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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
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。