如何在richTextBox的索引0中的每一行附近添加数字？

Question

for (int i = 0; i < richTextBox2.Lines.Length; i++)
{
    richTextBox2.Lines[i] = richTextBox2.Lines[i].Insert(0, i + " ");
}

Before that tried with the Insert:

richTextBox2.Lines[i].Insert(0, i + " ");

In both cases it's not adding any numbers.

For example if the lines are:

Hello world
Hi
Hello

Then i want it to be now:

1 Hello world
2 Hi
3 Hello

But the loop does nothing it's not adding any numbers.

Answer 1

You can't modifiy the single line in that way. If you look at MSDN you will find this remark

By default, the collection of lines is a read-only copy of the lines in the TextBox. To get a writable collection of lines, use code similar to the following: textBox1.Lines = new string[] { "abcd" };

So the correct way to reach you goal is

string[]  lines = richTextBox2.Lines;

for (int i = 0; i < lines.Length; i++)
{
    lines[i] = (i+1) + " " + lines[i];
}
richTextBox2.Lines = lines;

Answer 2

You can try using Linq :

using System.Linq;

...

richTextBox2.Lines = richTextBox2
  .Lines
  .Select((line, index) => $"{index + 1} {line}")
  .ToArray();

please, avoid redrawing UI (esp. RichTextBox ) which can slow down your application, but build the data (lines, text) and then assign it in one go .