[原创][开源] SunnyUI.Net 开发日志：ListBox 增加跟随鼠标滑过高亮
SunnyUI.Net 开发日志：ListBox 增加跟随鼠标滑过高亮，这可是在别人两年的基础上再改进的，哈哈！~
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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。
