覆盖ListBox的DrawItem - 未选中的项目不重绘 [英] Overriding DrawItem for ListBox - unselected items are not redrawn

问题描述

这是一个C＃桌面应用程序。我的 ListBox的 DrawStyle 属性设置为 OwnerDrawFixed 。

This is a C# desktop application. The DrawStyle property of my ListBox is set to OwnerDrawFixed.

问题：我重写DRAWITEM在不同的字体绘制文本，和它的作品。但是当我开始调整在运行时的形式，所选择的项目是正确绘制的，但他们的休息都没有重绘，导致文本寻找未选定项目已损坏。

The problem: I override DrawItem to draw text in different fonts, and it works. But when I start resizing the form at the runtime, the selected item is drawn correctly, but the rest of them are not redrawn, causing text looking corrupt for unselected items.

这里是我的代码：

private void listDevices_DrawItem(object sender, DrawItemEventArgs e)
{
    e.DrawBackground();

    string textDevice = ((ListBox)sender).Items[e.Index].ToString();

    e.Graphics.DrawString(textDevice,
        new Font("Ariel", 15, FontStyle.Bold), new SolidBrush(Color.Black), 
        e.Bounds, StringFormat.GenericDefault);


    // Figure out where to draw IP
    StringFormat copy = new StringFormat(
        StringFormatFlags.NoWrap |
        StringFormatFlags.MeasureTrailingSpaces
    );
    copy.SetMeasurableCharacterRanges(new CharacterRange[] {new CharacterRange(0, textDevice.Length)});

    Region[] regions = e.Graphics.MeasureCharacterRanges(
        textDevice, new Font("Ariel", 15, FontStyle.Bold), e.Bounds, copy);

    int width = (int)(regions[0].GetBounds(e.Graphics).Width);
    Rectangle rect = e.Bounds;
    rect.X += width;
    rect.Width -= width;

    // draw IP
    e.Graphics.DrawString(" 255.255.255.255",
        new Font("Courier New", 10), new SolidBrush(Color.DarkBlue),
        rect, copy);

    e.DrawFocusRectangle();
}

listDevices.Items.Add("Device001");
listDevices.Items.Add("Device002");

此外，（选择一个）是正确绘制的项目闪烁的形式调整大小。没什么大不了的，但如果有人知道为什么.... TNX

Also, the item that is drawn correctly (the selected one) is flickering on form resizing. No biggie, but if anyone know why.... tnx

推荐答案

将下面的代码在Resize事件：

Put the following code in the Resize event:

private void listDevices_Resize(object sender, EventArgs e) {
    listDevices.Invalidate();
}

这应该引起所有重绘。

要停止闪烁，则需要双缓冲。

To stop the flickering, you need double buffering.

要做到这一点，做一个新的类，从Control派生，并把在以下构造器：

To do this, make a new class, derived from ListBox, and put the following in the constructor:

this.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);

或者只是粘贴到代码文件这样的：

Or just paste this into a code file:

using System.Windows.Forms;

namespace Whatever {
    public class DBListBox : ListBox {
        public DBListBox(): base() {
            this.DoubleBuffered = true;
            // OR
            // this.SetStyle(ControlStyles.OptimizedDoubleBuffer, true);
        }
    }
}

替换什么与命名空间项目使用，或使之更有用的东西。编译后，你应该能够添加在窗体设计器DBListBox。

Replace "Whatever" with the namespace your project uses, or make it something more useful. AFter compiling, you should be able to add a DBListBox in the form designer.

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