How to Color Different Parts of a String in a C# RichTextBox?

Colorize different parts of RichTextBox string in C#

In the field of C# programming, it is a very practical function to enhance the visualization effect of RichTextBox by adding colored text. Let's say you crafted a string with different parts, each part should have its own unique color. The goal is to seamlessly add this multi-colored string to your RichTextBox and paint the individual elements with the specified color.

To achieve this, a clever solution emerged: an extension method called AppendText, which adds a color parameter. This method elegantly embeds the specified text into a RichTextBox, decorated with the selected color.

public static class RichTextBoxExtensions
{
    public static void AppendText(this RichTextBox box, string text, Color color)
    {
        // 将光标定位到文本末尾
        box.SelectionStart = box.TextLength;

        // 确保当前没有选中任何文本
        box.SelectionLength = 0;

        // 设置文本颜色
        box.SelectionColor = color;

        // 追加文本
        box.AppendText(text);

        // 将文本颜色重置为默认值
        box.SelectionColor = box.ForeColor;
    }
}

With this extension method, using it is as easy as creating your masterpiece:

var userid = "USER0001";
var message = "Access denied";
var box = new RichTextBox
{
    Dock = DockStyle.Fill,
    Font = new Font("Courier New", 10)
};

// 以红色追加时间
box.AppendText("[" + DateTime.Now.ToShortTimeString() + "]", Color.Red);

// 添加空格
box.AppendText(" ");

// 以绿色打印用户ID
box.AppendText(userid, Color.Green);

// 添加冒号
box.AppendText(": ");

// 以蓝色显示消息
box.AppendText(message, Color.Blue);

// 追加换行符
box.AppendText(Environment.NewLine);

// 创建窗体并显示RichTextBox
new Form { Controls = { box } }.ShowDialog();

This code neatly demonstrates how to append each part of a string along with its assigned color, creating a visually appealing and informative RichTextBox.

It is worth noting that if you are experiencing flickering issues when outputting large amounts of messages, the C# Corner article linked below provides valuable insight on how to mitigate this behavior:

Reduce RichTextBox flickering

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