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SunnyUI.Net 開發日誌：ListBox 增加跟隨鼠標滑過高亮
QQ羣裏，寸木說，ListBox鼠標移動時，當前行需要焦點，我想了想，不難實現啊
不就是在鼠標移動時重繪Item嘛，何況選中的Item已經改了顏色了。
見UIListBox代碼：
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 選中行狀態嘛
看了e.State有e.State == DrawItemState.HotLight，不就是高亮的麼，於是開始擼代碼，加狀態判斷
Run
暈。。。沒變，這HotLight不起作用，好吧，問度娘。。。
翻山越嶺，跋山涉水。。。
找到這篇：https://www.jb51.cc/csharp/101121.html
其中提到：
我在我的WinForms應用程序中使用OwnerDrawFixed作爲DrawMode用於自定義ListBox控件.當用戶將鼠標懸停在列表框項目上時,我希望重新繪製ListBoxItem的背景(或執行其他操作),即在MouseMove …DrawItemState.HotLight永遠不適用於ListBox,所以我想知道如何模擬它,如何解決這個問題.
DrawItemState.HotLight永遠不適用於ListBox，是永遠。。。怎麼這麼遠。。。
繼續往下看：
解決方法
DrawItemState.HotLight僅適用於所有者繪製的菜單,而不適用於列表框.對於ListBox,您必須自己跟蹤項目：
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();
}
}
}
兄弟們，人家這花兩年時間解決的，應該有用，繼續再找找，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，也是兩年，估計上面中文的從這個翻譯過來。
除了這倆，還真沒找到。
繼續擼代碼，果真管用。不過還是有問題，鼠標滑快了，ListBox閃爍的厲害。
分析代碼 listBox1.Invalidate(); 這是刷新全部的。鼠標滑過也就和本次選中和上次選中的有關係。
就刷這兩個Item就行，有了思路，擼代碼三連發：
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)
第一個參數Graphics，也找了一會兒，後來看這篇：
https://www.cnblogs.com/yuanyeguhong/archive/2013/09/20/3330606.html
其實就是Graphics對象的DrawString方法，而參數e中的Graphics是如何來的呢。
我們接着分析DrawItemEventArgs這個類，他既然是對listBox1某一項的屬性的打包，
那麼我估計其中的Graphics對象就是由listBox1.creatgraphics而來的。
好了，到此我們就可以自定義重繪listbox某項的函數了，可任意調用的哦！
好了，至此，問題都已找到答案，再捋一下思路，把邏輯理順。擼代碼，調試，OK！！！
主要代碼如下：
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咱也給實現了，DrawItemState.Grayed 我是隨便選的狀態，區別於其他。
想看全部代碼，看我的開源項目吧，https://gitee.com/yhuse/SunnyUI ，哎，客官別走嘛，點個Star先。