[原创][开源] SunnyUI.Net 开发日志：ListBox 增加跟随鼠标滑过高亮

SunnyUI.Net, 基于 C# .Net WinForm 开源控件库、工具类库、扩展类库、多页面开发框架

• Blog: https://www.cnblogs.com/yhuse
• Gitee: https://gitee.com/yhuse/SunnyUI
• GitHub: https://github.com/yhuse/SunnyUI
• SunnyUI.Net 系列文章目录
• 欢迎交流，QQ群：56829229 (SunnyUI技术交流群)

SunnyUI.Net 开发日志：ListBox 增加跟随鼠标滑过高亮

QQ群里，寸木说，ListBox鼠标移动时，当前行需要焦点，我想了想，不难实现啊

不就是在鼠标移动时重绘Item嘛，何况选中的Item已经改了颜色了。

见UIListBox代码：

protected override void OnDrawItem(DrawItemEventArgs e)
        {
            base.OnDrawItem(e);
            BeforeDrawItem?.Invoke(this, Items, e);
            if (Items.Count == 0)
            {
                return;
            }

            e.DrawBackground();

            if (e.Index < 0 || e.Index >= Items.Count)
            {
                return;
            }

            StringFormat sStringFormat = new StringFormat();
            sStringFormat.LineAlignment = StringAlignment.Center;

            Color backColor = (e.State & DrawItemState.Selected) == DrawItemState.Selected ? ItemSelectBackColor : BackColor;
            Color foreColor = (e.State & DrawItemState.Selected) == DrawItemState.Selected ? ItemSelectForeColor : ForeColor;

            Rectangle rect = new Rectangle(e.Bounds.X, e.Bounds.Y, e.Bounds.Width - 1, e.Bounds.Height - 1);
            e.Graphics.FillRectangle(BackColor, e.Bounds);
            e.Graphics.FillRoundRectangle(backColor, rect, 5);
            e.Graphics.DrawString(Items[e.Index].ToString(), e.Font, foreColor, e.Bounds, sStringFormat);
        }

看：(e.State & DrawItemState.Selected) == DrawItemState.Selected 选中行状态嘛

看了e.State有e.State == DrawItemState.HotLight，不就是高亮的么，于是开始撸代码，加状态判断

Run

晕。。。没变，这HotLight不起作用，好吧，问度娘。。。

翻山越岭，跋山涉水。。。

找到这篇：https://www.jb51.cc/csharp/101121.html

其中提到：

   我在我的WinForms应用程序中使用OwnerDrawFixed作为DrawMode用于自定义ListBox控件.当用户将鼠标悬停在列表框项目上时,我希望重新绘制ListBoxItem的背景(或执行其他操作),即在MouseMove …DrawItemState.HotLight永远不适用于ListBox,所以我想知道如何模拟它,如何解决这个问题.

DrawItemState.HotLight永远不适用于ListBox，是永远。。。怎么这么远。。。

继续往下看：

解决方法

我花了两年时间为你找到答案,但这里是：

DrawItemState.HotLight仅适用于所有者绘制的菜单,而不适用于列表框.对于ListBox,您必须自己跟踪项目：

public partial class Form1 : Form
{
  private int _MouseIndex = -1;

  public Form1()
  { InitializeComponent(); }

  private void listBox1_DrawItem(object sender,DrawItemEventArgs e)
  {
    Brush textBrush = SystemBrushes.WindowText;

    if (e.Index > -1)
    {
      if (e.Index == _MouseIndex)
      {
        e.Graphics.FillRectangle(SystemBrushes.HotTrack,e.Bounds);
        textBrush = SystemBrushes.HighlightText;
      }
      else
      {
        if ((e.State & DrawItemState.Selected) == DrawItemState.Selected)
        {
          e.Graphics.FillRectangle(SystemBrushes.Highlight,e.Bounds);
          textBrush = SystemBrushes.HighlightText;
        }
        else
          e.Graphics.FillRectangle(SystemBrushes.Window,e.Bounds);
      }
      e.Graphics.DrawString(listBox1.Items[e.Index].ToString(),e.Font,textBrush,e.Bounds.Left + 2,e.Bounds.Top);
    }
  }

  private void listBox1_MouseMove(object sender,MouseEventArgs e)
  {
    int index = listBox1.IndexFromPoint(e.Location);
    if (index != _MouseIndex)
    {
      _MouseIndex = index;
      listBox1.Invalidate();
    }
  }

  private void listBox1_MouseLeave(object sender,EventArgs e)
  {
    if (_MouseIndex > -1)
    {
      _MouseIndex = -1;
      listBox1.Invalidate();
    }
  }
}

兄弟们，人家这花两年时间解决的，应该有用，继续再找找，又找到一篇洋文的：

https://stackoverflow.com/questions/1316027/listbox-drawitem-hotlight-state-in-the-ownerdraw-mode

It took me only two years to find the answer for you, but here it is:

The DrawItemState.HotLight only applies to owner drawn menus, not the listbox.

For the ListBox, you have to keep track of the item yourself:

看看，也是两年，估计上面中文的从这个翻译过来。

除了这俩，还真没找到。

继续撸代码，果真管用。不过还是有问题，鼠标滑快了，ListBox闪烁的厉害。

分析代码  listBox1.Invalidate(); 这是刷新全部的。鼠标滑过也就和本次选中和上次选中的有关系。

就刷这两个Item就行，有了思路，撸代码三连发：

        private int lastIndex = -1;
        private int mouseIndex = -1;

        [Browsable(false)]
        public int MouseIndex
        {
            get => mouseIndex;
            set
            {
                if (mouseIndex != value)
                {
                    if (lastIndex >= 0 && lastIndex != SelectedIndex)
                    {
                        OnDrawItem(new DrawItemEventArgs(this.CreateGraphics(), Font, GetItemRectangle(lastIndex), lastIndex, DrawItemState.Grayed));
                    }

                    mouseIndex = value;
                    if (mouseIndex >= 0 && mouseIndex != SelectedIndex)
                    {
                        OnDrawItem(new DrawItemEventArgs(this.CreateGraphics(), Font, GetItemRectangle(value), value, DrawItemState.HotLight));
                    }

                    lastIndex = mouseIndex;
                }
            }
        }

        protected override void OnMouseMove(MouseEventArgs e)
        {
            base.OnMouseMove(e);
            MouseIndex = IndexFromPoint(e.Location);
        }

        protected override void OnMouseLeave(EventArgs e)
        {
            base.OnMouseLeave(e);
            MouseIndex = -1;
        }

其中 new DrawItemEventArgs(this.CreateGraphics(), Font, GetItemRectangle(value), value, DrawItemState.HotLight)

第一个参数Graphics，也找了一会儿，后来看这篇：

https://www.cnblogs.com/yuanyeguhong/archive/2013/09/20/3330606.html

其实就是Graphics对象的DrawString方法，而参数e中的Graphics是如何来的呢。
我们接着分析DrawItemEventArgs这个类，他既然是对listBox1某一项的属性的打包，
那么我估计其中的Graphics对象就是由listBox1.creatgraphics而来的。
好了，到此我们就可以自定义重绘listbox某项的函数了，可任意调用的哦！

好了，至此，问题都已找到答案，再捋一下思路，把逻辑理顺。撸代码，调试，OK！！！

主要代码如下：

protected override void OnDrawItem(DrawItemEventArgs e)
        {
            base.OnDrawItem(e);

            BeforeDrawItem?.Invoke(this, Items, e);
            if (Items.Count == 0)
            {
                return;
            }

            bool otherState = e.State == DrawItemState.Grayed || e.State == DrawItemState.HotLight;
            if (!otherState)
            {
                e.DrawBackground();
            }

            if (e.Index < 0 || e.Index >= Items.Count)
            {
                return;
            }

            StringFormat sStringFormat = new StringFormat();
            sStringFormat.LineAlignment = StringAlignment.Center;

            bool isSelected = (e.State & DrawItemState.Selected) == DrawItemState.Selected;
            Color backColor = isSelected ? ItemSelectBackColor : BackColor;
            Color foreColor = isSelected ? ItemSelectForeColor : ForeColor;

            Rectangle rect = new Rectangle(e.Bounds.X, e.Bounds.Y, e.Bounds.Width - 1, e.Bounds.Height - 1);
            if (!otherState)
            {
                e.Graphics.FillRectangle(BackColor, e.Bounds);
                e.Graphics.FillRoundRectangle(backColor, rect, 5);
                e.Graphics.DrawString(Items[e.Index].ToString(), e.Font, foreColor, e.Bounds, sStringFormat);
            }
            else
            {
                if (e.State == DrawItemState.Grayed)
                {
                    backColor = BackColor;
                    foreColor = ForeColor;
                }

                if (e.State == DrawItemState.HotLight)
                {
                    backColor = HoverColor;
                    foreColor = ForeColor;
                }

                e.Graphics.FillRectangle(BackColor, e.Bounds);
                e.Graphics.FillRoundRectangle(backColor, rect, 5);
                e.Graphics.DrawString(Items[e.Index].ToString(), e.Font, foreColor, e.Bounds, sStringFormat);
            }

            AfterDrawItem?.Invoke(this, Items, e);
        }

看，DrawItemState.HotLight咱也给实现了，DrawItemState.Grayed 我是随便选的状态，区别于其他。

想看全部代码，看我的开源项目吧，https://gitee.com/yhuse/SunnyUI ，哎，客官别走嘛，点个Star先。

原创文章，转载请保留链接 Sunny's blog