代码并不总是突出显示richtextbox中的选定文本

Question

richTextBox1 contains text I click on a word and Console displays that word for me and it highlights/selects the word i clicked on.

To do this, I keep the index of the character I clicked on then go left and right until I hit a space, -1, or end of file. Now I have the indexes of the beginning and end of the word. The last two lines are supposed to select the word between those two indexes.

However, what happens is that sometimes it highlights the word I want and sometimes it highlights all the words to the right of the character I clicked on.

"omar hello where are you going"
If I click on h in hello, it highlights hello where instead of highlighting hello
If I click on o in going, it will highlight going only as it should
If I click on o in you, it will highlight you going

I used console to check the start and end indexes of the word and they're always right yet for some reason, other words are selected in addition to the word i clicked on

private void richTextBox1_Click(object sender, EventArgs e)
{
    int length = richTextBox1.Text.Length;
    int rightPart = richTextBox1.SelectionStart;
    int leftPart = richTextBox1.SelectionStart - 1;
    string rightText = "";
    string leftText = "";

    while (rightPart != length)
    {
        if (richTextBox1.Text[rightPart].ToString().CompareTo(" ") != 0)
        {
            rightText += richTextBox1.Text[rightPart];
            rightPart++;
        }

        else
        {
            break;
        }
    }

    while (leftPart != -1)
    {
        if (richTextBox1.Text[leftPart].ToString().CompareTo(" ") != 0)
        {
            leftText = richTextBox1.Text[leftPart] + leftText;
            leftPart--;
        }

        else
        {
            break;
        }
    }

    leftPart++;
    Console.WriteLine("\nSelected word is " + leftText + rightText + "\n");

    richTextBox1.SelectionStart = leftPart;
    richTextBox1.SelectionLength = rightPart;       
}

Answer 1

The problem appears to be that you are setting the SelectionLength equal to rightPart . Remember this property represents the length of the selection, not the last index of the selection.

Instead, try changing your code to calculate the length by getting the difference between leftPart and rightPart :

richTextBox1.SelectionLength = rightPart - leftPart;

---

For what it's worth, your code can be shortened a little:

private void richTextBox1_Click(object sender, EventArgs e)
{
    if (richTextBox1.TextLength == 0) return;
    int rightPart = richTextBox1.SelectionStart;
    int leftPart = richTextBox1.SelectionStart - 1;

    while (rightPart < richTextBox1.TextLength && richTextBox1.Text[rightPart] != ' ') 
    {
        rightPart++;
    }

    while (leftPart > -1 && richTextBox1.Text[leftPart] != ' ') 
    {
        leftPart--;
    }

    leftPart++;

    Console.WriteLine($"\nSelected word is " + 
        richTextBox1.Text.Substring(leftPart, rightPart - leftPart) + "\n");

    richTextBox1.SelectionStart = leftPart;
    richTextBox1.SelectionLength = rightPart - leftPart;
}

---

Or even a little more, using IndexOf and LastIndexOf instead of loops to find the spaces:

private void richTextBox1_Click(object sender, EventArgs e)
{
    if (richTextBox1.TextLength == 0) return;

    // Find the space before this word and after this word
    var selStart = Math.Min(richTextBox1.SelectionStart, richTextBox1.TextLength - 1);
    var firstSpace = richTextBox1.Text.LastIndexOf(' ', selStart);
    var lastSpace = richTextBox1.Text.IndexOf(' ', selStart);

    var start = firstSpace + 1;
    var length = (lastSpace < 0 ? richTextBox1.TextLength : lastSpace) - start;

    Console.WriteLine($"\nSelected word is {richTextBox1.Text.Substring(start, length)} \n");

    richTextBox1.SelectionStart = start;
    richTextBox1.SelectionLength = length;
}