LinearGradientMode.Horizontal))
12         g.FillRectangle(brsTitleBar, TitleBarRectangle);
13 
14     // 标题栏图标
15     if (ShowIcon)
16         g.DrawIcon(Icon, new Rectangle(
17             BorderWidth, TitleBarRectangle.Top + (TitleBarRectangle.Height - IconSize) / 2,
18             IconSize, IconSize));
19 
20     // 标题文本
21     const int txtX = BorderWidth + IconSize;
22     SizeF szText = g.MeasureString(Text, SystemFonts.CaptionFont, Width, StringFormat.GenericDefault);
23     using Brush brsText = new SolidBrush(_titleBarForeColor);
24     g.DrawString(Text,
25         SystemFonts.CaptionFont,
26         brsText,
27         new RectangleF(txtX,
28             TitleBarRectangle.Top + (TitleBarRectangle.Bottom - szText.Height) / 2,
29             Width - BorderWidth * 2,
30             TitleBarHeight),
31         StringFormat.GenericDefault);
32 
33     g.Dispose();
34     ReleaseDC(Handle, hdc);
35 }

随后绘制标题栏按钮，犹豫篇幅限制，在此不多赘述，详见源码中CreateButtonImages()与DrawTitleButtons()。

至此，表面工作基本做完了，但这个窗口还不像个窗口，因为最小化、最大化、关闭以及调整窗口大小都不好用。

为什么？因为还有很多工作要做，首先，同样在WndProc中处理WM_NCHITTEST消息，通过m.Result指定当前鼠标位置位于标题栏、最小化按钮、最大化按钮、关闭按钮或上下左右边框

 1 case WM_NCHITTEST:
 2     {
 3         base.WndProc(ref m);
 4 
 5         Point pt = PointToClient(new Point((int)m.LParam & 0xFFFF, (int)m.LParam >> 16 & 0xFFFF));
 6 
 7         _userSizedOrMoved = true;
 8 
 9         switch (_formBorderStyle)
10         {
11             case FormBorderStyle.None:
12                 break;
13             case FormBorderStyle.FixedSingle:
14             case FormBorderStyle.Fixed3D:
15             case FormBorderStyle.FixedDialog:
16             case FormBorderStyle.FixedToolWindow:
17                 if (pt.Y < 0)
18                 {
19                     _userSizedOrMoved = false;
20                     m.Result = (IntPtr)HTCAPTION;
21                 }
22 
23                 if (CorrectToLogical(CloseButtonRectangle).Contains(pt))
24                     m.Result = (IntPtr)HTCLOSE;
25                 if (CorrectToLogical(MaximizeButtonRectangle).Contains(pt))
26                     m.Result = (IntPtr)HTMAXBUTTON;
27                 if (CorrectToLogical(MinimizeButtonRectangle).Contains(pt))
28                     m.Result = (IntPtr)HTMINBUTTON;
29 
30                 break;
31             case FormBorderStyle.Sizable:
32             case FormBorderStyle.SizableToolWindow:
33                 if (pt.Y < 0)
34                 {
35                     _userSizedOrMoved = false;
36                     m.Result = (IntPtr)HTCAPTION;
37                 }
38 
39                 if (CorrectToLogical(CloseButtonRectangle).Contains(pt))
40                     m.Result = (IntPtr)HTCLOSE;
41                 if (CorrectToLogical(MaximizeButtonRectangle).Contains(pt))
42                     m.Result = (IntPtr)HTMAXBUTTON;
43                 if (CorrectToLogical(MinimizeButtonRectangle).Contains(pt))
44                     m.Result = (IntPtr)HTMINBUTTON;
45 
46                 if (WindowState == FormWindowState.Maximized)
47                     break;
48 
49                 bool bTop = pt.Y <= -TitleBarHeight + BorderWidth;
50                 bool bBottom = pt.Y >= Height - TitleBarHeight - BorderWidth;
51                 bool bLeft = pt.X <= BorderWidth;
52                 bool bRight = pt.X >= Width - BorderWidth;
53 
54                 if (bLeft)
55                 {
56                     _userSizedOrMoved = true;
57                     if (bTop)
58                         m.Result = (IntPtr)HTTOPLEFT;
59                     else if (bBottom)
60                         m.Result = (IntPtr)HTBOTTOMLEFT;
61                     else
62                         m.Result = (IntPtr)HTLEFT;
63                 }
64                 else if (bRight)
65                 {
66                     _userSizedOrMoved = true;
67                     if (bTop)
68                         m.Result = (IntPtr)HTTOPRIGHT;
69                     else if (bBottom)
70                         m.Result = (IntPtr)HTBOTTOMRIGHT;
71                     else
72                         m.Result = (IntPtr)HTRIGHT;
73                 }
74                 else if (bTop)
75                 {
76                     _userSizedOrMoved = true;
77                     m.Result = (IntPtr)HTTOP;
78                 }
79                 else if (bBottom)
80                 {
81                     _userSizedOrMoved = true;
82                     m.Result = (IntPtr)HTBOTTOM;
83                 }
84                 break;
85             default:
86                 throw new ArgumentOutOfRangeException();
87         }
88         break;
89     }

随后以同样的方式处理WM_NCLBUTTONDBLCLK、WM_NCLBUTTONDOWN、WM_NCLBUTTONUP、WM_NCMOUSEMOVE等消息，进行标题栏按钮等元素重绘，不多赘述。

现在窗口进行正常的单击、双击、调整尺寸，我们在最后为窗口添加阴影

首先定义一个可以承载32位位图的分层窗口(Layered Window)来负责主窗口阴影的呈现，详见源码中XFormShadow类，此处仅列出用于创建分层窗口的核心代码：

 1 private void UpdateBmp(Bitmap bmp)
 2 {
 3     if (!IsHandleCreated) return;
 4 
 5     if (!Image.IsCanonicalPixelFormat(bmp.PixelFormat) || !Image.IsAlphaPixelFormat(bmp.PixelFormat))
 6         throw new ArgumentException(@"位图格式不正确", nameof(bmp));
 7 
 8     IntPtr oldBits = IntPtr.Zero;
 9     IntPtr screenDC = GetDC(IntPtr.Zero);
10     IntPtr hBmp = IntPtr.Zero;
11     IntPtr memDc = CreateCompatibleDC(screenDC);
12 
13     try
14     {
15         POINT formLocation = new POINT(Left, Top);
16         SIZE bitmapSize = new SIZE(bmp.Width, bmp.Height);
17         BLENDFUNCTION blendFunc = new BLENDFUNCTION(
18             AC_SRC_OVER,
19             0,
20             255,
21             AC_SRC_ALPHA);
22 
23         POINT srcLoc = new POINT(0, 0);
24 
25         hBmp = bmp.GetHbitmap(Color.FromArgb(0));
26         oldBits = SelectObject(memDc, hBmp);
27 
28         UpdateLayeredWindow(
29             Handle,
30             screenDC,
31             ref formLocation,
32             ref bitmapSize,
33             memDc,
34             ref srcLoc,
35             0,
36             ref blendFunc,
37             ULW_ALPHA);
38     }
39     finally
40     {
41         if (hBmp != IntPtr.Zero)
42         {
43             SelectObject(memDc, oldBits);
44             DeleteObject(hBmp);
45         }
46 
47         ReleaseDC(IntPtr.Zero, screenDC);
48         DeleteDC(memDc);
49     }
50 }

最后通过路径渐变画刷创建阴影位图，通过位图构建分层窗口，并与主窗口建立父子关系：

 1 /// <summary>
 2 /// 构建阴影
 3 /// </summary>
 4 private void BuildShadow()
 5 {
 6     lock (this)
 7     {
 8         _buildingShadow = true;
 9 
10         if (_shadow != null && !_shadow.IsDisposed && !_shadow.Disposing)
11         {
12             // 解除父子窗口关系
13             SetWindowLong(
14                 Handle,
15                 GWL_HWNDPARENT,
16                 0);
17 
18             _shadow.Dispose();
19         }
20 
21         Bitmap bmpBackground = new Bitmap(Width + BorderWidth * 4, Height + BorderWidth * 4);
22 
23         GraphicsPath gp = new GraphicsPath();
24         gp.AddRectangle(new Rectangle(0, 0, bmpBackground.Width, bmpBackground.Height));
25 
26         using (Graphics g = Graphics.FromImage(bmpBackground))
27         using (PathGradientBrush brs = new PathGradientBrush(gp))
28         {
29             g.CompositingMode = CompositingMode.SourceCopy;
30             g.InterpolationMode = InterpolationMode.HighQualityBicubic;
31             g.PixelOffsetMode = PixelOffsetMode.HighQuality;
32             g.SmoothingMode = SmoothingMode.AntiAlias;
33 
34             // 中心颜色
35             brs.CenterColor = Color.FromArgb(100, Color.Black);
36             // 指定从实际阴影边界到窗口边框边界的渐变
37             brs.FocusScales = new PointF(1 - BorderWidth * 4F / Width, 1 - BorderWidth * 4F / Height);
38             // 边框环绕颜色
39             brs.SurroundColors = new[] { Color.FromArgb(0, 0, 0, 0) };
40             // 掏空窗口实际区域
41             gp.AddRectangle(new Rectangle(BorderWidth * 2, BorderWidth * 2, Width, Height));
42             g.FillPath(brs, gp);
43         }
44 
45         gp.Dispose();
46 
47         _shadow = new XFormShadow(bmpBackground);
48 
49         _buildingShadow = false;
50 
51         AlignShadow();
52         _shadow.Show();
53 
54         // 设置父子窗口关系
55         SetWindowLong(
56             Handle,
57             GWL_HWNDPARENT,
58             _shadow.Handle.ToInt32());
59 
60         Activate();
61     }//end of lock(this)
62 }

感谢大家能读到这里，代码中如有错误，或存在其它建议，欢迎在评论区或Github指正。

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