如何自定义绘制一个TextBox保证金？ [英] How to custom-draw a margin in a TextBox?

问题描述

我要画一个边界线在一个WinForms TextBox中80个字符。下面是我尝试过，在我的文本框的子类：

I want to draw a margin line at 80 characters in a WinForms TextBox. Here is what I've tried, in my TextBox subclass:

protected override void WndProc(ref Message m)
{
    base.WndProc(ref m);

    const int WM_PAINT = 0x00F;
    if (m.Msg == WM_PAINT) {
        DrawMargin();
    }
}

void DrawMargin()
{
    using (Pen pen = new Pen(Color.Gray, 1)) {
        using (Graphics graphics = CreateGraphics()) {
            float charWidth = graphics.MeasureString("M", Font).Width;
            graphics.DrawLine(pen, charWidth * 80, 0, charWidth * 80, Height);
        }
    }
}

有至少有三个问题是：

1. 当用户输入一些文字，该行的一部分被冲压出来（变白）。
2. 当用户用鼠标选择一些文本，在上述情况发生一次。
当文本框滚动
3. 在该行闪烁。

我注意到，TED记事本（它使用一个Win32编辑控制）是能够利用的余量没有任何问题，所以它似乎有可能做我想做的。谁能告诉我如何？

I notice that TED Notepad (which uses a Win32 EDIT control) is able to draw a margin without any problems, so it seems that it's possible to do what I want. Could anyone advise me how?

推荐答案

据我所知，这样做的最好的方法就是把一个WinForms.Panel在文本框：

As far as I can tell, the best way of doing this is simply to place a WinForms.Panel over the TextBox:

class FooTextBox : TextBox
{
    public FooTextBox()
    {
        margin = new Panel();

        margin.Enabled   = false;
        margin.BackColor = Color.LightGray;
        margin.Top       = 0;
        margin.Height    = ClientSize.Height;
        margin.Left      = <whatever>;
        margin.Width     = 1;

        Controls.Add(margin);
    }

    Panel margin;
}

由于面板未启用，它没有考虑鼠标输入

Since the panel is not Enabled, it doesn't take mouse input.

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