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  • C#教程之[原创][开源] SunnyUI.Net 开发日志：ListBox 增加跟随鼠标滑过高亮(4)

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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：

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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);
        }
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