禁用组合框中的特定项目

Question

我有一个 WinForms 应用程序，我想知道是否有更优雅的方式来禁用 Combobox 项，而无需更改所有禁用值的 SelectedIndex 属性 -1。

我一直在谷歌搜索，很多解决方案都涉及 ASP.Net DropDownLists，但这个LINK 看起来很有希望。我想我可能必须构建自己的 ComboBox 控件，但在我重新发明轮子之前，我想我会在这里询问是否可能。

更新

感谢 Arif Eqbal，这是最终的解决方案：

//Add a Combobox to a form and name it comboBox1
//
    using System;
    using System.Drawing;
    using System.Windows.Forms;

    namespace WindowsFormsApplication6
    {
        public partial class Form1 : Form
        {
            public Form1()
            {
                InitializeComponent();
                this.comboBox1.DrawMode = DrawMode.OwnerDrawFixed;
                this.comboBox1.DrawItem += new System.Windows.Forms.DrawItemEventHandler(this.comboBox1_DrawItem);
                this.comboBox1.SelectedIndexChanged += new System.EventHandler(this.comboBox1_SelectedIndexChanged);
            }

            private void Form1_Load(object sender, EventArgs e)
            {
                this.comboBox1.Items.Add("Test1");
                this.comboBox1.Items.Add("Test2");
                this.comboBox1.Items.Add("Test3");
                this.comboBox1.Items.Add("Test4");
                this.comboBox1.Items.Add("Test5");
                this.comboBox1.Items.Add("Test6");
                this.comboBox1.Items.Add("Test7");
            }

            Font myFont = new Font("Aerial", 10, FontStyle.Underline|FontStyle.Regular);
            Font myFont2 = new Font("Aerial", 10, FontStyle.Italic|FontStyle.Strikeout);

            private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
            {
                if (e.Index == 1 || e.Index == 4 || e.Index == 5)//We are disabling item based on Index, you can have your logic here
                {
                    e.Graphics.DrawString(comboBox1.Items[e.Index].ToString(), myFont2, Brushes.LightSlateGray, e.Bounds);
                }
                else
                {
                    e.DrawBackground();
                    e.Graphics.DrawString(comboBox1.Items[e.Index].ToString(), myFont, Brushes.Black, e.Bounds);
                    e.DrawFocusRectangle();
                }
            }

            void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
            {
                if (comboBox1.SelectedIndex == 1 || comboBox1.SelectedIndex == 4 || comboBox1.SelectedIndex == 5)
                    comboBox1.SelectedIndex = -1;
            }
        }
    }

Answer 1

试试这个...它是否符合您的目的：

我假设您有一个名为 ComboBox1 的组合框，并且您想禁用第二个项目，即索引为 1 的项目。

将组合框的DrawMode属性设置为OwnerDrawFixed，然后如下处理这两个事件：

Font myFont = new Font("Aerial", 10, FontStyle.Regular);

private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
{        
    if (e.Index == 1) //We are disabling item based on Index, you can have your logic here
    {
        e.Graphics.DrawString(comboBox1.Items[e.Index].ToString(), myFont, Brushes.LightGray, e.Bounds);
    }
    else
    {
        e.DrawBackground();
        e.Graphics.DrawString(comboBox1.Items[e.Index].ToString(), myFont, Brushes.Black, e.Bounds);
        e.DrawFocusRectangle();
    }
} 

void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (comboBox1.SelectedIndex == 1)
        comboBox1.SelectedIndex = -1;
}

Answer 2

这是我 100% 基于 Arif Eqbal 的答案。 改进如下：

• 重用 ComboBox 中的 Font 而不是创建新的（这样，如果您在设计器中更改它，您就不必更新代码）
• 重用默认的SystemBrushes（因此它应该与您的主题相匹配；但如果您手动更改 ComboBox 中使用的颜色，它将不起作用）
• 对于禁用的项目，我必须重绘背景，否则每次重绘灰色项目时，它们的颜色会越来越接近黑色
• 创建专用的IsItemDisabled 方法以避免复制/粘贴

---

// Don't forget to change DrawMode, else the DrawItem event won't be called.
// this.comboBox1.DrawMode = System.Windows.Forms.DrawMode.OwnerDrawFixed;

private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
{
    ComboBox comboBox = (ComboBox)sender;

    if (IsItemDisabled(e.Index))
    {
        // NOTE we must draw the background or else each time we hover over the text it will be redrawn and its color will get darker and darker.
        e.Graphics.FillRectangle(SystemBrushes.Window, e.Bounds);
        e.Graphics.DrawString(comboBox.Items[e.Index].ToString(), comboBox.Font, SystemBrushes.GrayText, e.Bounds);
    }
    else
    {
        e.DrawBackground();

        // Using winwaed's advice for selected items:
        // Set the brush according to whether the item is selected or not
        Brush brush = ( (e.State & DrawItemState.Selected) > 0) ? SystemBrushes.HighlightText : SystemBrushes.ControlText;
        e.Graphics.DrawString(comboBox.Items[e.Index].ToString(), comboBox.Font, brush, e.Bounds);

        e.DrawFocusRectangle();
    }
}

void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    if (IsItemDisabled(comboBox1.SelectedIndex))
        comboBox1.SelectedIndex = -1;
}

bool IsItemDisabled(int index)
{
    // We are disabling item based on Index, you can have your logic here
    return index % 2 == 1;
}

Answer 3

这是进一步的修改。上述解决方案的问题是所选项目不可见，因为字体前景和背景选择都是黑暗的。所以字体要根据e.State的值来设置：

    private void comboBox1_DrawItem(object sender, DrawItemEventArgs e)
    {
        ComboBox comboBox = (ComboBox)sender;
        if (e.Index >= 0)
        {
            if (IsItemDisabled(e.Index))
            {
                e.Graphics.FillRectangle(SystemBrushes.Window, e.Bounds);
                e.Graphics.DrawString(comboBox.Items[e.Index].ToString(), comboBox.Font, Brushes.LightSlateGray, e.Bounds);
            }
            else
            {
                e.DrawBackground();

                // Set the brush according to whether the item is selected or not
                Brush br = ( (e.State & DrawItemState.Selected) > 0) ? SystemBrushes.HighlightText : SystemBrushes.ControlText;

                e.Graphics.DrawString(comboBox.Items[e.Index].ToString(), comboBox.Font, br, e.Bounds);
                e.DrawFocusRectangle();
            }
        }
    }