OwnerDrawVariable组合框下拉空白 [英] OwnerDrawVariable Combobox DropDown Blank Space

问题描述

我开发了以下自定义组合框来增加项目的高度。一旦完成，当有一个滚动条时，在下拉菜单的末尾出现一个空白。

如何解决问题？

  class MyComboBoxXX：ComboBox 
 {
 public MyComboBoxXX（）：base（）
 {
 .DrawMode = DrawMode.OwnerDrawVariable; 
 this.DropDownStyle = ComboBoxStyle.DropDownList; 
 this.MaxDropDownItems = 5; 
 this.IntegralHeight = false; 
} 
 
 protected override void OnMeasureItem（MeasureItemEventArgs e）
 {
 e.ItemHeight = 40; 
 this.DropDownHeight = 40 * 5; 
} 
 protected override void OnDrawItem（DrawItemEventArgs e）
 {
 e.DrawBackground（）; 
 var index = e.Index; 
 if（index< 0 || index> = Items.Count）return; 
使用（var brush = new SolidBrush（e.ForeColor））
 {
 Rectangle rec = new Rectangle（e.Bounds.Left，e.Bounds.Top +（（e.Bounds。 Height  -  ItemHeight）/ 2），e.Bounds.Width，ItemHeight）; 
 e.Graphics.DrawString（this.Items [e.Index] .ToString（），e.​​Font，new SolidBrush（this.ForeColor），rec）; 
} 
 e.DrawFocusRectangle（）; 
} 
} 
  

解决方案

你仔细观察，看起来DropDown区域在顶部有一个1像素的边界，也在底部。您可以通过向 DropDownHeight 添加2个像素来消除空格。

  protected override void OnMeasureItem（MeasureItemEventArgs e）
 {
 e.ItemHeight = 40; 
 this.DropDownHeight =（40 * 5）+ 2; // add 2 pixels to include the border 
} 
  

>
结果：

I have developed the following custom combo box to increase the height of the items. Once that is done, a blank space appears at the end of the drop down menu when there is a scrollbar. How can I correct the issue?

class MyComboBoxXX : ComboBox
{
    public MyComboBoxXX():base()
    {
        this.DrawMode = DrawMode.OwnerDrawVariable;
        this.DropDownStyle = ComboBoxStyle.DropDownList;
        this.MaxDropDownItems = 5;
        this.IntegralHeight = false;         
    }

    protected override void OnMeasureItem(MeasureItemEventArgs e)
    {
        e.ItemHeight = 40;
        this.DropDownHeight = 40 * 5;        
    }
    protected override void OnDrawItem(DrawItemEventArgs e)
    {        
        e.DrawBackground();        
        var index = e.Index;    
        if (index < 0 || index >= Items.Count) return;    
        using (var brush = new SolidBrush(e.ForeColor))
        {            
            Rectangle rec = new Rectangle(e.Bounds.Left, e.Bounds.Top + ((e.Bounds.Height - ItemHeight) / 2), e.Bounds.Width, ItemHeight);
            e.Graphics.DrawString(this.Items[e.Index].ToString(), e.Font, new SolidBrush(this.ForeColor), rec);
        }
        e.DrawFocusRectangle();
    }    
}

解决方案

If you look closely, it appears that the DropDown area has a 1 pixel border at the top, and also at the bottom. You can get rid of the space by adding 2 pixels to the DropDownHeight.

protected override void OnMeasureItem(MeasureItemEventArgs e)
{
    e.ItemHeight = 40;
    this.DropDownHeight = (40 * 5) + 2; //add 2 pixels to include the border
}

Result:

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