RichTextBox的特定行的值不变

Question

I am trying to do very simple thing which should work but unfortunately its not working.

I have a RichTextBox component on my Winform . I am trying to change text value of some lines of the RichTextBox but its not changing the value. Here is my code:

    private void button1_Click(object sender, EventArgs e)
    {
        for(int i=0; i < richTextBox1.Lines.Length; i++)
        {
            if(richTextBox1.Lines[i] == "ok")
            {
                richTextBox1.Lines[i] = "Done";
            }
        }
    }

I put break point and I notice that it executes

richTextBox1.Lines[i] = "Done";

But it does not change the value at all. Can anyone explain it? Why its not modifying the value? Is there way to change/modify the value as per Line?

Thanks and Regards

Answer 1

According to MSDN ( TextBoxBase.Lines Property ):

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 you better go for:

for (int i = 0; i < richTextBox1.Lines.Length; i++)
{
    if (richTextBox1.Lines[i] == "ok")
    {
        string[] lines = richTextBox1.Lines;
        lines[i] = "done";
        richTextBox1.Lines = lines;
    }
}

UPDATE: another way of doing this (that I do not recommend though):

string line = richTextBox1.Lines[i]; 
richTextBox1.Find(line);
richTextBox1.SelectedText = "done";