CodeProject - Where's the ImageCombo control?（重用已有控件，定制自己的控件的一个例子）

作者：Niels Penneman   翻译：小新0574

原文链接：http://www.codeproject.com/cs/combobox/ImageCombo_NET.asp

Introduction

When I started programming in .NET, I wondered where the ImageCombo control had gone (I used to program in VB6). The .NET Framework didn't seem to have this functionality built-in, but it's very easy to add it.

当我开始使用.NET编程后，我感到很惊讶，ImageCombo 控件去哪了呢？（我以前使用VB6编程）.NET框架似乎没有内建这个功能，不过要构造它很简单。

Using the code

The code consists of two classes: ImageCombo and ImageComboItem. If you want to use them in C#, just copy them into your project; for other .NET languages, you can add a reference to the library.

代码由两个类组成：ImageCombo 和 ImageComboItem。如果你想在你的C#代码里使用它们，只要把它们复制到你的工程里就行了；对于其他.NET语言，你只要增加一个对这个类库的引用就行了。（译注：把这两个类编译成dll，在工程里引用就行了）

The control inherits from ComboBox and introduces one new member: the ImageList property, which doesn't require any further explanation. The control is owner drawn and there is a custom drawing method defined, so don't change its DrawMode property if you want to see the images.

这个控件继承自ComboBox ，增加了一个新的成员：ImageList 属性，这不需要多做解释了吧。这个控件是自绘的，控件定义一个自定义的绘制方法，所以如果你想看到图像，就不要改变它的DrawMode属性。

The ImageComboItem class inherits from Object. You can set a customForeColor and it has a Mark property which determines if the item is shown in bold font style (does not work if owner font is already bold).

ImageComboItem类继承自Object。你可以设置一个自己的ForeColor ，这个类有一个Mark属性，这个属性决定是否项使用粗体显示。（如果项已经是粗体了，这个属性就不会起作用）。

To add an item to an ImageCombo with text "Icon 0" and image index 0, use the following code:

要增加一个使用文本“Icon 0”和（ImageList里）索引值为0的图像的ImageCombo （项）。使用一下代码：

imageCombo.Items.Add(new ImageComboItem("Icon 0", 0));

Code listing: ImageCombo class

using System;
using System.Drawing;

namespace System.Windows.Forms
{

    public class ImageCombo : ComboBox
    {
        private ImageList imgs = new ImageList();

        // constructor
        public ImageCombo()
        {
            // set draw mode to owner draw
            this.DrawMode = DrawMode.OwnerDrawFixed;    
        }

        // ImageList property
        public ImageList ImageList 
        {
            get 
            {
                return imgs;
            }
            set 
            {
                imgs = value;
            }
        }

        // customized drawing process
        protected override void OnDrawItem(DrawItemEventArgs e)
        {
            // draw background & focus rect
            e.DrawBackground();
            e.DrawFocusRectangle();

            // check if it is an item from the Items collection
            if (e.Index < 0)

                // not an item, draw the text (indented)
                e.Graphics.DrawString(this.Text, e.Font, 
                        new SolidBrush(e.ForeColor), e.Bounds.Left + 
                        imgs.ImageSize.Width, e.Bounds.Top);

            else
            {
                
                // check if item is an ImageComboItem
                if (this.Items[e.Index].GetType() == typeof(ImageComboItem)) 
                {                                                            

                    // get item to draw
                    ImageComboItem item = (ImageComboItem) 
                        this.Items[e.Index];

                    // get forecolor & font
                    Color forecolor = (item.ForeColor != 
                         Color.FromKnownColor(KnownColor.Transparent)) ? 
                         item.ForeColor : e.ForeColor;
                    Font font = item.Mark ? new Font(e.Font, 
                         FontStyle.Bold) : e.Font;

                    // -1: no image
                    if (item.ImageIndex != -1) 
                    {
                        // draw image, then draw text next to it
                        this.ImageList.Draw(e.Graphics, 
                           e.Bounds.Left, e.Bounds.Top, item.ImageIndex);
                        e.Graphics.DrawString(item.Text, font, 
                           new SolidBrush(forecolor), e.Bounds.Left + 
                           imgs.ImageSize.Width, e.Bounds.Top);
                    }
                    else
                        // draw text (indented)
                        e.Graphics.DrawString(item.Text, font, 
                            new SolidBrush(forecolor), e.Bounds.Left + 
                            imgs.ImageSize.Width, e.Bounds.Top);

                }
                else
                
                    // it is not an ImageComboItem, draw it
                    e.Graphics.DrawString(this.Items[e.Index].ToString(), 
                      e.Font, new SolidBrush(e.ForeColor), e.Bounds.Left + 
                      imgs.ImageSize.Width, e.Bounds.Top);
                
            }

            base.OnDrawItem (e);
        }
        
    }

}

Code listing: ImageComboItem class

using System;
using System.Drawing;

namespace System.Windows.Forms
{

    public class ImageComboItem : object
    {
        // forecolor: transparent = inherit
        private Color forecolor = Color.FromKnownColor(
                KnownColor.Transparent);
        private bool mark = false;
        private int imageindex = -1;
        private object tag = null;
        private string text = null;        
        
        // constructors
        public ImageComboItem()
        {
        }

        public ImageComboItem(string Text) 
        {
            text = Text;    
        }

        public ImageComboItem(string Text, int ImageIndex)
        {
            text = Text;
            imageindex = ImageIndex;
        }

        public ImageComboItem(string Text, int ImageIndex, bool Mark)
        {
            text = Text;
            imageindex = ImageIndex;
            mark = Mark;
        }

        public ImageComboItem(string Text, int ImageIndex, 
            bool Mark, Color ForeColor)
        {
            text = Text;
            imageindex = ImageIndex;
            mark = Mark;
            forecolor = ForeColor;
        }

        public ImageComboItem(string Text, int ImageIndex, 
               bool Mark, Color ForeColor, object Tag)
        {
            text = Text;
            imageindex = ImageIndex;
            mark = Mark;
            forecolor = ForeColor;
            tag = Tag;
        }

        // forecolor
        public Color ForeColor 
        {
            get 
            {
                return forecolor;
            }
            set
            {
                forecolor = value;
            }
        }

        // image index
        public int ImageIndex 
        {
            get 
            {
                return imageindex;
            }
            set 
            {
                imageindex = value;
            }
        }

        // mark (bold)
        public bool Mark
        {
            get
            {
                return mark;
            }
            set
            {
                mark = value;
            }
        }

        // tag
        public object Tag
        {
            get
            {
                return tag;
            }
            set
            {
                tag = value;
            }
        }

        // item text
        public string Text 
        {
            get
            {
                return text;
            }
            set
            {
                text = value;
            }
        }
        
        // ToString() should return item text
        public override string ToString() 
        {
            return text;
        }

    }

}

About Niels Penneman

 

 I have learnt to program in VB3 when I was about 10. I also learnt Pascal, I moved on to VB5 and later VB6, tried some Visual J++ (1.1) and I have little knowledge of ANSI C. Nowadays I mostly use VB.NET and C# .NET.

     

 我在大概10岁的时候使用VB3开始学习编程。我也学了Pascal，转移到VB5，然后VB6，尝试了一些Visual J++ (1.1)，我几乎不怎么了解ANSI C。现在我主要使用VB.NET和C#.NET。

 

I am currently studying science and maths in the last year of secondary education (maybe a weird way to explain it but it's because I don't know how YOUR educational system is organized ).

 

我现在在学习初中（secondary education）最后一年的自然科学与数学的课程（也许这样解释显得有些奇怪，但是是因为我不知道你们的教育体系是怎样组织的）。