ListBox 更改特定项目的前景色

Question

我正在努力为列表框创建自定义功能。我需要我的 ListBox 来更改特定（“标记”）项目的前景色。不要与所选项目混淆。

所需功能：假设 ListBox 集合包含多个文件名。
当我双击一个项目时；该项目索引和对象存储在两个变量（索引和对象）中。
然后，这些变量将用于设置项目前景色（当未选择列表框项目时）。
Remaining Items 和 Item Rectangle 应使用默认属性绘制（在这种情况下，它们有自己的颜色属性以允许进一步定制）。

我的问题：

加载时不绘画
字符串是用“奇怪的字符”绘制的
选择项目时；我正在绘制“已标记”项目。

我真的很困惑。 MSDN 文档不是很清楚如何实现这一点；也不是 DrawItem 事件发生的方式和时间。

我一直在考虑几种选择；但是删除了所有内容并返回到当前代码以尝试理解逻辑和行为。

第一次尝试代码（原始问题代码）：

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Custom_Controls.Controls
{
    internal class MyPlaylist : ListBox
    {
        public MyPlaylist()
        {
            SetStyle(ControlStyles.OptimizedDoubleBuffer, true);

            // Enable ListBox Customized Design
            DrawMode = DrawMode.OwnerDrawVariable;
            //SelectionMode = SelectionMode.MultiExtended;
        }

        #region <Custom Properties>
        private int markedIndex = -1;
        public int MarkedIndex
        {
            get { return markedIndex; }
            set { markedIndex = value; Invalidate(); }
        }

        private object markedItem = string.Empty;
        public object MarkedItem
        {
            get { return markedItem; }
            set
            {
                markedItem = value;
                Invalidate();
            }
        }

        private Color markedItemForeColor = Color.Red;
        public Color MarkedItemForeColor
        {
            get { return markedItemForeColor; }
            set { markedItemForeColor = value; Invalidate(); }
        }


        private Color markedItemBackColor = Color.DimGray;
        public Color MarkedItemBackColor
        {
            get { return markedItemBackColor; }
            set { markedItemBackColor = value; Invalidate(); }
        }


        private Color selectionBackColor = Color.DeepSkyBlue;
        public Color SelectionBackColor
        {
            get { return selectionBackColor; }
            set { selectionBackColor = value; Invalidate(); }
        }


        private Color selectionForeColor = Color.White;
        public Color SelectionForeColor
        {
            get { return selectionForeColor; }
            set { selectionForeColor = value; Invalidate(); }
        }
        #endregion


        
    protected override void OnDrawItem(DrawItemEventArgs e) // When Selected?
    {
        e.DrawBackground();
        e.DrawFocusRectangle();

        //// Improve Graphic Quality and Pixel Precision
        e.Graphics.SmoothingMode = SmoothingMode.AntiAlias;
        e.Graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
        e.Graphics.PixelOffsetMode = PixelOffsetMode.HighQuality;

        
        using (var defaultForeBrush = new SolidBrush(Color.White))
        using (var markForeBrush = new SolidBrush(markedItemForeColor))
        {
            // Iterate over all the items
            for (int i = 0; i < Items.Count; i++)
            {
                var item = Items[i];

                // Draw "Marked" Item
                if (i == markedIndex)
                { 
                    e.Graphics.DrawString(Items[markedIndex].ToString(), e.Font, markForeBrush, e.Bounds, StringFormat.GenericDefault); 
                }

                // Draw Remaining Items
                else
                {
                    e.Graphics.DrawString(item.ToString(), e.Font, markForeBrush, e.Bounds, StringFormat.GenericDefault);
                }

                // Draw Selection Rectangle
                // ...
            }
        }
    }        



        #region <Overriden Events>
        protected override void OnPaint(PaintEventArgs e)
        {
            base.OnPaint(e);
        }

        protected override void OnDoubleClick(EventArgs e)
        {
            base.OnDoubleClick(e);

            SetMarkedItem();
        }

        protected override void OnMouseDoubleClick(MouseEventArgs e)
        {
            base.OnMouseDoubleClick(e);

            SetMarkedItem();
        }


        #region <Methods>
        private void SetMarkedItem()
        {
            markedIndex = SelectedIndex;
            markedItem = SelectedItem;
        } 
        #endregion
    }
}

我第二次尝试使用 Jimi 的帮助（当前代码）

变化：

我评论了 Pinvoke LB_ Enums 和 WndProc，因为我无法使其工作。
为了保持简单：我删除了三元运算符（但是我喜欢 Jimi 的代码用它们交替颜色的方式）。
SetMarker() 已还原为以前的版本。标记的项目从来没有那样绘制过。
自定义属性没有为画笔提供它们的价值；因此他们被暂时删除了。

当前问题： WndProc 确实需要重新实现以清除绘图（标记项）；并可能重绘控件，以便尽快更新标记。

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace Custom_Controls.Controls
{
    internal class MyPlaylist : ListBox
    {
        #region <Constructor>
        public MyPlaylist()
        {
            SetStyle(ControlStyles.OptimizedDoubleBuffer, true);

            DrawMode = DrawMode.OwnerDrawVariable;

            BackColor = Color.FromArgb(255, 25, 25, 25);
            ForeColor = Color.White;
            BorderStyle = BorderStyle.FixedSingle;
        }
        #endregion


        #region <Fields>
        //private const int LB_RESETCONTENT = 0x0184;
        //private const int LB_DELETESTRING = 0x0182;

        //TextFormatFlags flags = TextFormatFlags.PreserveGraphicsClipping | TextFormatFlags.LeftAndRightPadding | TextFormatFlags.VerticalCenter;
        #endregion


        #region <Custom Properties>
        // Tip: Always Verify that the new Values are Different from the Old Ones

        private int markedIndex = -1;
        public int MarkedIndex
        {
            get { return markedIndex; }
            set
            {
                if (value != markedIndex)
                {
                    markedIndex = value;
                    Invalidate();
                }
            }
        }

        // Read-only: just return the marked Item, set it using the Index only
        public object MarkedItem
        {
            get { return Items[markedIndex]; }
        }
        #endregion


        #region <Overriden Events>
        protected override void OnDrawItem(DrawItemEventArgs e)
        {
            if (Items.Count == 0) return;

            // Draw Selection:
            if (e.State.HasFlag(DrawItemState.Focus) || e.State.HasFlag(DrawItemState.Selected))
            {
                using (var brush = new SolidBrush(Color.FromArgb(255, 52, 52, 52)))
                {
                    // Background Rectangle
                    e.Graphics.FillRectangle(brush, e.Bounds);

                    // Item Text : Marked Item
                    if (e.Index == markedIndex)
                    {
                        TextRenderer.DrawText(e.Graphics, GetItemText(Items[e.Index]), Font, e.Bounds, Color.Red, flags);
                    }
                    
                    // Other Items (Except Marked)
                    else
                    {
                        TextRenderer.DrawText(e.Graphics, GetItemText(Items[e.Index]), Font, e.Bounds, Color.White, flags);
                    }
                }
            }

            // Draw Unselected:
            else
            {
                using (var brush = new SolidBrush(BackColor))
                using (var markedBrush = new SolidBrush(Color.Khaki))
                {
                    e.Graphics.FillRectangle(brush, e.Bounds);
                    TextRenderer.DrawText(e.Graphics, GetItemText(Items[e.Index]), Font, e.Bounds, Color.White, flags);
                }

                // Draw (Unselected) Marked Item
                if (markedIndex > -1 && e.Index == markedIndex)
                {
                    TextRenderer.DrawText(e.Graphics, GetItemText(Items[e.Index]), Font, e.Bounds, Color.Red, flags);
                }
            }

            e.DrawFocusRectangle();

            base.OnDrawItem(e);
        }

        // Set the Height of the Item (Width: only if needed).
        // This is the Standard Value (Modify as required)
        protected override void OnMeasureItem(MeasureItemEventArgs e)
        {
            if (Items.Count > 0)
            {
                e.ItemHeight = Font.Height + 4; // 4 = Text vs Item Rectangle Margin
            }

            base.OnMeasureItem(e);
        }

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

        protected override void OnDoubleClick(EventArgs e)
        {
            base.OnDoubleClick(e);

            SetMarkedItem();
        }

        protected override void OnMouseDoubleClick(MouseEventArgs e)
        {
            base.OnMouseDoubleClick(e);

            if (e.Button == MouseButtons.Left)
            {
                SetMarkedItem();
            }
        }
        #endregion

        #region <Methods>
        /// <summary>
        /// WndProc is Overridden in order to Intercept the LB_RESETCONTENT (sent when the ObjectCollection is cleared);<br/> 
        /// and the LB_DELETESTRING (sent when an Item is removed).
        /// This is done to reset the marked Item when the list is cleared or the marked Item is removed (otherwise an Item will remain marked when it shouldn't).
        /// </summary>
        /// <param name="m"></param>
        //protected override void WndProc(ref Message m)
        //{
        //    switch (m.Msg)
        //    {
        //        // List Cleared
        //        case LB_RESETCONTENT:
        //            markedIndex = -1;
        //            break;

        //        // Item Deleted
        //        case LB_DELETESTRING:
        //            if (markedIndex == m.WParam.ToInt32())
        //            {
        //            markedIndex = -1;
        //            }
        //            break;
        //    }
        //}

        private void SetMarkedItem()    // Current Block
        {
            markedIndex = SelectedIndex;
        }

        // Previous Code Line (By Jimmy; using Ternary Operator) <----------------------------------------
        //private void SetMarkedItem() => MarkedIndex = markedIndex == SelectedIndex ? -1 : SelectedIndex;
        #endregion
    }
}

有用的相关内容

ListBox : Pinvoke LB_(Enums)

How to add multiline Text to a ListBox item

Answer 1

此示例 class 包含使列表作为标准列表框工作所需的调整，但具有问题中描述的 增强功能 。
另请参阅代码中的注释。

TextRenderer.DrawText() 替换 Graphics.DrawString()：这将为呈现的列表项提供更 自然的 方面。无需使用 anti-aliasing.
OnMeasureItem 也被覆盖，为项目提供自定义高度（可选的宽度 - 当严格要求时）。它设置为 ListBox.Font.Height + 4 （相当标准）；根据需要修改。
OnDrawItem() 已更正以处理自定义选择颜色和标记项目的颜色。请注意，此方法对每个 Item 调用一次，因此您不必每次都循环整个集合，只需将当前 Item 涂上正确的颜色即可。
SetMarkedItem() 被修改为切换标记项目的状态，以防你 double-click 它两次。
WndProc 被覆盖为 intercept LB_RESETCONTENT（在清除 ObjectCollection 时发送）和 LB_DELETESTRING（在清除 ObjectCollection 时发送一个项目被删除）。这样做是为了在清除列表或删除标记的项目时重置标记的项目（否则项目将在不应该标记的情况下保持标记）。
设置属性值时，在调用 Invalidate()（或任何其他方法 - 或属性之前，请始终验证新值不等于旧值setter) 无缘无故。
一些小改动，见代码。

public class MyPlaylist : ListBox {

    private const int LB_DELETESTRING = 0x0182;
    private const int LB_RESETCONTENT = 0x0184;

    TextFormatFlags flags = TextFormatFlags.PreserveGraphicsClipping |
                            TextFormatFlags.LeftAndRightPadding |
                            TextFormatFlags.VerticalCenter;

    public MyPlaylist()
    {
        SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
        DrawMode = DrawMode.OwnerDrawVariable;
    }

    protected override void WndProc(ref Message m)
    {
        switch (m.Msg) {
            // List cleared
            case LB_RESETCONTENT:
                markedIndex = -1;
                break;
            // Item deleted
            case LB_DELETESTRING:
                if (markedIndex == m.WParam.ToInt32()) {
                    markedIndex = -1;
                }
                break;
        }
        base.WndProc(ref m);
    }

    private int markedIndex = -1;
    public int MarkedIndex {
        get => markedIndex;
        set {
            if (value != markedIndex) {
                markedIndex = value;
                Invalidate();
            }
        }
    }

    // Read-only: just return the marked Item, set it using the Index only
    public object MarkedItem {
        get => Items[markedIndex];
    }

    // Always verify that the new value is different from the old one
    private Color markedItemForeColor = Color.Orange;
    public Color MarkedItemForeColor {
        get => markedItemForeColor;
        set { 
            if (value != markedItemForeColor) {
                markedItemForeColor = value;
                Invalidate();
            }
        }
    }

    private Color markedItemBackColor = Color.DimGray;
    public Color MarkedItemBackColor {
        get => markedItemBackColor;
        set { 
            if (value != markedItemBackColor) {
                markedItemBackColor = value;
                Invalidate();
            }
        }
    }

    private Color selectionBackColor = Color.DeepSkyBlue;
    public Color SelectionBackColor {
        get => selectionBackColor;
        set { 
            if (value != selectionBackColor) {
                selectionBackColor = value;
                Invalidate();
            }
        }
    }

    private Color selectionForeColor = Color.White;
    public Color SelectionForeColor {
        get => selectionForeColor;
        set { 
            if (value != selectionForeColor) {
                selectionForeColor = value;
                Invalidate();
            }
        }
    }

    // Use TextRenderer to draw the Items - no anti-aliasing needed
    protected override void OnDrawItem(DrawItemEventArgs e)
    {
        if (Items.Count == 0) return;
        if (e.State.HasFlag(DrawItemState.Focus) || e.State.HasFlag(DrawItemState.Selected)) {
            using (var brush = new SolidBrush(selectionBackColor)) {
                e.Graphics.FillRectangle(brush, e.Bounds);
            }
            TextRenderer.DrawText(e.Graphics, GetItemText(Items[e.Index]), Font, e.Bounds, selectionForeColor, flags);
        }
        else {
            var color = markedIndex != -1 && markedIndex == e.Index ? markedItemBackColor : BackColor;
            using (var brush = new SolidBrush(color)) {
                e.Graphics.FillRectangle(brush, e.Bounds);
            }
            var foreColor = markedIndex == e.Index ? markedItemForeColor : ForeColor;
            TextRenderer.DrawText(e.Graphics, GetItemText(Items[e.Index]), Font, e.Bounds, foreColor, flags);
        }
        e.DrawFocusRectangle();
        base.OnDrawItem(e);
    }

    // Set the Height (the Width only if needed) of the Item
    // This is the standard value, modify as required
    protected override void OnMeasureItem(MeasureItemEventArgs e)
    {
        if (Items.Count > 0) {
            e.ItemHeight = Font.Height + 4;
        }
        base.OnMeasureItem(e);
    }

    protected override void OnMouseDoubleClick(MouseEventArgs e)
    {
        if (e.Button == MouseButtons.Left) {
            SetMarkedItem();
        }
        base.OnMouseDoubleClick(e);
    }

    private void SetMarkedItem() => MarkedIndex = markedIndex == SelectedIndex ? -1 : SelectedIndex;
}

ListBox 更改特定项目的前景色

ListBox Change a Specific Item ForeColor

c#

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winforms