C# C# WinForm控件美化扩展系列之ImageComboBox

前面介绍了两篇关于ComboBox扩展和美化的文章：C# WinForm控件美化扩展系列之ComboBox组合框控件和C# WinForm控件美化扩展系列之给ComboBox加水印，今天将在前两篇的基础上实现一个ImageComboBox控件，ImageComboBox控件拥有以下功能：

(1)  美化下拉按钮和边框，前面的文章已经实现。

(2)  当ComboBox没有控件选择项和没有焦点时显示提示用户操作信息，前面的也文章已经实现。

(3)  在下拉列表框的项中显示图标，项可以缩进。

(4)  在ComboBox控件中也显示图标。

来看看最终需要实现的效果：

 

图1 ImageComboBox DropDownList效果
 

 

图2 ImageComboBox DropDown效果
 

这篇文章中我们重点需要实现的是(3)、(4)两项功能，下面我们来介绍具体实现的方法。

第一步,实现ImageComboBoxItem类。

要实现显示图标，当然要给每个项添加与图标相关的信息了，ImageComboBoxItem类应该包括以下内容：文本(Text)、缩进的级别(Level)、图标的索引(ImageIndex、ImageKey)，用户数据(Tag)。ImageComboBoxItem类实现了ISerializable接口，实现自定义序列化。ImageComboBoxItem类的类视图如下：

 

图3 ImageComboxItem类视图

 

ImageComboBoxItem类的代码如下： 

    [Serializable]

    [DefaultProperty("Text")]

    [TypeConverter(

        typeof(ExpandableObjectConverter))]

    public class ImageComboBoxItem : 

        IDisposable, ISerializable

    ...{

        Fields#region Fields



        private ImageComboBox _imageComboBox;

        private string _text = "ImageComboBoxItem";

        private ImageComboBoxItemImageIndexer _imageIndexer;

        private object _tag;

        private int _level;



        #endregion



        Constructors#region Constructors



        public ImageComboBoxItem()

        ...{

        }



        public ImageComboBoxItem(string text)

            : this(text, -1, 0)

        ...{

        }



        public ImageComboBoxItem(

            string text, int imageIndex)

            : this(text, imageIndex, 0)

        ...{

        }



        public ImageComboBoxItem(

            string text, string imageKey)

            : this(text, imageKey, 0)

        ...{

        }



        public ImageComboBoxItem(

            string text, int imageIndex, int level)

            : this()

        ...{

            _text = text;

            ImageIndexer.Index = imageIndex;

            _level = level;

        }



        public ImageComboBoxItem(

           string text, string imageKey, int level)

            : this()

        ...{

            _text = text;

            ImageIndexer.Key = imageKey;

            _level = level;

        }



        protected ImageComboBoxItem(

            SerializationInfo info,

            StreamingContext context)

            : this()

        ...{

            Deserialize(info, context);

        }



        #endregion



        Properties#region Properties



        [Localizable(true)]

        public string Text

        ...{

            get 

            ...{

                if (_text != null)

                ...{

                    return _text;

                }

                return "";

            }

            set

            ...{

                _text = value; 

            }

        }



        [Bindable(true)]

        [Localizable(false)]

        [DefaultValue("")]

        [TypeConverter(typeof(StringConverter))]

        [DesignerSerializationVisibility(

            DesignerSerializationVisibility.Hidden)]

        public object Tag

        ...{

            get ...{ return _tag; }

            set ...{ _tag = value; }

        }



        [DefaultValue(0)]

        [Localizable(true)]

        [RefreshProperties(RefreshProperties.Repaint)]

        [DesignerSerializationVisibility(

           DesignerSerializationVisibility.Hidden)]

        public int Level

        ...{

            get ...{ return _level; }

            set 

            ...{

                if (_level < 0)

                ...{

                    throw new ArgumentOutOfRangeException("level");

                }

                _level = value; 

            }

        }



        [DefaultValue(-1)]

        [Localizable(true)]

        [RelatedImageList("ImageComboBox.ImageList")]

        [Editor(

            EditorAssemblyName.ImageIndexEditor,

            typeof(UITypeEditor))]

        [RefreshProperties(RefreshProperties.Repaint)]

        [DesignerSerializationVisibility(

            DesignerSerializationVisibility.Hidden)]

        [TypeConverter(typeof(NoneExcludedImageIndexConverter))]

        public int ImageIndex

        ...{

            get

            ...{

                if (((ImageIndexer.Index != -1) && 

                    (ImageList != null)) && 

                    (ImageIndexer.Index >= ImageList.Images.Count))

                ...{

                    return ImageList.Images.Count - 1;

                }

                return ImageIndexer.Index;

            }

            set

            ...{

                if (value < -1)

                ...{

                    throw new ArgumentOutOfRangeException("ImageIndex");

                }

                ImageIndexer.Index = value;

            }

        }



        [DefaultValue("")]

        [Localizable(true)]

        [RelatedImageList("ImageComboBox.ImageList")]

        [RefreshProperties(RefreshProperties.Repaint)]

        [Editor(

            EditorAssemblyName.ImageIndexEditor, 

            typeof(UITypeEditor))]

        [DesignerSerializationVisibility(

            DesignerSerializationVisibility.Hidden)]

        [TypeConverter(typeof(ImageKeyConverter))]

        public string ImageKey

        ...{

            get

            ...{

                return ImageIndexer.Key;

            }

            set

            ...{

                ImageIndexer.Key = value;

            }

        }



        [Browsable(false)]

        public ImageComboBox ImageComboBox

        ...{

            get ...{ return _imageComboBox; }

        }



        internal Image Image

        ...{

            get

            ...{

                int actualIndex = ImageIndexer.ActualIndex;

                if (ImageList != null &&

                    ImageList.Images.Count > 0 &&

                    actualIndex != -1)

                ...{

                    return ImageList.Images[actualIndex];

                }

                return null;

            }

        }



        [Browsable(false)]

        internal ImageList ImageList

        ...{

            get

            ...{

                if (ImageComboBox != null)

                ...{

                    return ImageComboBox.ImageList;

                }

                return null;

            }

        }



        internal ImageComboBoxItemImageIndexer ImageIndexer

        ...{

            get

            ...{

                if (_imageIndexer == null)

                ...{

                    _imageIndexer = 

                        new ImageComboBoxItemImageIndexer(this);

                }

                return _imageIndexer;

            }

        }



        #endregion



        Methods#region Methods



        public override string ToString()

        ...{

            return _text;

        }



        internal void Host(ImageComboBox parent)

        ...{

            _imageComboBox = parent;

        }



        [SecurityPermission(

            SecurityAction.Demand, 

            Flags = SecurityPermissionFlag.SerializationFormatter), 

        SecurityPermission(

            SecurityAction.InheritanceDemand, 

            Flags = SecurityPermissionFlag.SerializationFormatter)]

        protected virtual void Serialize(

            SerializationInfo info, StreamingContext context)

        ...{

            info.AddValue("Text", Text);

            info.AddValue("Level", Level);

            info.AddValue("ImageIndex", ImageIndexer.Index);

            if (!string.IsNullOrEmpty(ImageIndexer.Key))

            ...{

                info.AddValue("ImageKey", ImageIndexer.Key);

            }

        }



        protected virtual void Deserialize(

            SerializationInfo info,

            StreamingContext context)

        ...{

            string imageKey = null;

            int imageIndex = -1;

            SerializationInfoEnumerator enumerator = info.GetEnumerator();

            while (enumerator.MoveNext())

            ...{

                SerializationEntry current = enumerator.Current;

                if (current.Name == "Text")

                ...{

                    Text = info.GetString(current.Name);

                }

                else if (current.Name == "Level")

                ...{

                    Level = info.GetInt32(current.Name);

                }

                else

                ...{

                    if (current.Name == "ImageIndex")

                    ...{

                        imageIndex = info.GetInt32(current.Name);

                        continue;

                    }

                    if (current.Name == "ImageKey")

                    ...{

                        imageKey = info.GetString(current.Name);

                        continue;

                    }

                }

            }

            if (imageKey != null)

            ...{

                ImageKey = imageKey;

            }

            else if (imageIndex != -1)

            ...{

                ImageIndex = imageIndex;

            }

        }



        #endregion



        ISerializable 成员#region ISerializable 成员



        [SecurityPermission(

            SecurityAction.LinkDemand,

            Flags = SecurityPermissionFlag.SerializationFormatter)]

        void ISerializable.GetObjectData(

            SerializationInfo info, StreamingContext context)

        ...{

            Serialize(info, context);

        }



        #endregion



        IDisposable 成员#region IDisposable 成员



        public void Dispose()

        ...{

            _imageComboBox = null;

            _imageIndexer = null;

            _tag = null;

        }



        #endregion



        ImageComboBoxItemImageIndexer Class

        #region ImageComboBoxItemImageIndexer Class

        internal class ImageComboBoxItemImageIndexer

            : ImageIndexer

        ...{

            private ImageComboBoxItem _owner;



            public ImageComboBoxItemImageIndexer(

                ImageComboBoxItem owner)

            ...{

                _owner = owner;

            }



            public override ImageList ImageList

            ...{

                get

                ...{

                    if (_owner != null)

                    ...{

                        return _owner.ImageList;

                    }

                    return null;

                }

                set

                ...{

                }

            }

        }



        #endregion

    }

第二步，实现ImageComboBoxItemCollection类。

ImageComboBoxItemCollection类实现跟ComboBox.ObjectCollection类一样的功能，用来代替ComboBox控件中ComboBox.ObjectCollection类，定义一个新的Items来存储ImageComboBoxItem对象，来实现ImageComboBox控件设计时可以支持ImageComboBoxItem对象的设计。

第三步，给ImageComboBox控件添加一些属性。

ImageComboBox控件主要需要添加几个属性：图标集合(ImageList)、没有选择项时ComboBox中显示的默认图标(DefaultImage)、缩进值(Indent)、提示信息(EmptyTextTip)、提示信息的文本颜色(EmptyTextTipColor)。还需要覆盖一些属性，这里不一一列出了，看下面的ImageComboBox控件的类视图：

 

图4 ImageComboBox类视图

第四步，实现EditorNativeWimdow类。

EditorNativeWimdow类的主要功能是实现当ImageComboBox控件的列表模式设为非DropDownList的时候，即DropDownStyle不是ComboBoxStyle.DropDownList的时候，实现在Editor中绘制图标。EditorNativeWimdow类的代码如下： 

private class EditorNativeWimdow 

    : NativeWindow, IDisposable

...{

    Fields#region Fields



    private ImageComboBox _owner;



    private const int EC_LEFTMARGIN = 0x1;

    private const int EC_RIGHTMARGIN = 0x2;

    private const int EC_USEFONTINFO = 0xFFFF;

    private const int EM_SETMARGINS = 0xD3;

    private const int EM_GETMARGINS = 0xD4;



    #endregion



    Constructors#region Constructors



    public EditorNativeWimdow(

        ImageComboBox owner)

        : base()

    ...{

        _owner = owner;

        Attach();

    }



    #endregion



    Private Methods#region Private Methods



    private void Attach()

    ...{

        if (!Handle.Equals(IntPtr.Zero))

        ...{

            ReleaseHandle();

        }

        AssignHandle(_owner.EditHandle);

        SetMargin();

    }



    protected override void WndProc(

        ref Message m)

    ...{

        base.WndProc(ref m);



        switch (m.Msg)

        ...{

            case (int)NativeMethods.WindowsMessage.WM_SETFONT:

                SetMargin();

                break;

            case (int)NativeMethods.WindowsMessage.WM_PAINT:

                RePaint();

                break;

            case (int)NativeMethods.WindowsMessage.WM_SETFOCUS:

            case (int)NativeMethods.WindowsMessage.WM_KILLFOCUS:

                RePaint();

                break;

            case (int)NativeMethods.WindowsMessage.WM_LBUTTONDOWN:

            case (int)NativeMethods.WindowsMessage.WM_RBUTTONDOWN:

            case (int)NativeMethods.WindowsMessage.WM_MBUTTONDOWN:

                RePaint();

                break;

            case (int)NativeMethods.WindowsMessage.WM_LBUTTONUP:

            case (int)NativeMethods.WindowsMessage.WM_RBUTTONUP:

            case (int)NativeMethods.WindowsMessage.WM_MBUTTONUP:

                RePaint();

                break;

            case (int)NativeMethods.WindowsMessage.WM_LBUTTONDBLCLK:

            case (int)NativeMethods.WindowsMessage.WM_RBUTTONDBLCLK:

            case (int)NativeMethods.WindowsMessage.WM_MBUTTONDBLCLK:

                RePaint();

                break;

            case (int)NativeMethods.WindowsMessage.WM_KEYDOWN:

            case (int)NativeMethods.WindowsMessage.WM_CHAR:

            case (int)NativeMethods.WindowsMessage.WM_KEYUP:

                RePaint();

                break;

            case (int)NativeMethods.WindowsMessage.WM_MOUSEMOVE:

                if (!m.WParam.Equals(IntPtr.Zero))

                ...{

                    RePaint();

                }

                break;

        }

    }



    internal void SetMargin()

    ...{

        NearMargin(Handle, _owner.ItemHeight + 5);

    }



    private static bool IsRightToLeft(

        IntPtr handle)

    ...{

        int style = NativeMethods.GetWindowLong(

            handle, (int)NativeMethods.GWL.GWL_EXSTYLE);

        return (

            ((style & (int)NativeMethods.WS_EX.WS_EX_RIGHT)

            == (int)NativeMethods.WS_EX.WS_EX_RIGHT) ||

            ((style & (int)NativeMethods.WS_EX.WS_EX_RTLREADING)

            == (int)NativeMethods.WS_EX.WS_EX_RTLREADING) ||

            ((style & (int)NativeMethods.WS_EX.WS_EX_LEFTSCROLLBAR)

            == (int)NativeMethods.WS_EX.WS_EX_LEFTSCROLLBAR));

    }



    private static void FarMargin(

        IntPtr handle, int margin)

    ...{

        int message = IsRightToLeft(handle) ? 

        EC_LEFTMARGIN : EC_RIGHTMARGIN;

        if (message == EC_LEFTMARGIN)

        ...{

            margin = margin & 0xFFFF;

        }

        else

        ...{

            margin = margin * 0x10000;

        }

        NativeMethods.SendMessage(

            handle, 

            EM_SETMARGINS, 

            message, 

            margin);

    }



    internal static void NearMargin(

        IntPtr handle, int margin)

    ...{

        int message = IsRightToLeft(handle) ?

        EC_RIGHTMARGIN : EC_LEFTMARGIN;

        if (message == EC_LEFTMARGIN)

        ...{

            margin = margin & 0xFFFF;

        }

        else

        ...{

            margin = margin * 0x10000;

        }

        NativeMethods.SendMessage(

            handle, 

            EM_SETMARGINS, 

            message, 

            margin);

    }



    private void RePaint()

    ...{

        ImageComboBoxItem item = _owner.SelectedItem;



        NativeMethods.RECT rcClient = new NativeMethods.RECT();

        NativeMethods.GetClientRect(Handle, ref rcClient);

        bool rightToLeft = IsRightToLeft(Handle);



        IntPtr handle = Handle;

        IntPtr hdc = NativeMethods.GetDC(handle);

        if (hdc == IntPtr.Zero)

        ...{

            return;

        }

        try

        ...{

            using (Graphics g = Graphics.FromHdc(hdc))

            ...{

                int itemSize = _owner.ItemHeight;

                Rectangle imageRect = new Rectangle(

                    0, 

                    rcClient.Top + (rcClient.Bottom - itemSize) / 2,

                    itemSize, 

                    itemSize);

                Rectangle textRect = new Rectangle(

                    0, 

                    0,

                    rcClient.Right - itemSize - 6, 

                    rcClient.Bottom);



                if (rightToLeft)

                ...{

                    imageRect.X = rcClient.Right - itemSize - 2;

                    textRect.X = 2;

                }

                else

                ...{

                    imageRect.X = 2;

                    textRect.X = imageRect.Right + 2;

                }



                if (_owner.Text.Length == 0)

                ...{

                    DrawImage(

                       g,

                       imageRect,

                       _owner.DefaultImage,

                       _owner.DefaultImageList,

                       0,

                       _owner.Focused);



                    if (_owner.Text.Length == 0 &&

                        !string.IsNullOrEmpty(_owner.EmptyTextTip) &&

                        !_owner.Focused)

                    ...{

                        TextFormatFlags format =

                        TextFormatFlags.EndEllipsis |

                        TextFormatFlags.VerticalCenter;



                        if (_owner.RightToLeft == RightToLeft.Yes)

                        ...{

                            format |= 

                                (TextFormatFlags.RightToLeft | 

                                TextFormatFlags.Right);

                        }



                        TextRenderer.DrawText(

                            g,

                            _owner.EmptyTextTip,

                            _owner.Font,

                            textRect,

                            _owner.EmptyTextTipColor,

                            format);

                    }

                    return;

                }



                if (_owner.Text.Length > 0)

                ...{

                    using (SolidBrush brush =

                        new SolidBrush(_owner.BackColor))

                    ...{

                        g.FillRectangle(brush, imageRect);

                    }

                }



                if (_owner.Items.Count == 0)

                ...{

                    DrawImage(

                       g,

                       imageRect,

                       _owner.DefaultImage,

                       _owner.DefaultImageList,

                       0,

                       _owner.Focused);

                    return;

                }



                if (item == null)

                ...{

                    return;

                }



                DrawImage(

                    g,

                    imageRect,

                    item.Image,

                    _owner.ImageList,

                    item.ImageIndexer.ActualIndex,

                    _owner.Focused);

            }

        }

        finally

        ...{

            NativeMethods.ReleaseDC(handle, hdc);

        }

    }



    private void DrawImage(

        Graphics g,

        Rectangle imageRect,

        Image image,

        ImageList imageList,

        int imageIndex,

        bool focus)

    ...{

        using (SolidBrush brush = 

            new SolidBrush(_owner.BackColor))

        ...{

            g.FillRectangle(brush, imageRect);

        }



        if (image == null)

        ...{

            return;

        }



        using (InterpolationModeGraphics graphics =

               new InterpolationModeGraphics(

               g, InterpolationMode.HighQualityBicubic))

        ...{

            if (focus)

            ...{

                IntPtr hIcon = NativeMethods.ImageList_GetIcon(

                   imageList.Handle,

                   imageIndex,

                   (int)NativeMethods.ImageListDrawFlags.ILD_SELECTED);

                g.DrawIcon(Icon.FromHandle(hIcon), imageRect);

                NativeMethods.DestroyIcon(hIcon);

            }

            else

            ...{

                g.DrawImage(

                    image,

                    imageRect,

                    0,

                    0,

                    image.Width,

                    image.Height,

                    GraphicsUnit.Pixel);

            }

        }

    }



    #endregion



    IDisposable 成员#region IDisposable 成员



    public void Dispose()

    ...{

        _owner = null;

        base.ReleaseHandle();

    }



    #endregion

}

第五步，重写OnCreateControl、OnHandleDestroyed方法。

重写这两个方法主要是为了ImageComboBox控件的DropDownStyle为不同的值时，控制是否需要在Editor中绘制图标，这两个方法的代码如下： 

protected override void OnCreateControl()

...{

    base.OnCreateControl();

    if (DropDownStyle != ComboBoxStyle.DropDownList &&

        !DesignMode)

    ...{

        if (_nativeWimdow == null)

        ...{

            _nativeWimdow = new EditorNativeWimdow(this);

        }

    }

}



protected override void OnHandleDestroyed(EventArgs e)

...{

    if (_nativeWimdow != null)

    ...{

        _nativeWimdow.Dispose();

        _nativeWimdow = null;

    }

    base.OnHandleDestroyed(e);

}

第六步，重写OnDropDown方法。

重写这个方法是为了实现调节下拉列表框显示的大小，因为画了图标，以免项显示不完全。OnDropDown方法代码如下： 

protected override void OnDropDown(

   EventArgs e)

...{

    base.OnDropDown(e);



    int ddWidth = 0;

    int textWidth = 0;

    int itemWidth = 0;

    int scrollBarWidth =

        Items.Count > MaxDropDownItems ?

           SystemInformation.VerticalScrollBarWidth :

           0;

    Graphics g = CreateGraphics();



    foreach (ImageComboBoxItem item in Items)

    ...{

        textWidth = g.MeasureString(

            item.Text, Font).ToSize().Width;

        itemWidth =

            textWidth +

            ItemHeight + 8 +

            _indent * item.Level +

            scrollBarWidth;



        if (itemWidth > ddWidth)

            ddWidth = itemWidth;

    }



    DropDownWidth = (ddWidth > Width) ?

        ddWidth : Width;

    g.Dispose();

}
 

第七步，重绘列表项，让其缩进和显示图标。

重绘列表项，需要把ImageComboBox控件的DrawMode设为DrawMode.OwnerDrawFixed，然后通过重写OnDrawItem方法实现，具体代码如下： 

protected override void OnDrawItem(DrawItemEventArgs e)

...{

    if (e.Index != -1)

    ...{

        ImageComboBoxItem item = Items[e.Index];

        Graphics g = e.Graphics;

        Rectangle bounds = e.Bounds;



        int indentOffset = Indent * item.Level;



        if ((e.State & DrawItemState.ComboBoxEdit) ==

            DrawItemState.ComboBoxEdit)

        ...{

            indentOffset = 0;

        }



        int imageWidth = bounds.Height;

        Rectangle imageRect;

        Rectangle textRect;

        TextFormatFlags format =

            TextFormatFlags.VerticalCenter |

            TextFormatFlags.SingleLine |

            TextFormatFlags.WordBreak;



        imageRect = new Rectangle(

            bounds.Left + indentOffset + 2,

            bounds.Top,

            imageWidth,

            imageWidth);

        textRect = new Rectangle(

            imageRect.Right + 3,

            bounds.Y,

            bounds.Width - imageRect.Width - indentOffset - 5,

            bounds.Height);



        Rectangle backRect = new Rectangle(

           textRect.X,

           textRect.Y + 1,

           textRect.Width,

           textRect.Height - 2);



        backRect.Width = TextRenderer.MeasureText(

            item.Text, e.Font, textRect.Size, format).Width;



        if (base.RightToLeft == RightToLeft.Yes)

        ...{

            imageRect.X = bounds.Right - imageRect.Right;

            textRect.X = bounds.Right - textRect.Right;

            backRect.X = textRect.Right - backRect.Width;

        }



        bool selected = ((e.State & DrawItemState.Selected) ==

            DrawItemState.Selected);



        Color backColor = selected ?

            SystemColors.Highlight : base.BackColor;



        using (Brush backBrush = new SolidBrush(backColor))

        ...{

            g.FillRectangle(backBrush, backRect);

        }



        if (selected)

        ...{

            ControlPaint.DrawFocusRectangle(

                g,

                backRect);

        }



        Image image = item.Image;

        if (image != null)

        ...{

            using (InterpolationModeGraphics graphics =

                new InterpolationModeGraphics(

                g, InterpolationMode.HighQualityBicubic))

            ...{

                if (selected)

                ...{

                    IntPtr hIcon = NativeMethods.ImageList_GetIcon(

                       ImageList.Handle,

                       item.ImageIndexer.ActualIndex,

                       (int)NativeMethods.ImageListDrawFlags.ILD_SELECTED);

                    g.DrawIcon(Icon.FromHandle(hIcon), imageRect);

                    NativeMethods.DestroyIcon(hIcon);

                }

                else

                ...{

                    g.DrawImage(

                        image, 

                        imageRect,

                        0,

                        0,

                        image.Width,

                        image.Height,

                        GraphicsUnit.Pixel);

                }

            }

        }



        TextRenderer.DrawText(

            g,

            item.Text,

            e.Font,

            textRect,

            base.ForeColor,

            format);

    }

}

到此为止，ImageComboBox控件需要实现的功能就完成了。

转载：http://www.csharpwin.com/csharpresource/7620r2070.shtml