How to use RichTextBox.SelectionColor property to identify multiple text's background colors in C#?

Question

I have a RichTextBox. I'm trying to code so that if a specific color is found in the SelectionBackColor property of the RTB, the background color of the words/ texts to be removed. For that, I need to detect if there exists multiple colors in the RTB. However, according to the documentation,

If the current text selection has more than one color specified, this property returns Color.Empty.

---

This is what I've tried so far:

private void randomBtn_Click(object sender, EventArgs e)
{
    int startIndex = 0; //start from beginning of the richTextBox1
    int endIndex = this.richTextBox1.TextLength; //until the end of all text available
    this.richTextBox1.Select(startIndex, endIndex); //select from start until the end

    if(endIndex != 0)
    {
        for(int i=startIndex; i< endIndex; i++)
        {
            if (this.richTextBox1.Text[i].ToString().Contains(" ")) //skips white spaces
            {
                continue;
            }
            else
            {
                while ((this.richTextBox1.BackColor != Color.Empty))
                {
                    if (this.richTextBox1.SelectionBackColor.R == 155 && this.richTextBox1.SelectionBackColor.G == 255 && this.richTextBox1.SelectionBackColor.B == 255)
                    {
                        this.richTextBox1.HideSelection = true; //to prevent text highlighted
                        MessageBox.Show(this, "Texts with RGB(155, 255, 255) found!", "", MessageBoxButtons.OK);
                        break;
                    }
                    else
                    {
                        this.richTextBox1.HideSelection = true;
                        MessageBox.Show(this, "Error!", "", MessageBoxButtons.OK);
                        break;
                    }
                }
            }
        }
    }
    else
    {
        MessageBox.Show(this, "richTextBox1 is empty!", "Alert!", MessageBoxButtons.OK);
    }
}

To test, I added a breakpoint at the code containing the while line. Below shows the success and fail criterion,

The code works if:

• There is no whitespace(at all)
• There is only one color in the RTB

The code fails if:

• There are whitespaces in between texts/ words/ characters
• There are multiple colors in the RTB

---

Below shows the program execution examples:

This is when only one color is applied in the RTB(success),

This is when only one color and a whitespace are applied in the RTB(fail),

This is when multiple colors and whitespaces are applied in the RTB(fail),

---

So, is there any ways to override the return value of the SelectionColor property to be able to detect multiple colors, or are there any other ways of doing this? Just so you know, I've searched for this kind of problem over the internet, but I didn't think I've find any related issues.

Answer 1

It took me a while to figure out what @TaW meant in the comment section, but thanks to him, I've managed to solve this issue.

Actually, based on my reply in the comment section that I asked @TaW, what I thought as the same concept, was actually wrong. In the post above, what I did was entirely wrong:

1. I was supposed to assess each text one by one to know what their colors are. However, the codes below were already wrong to begin with.:

int startIndex = 0;
int endIndex = this.richTextBox1.TextLength;
this.richTextBox1.Select(startIndex, endIndex);

2. To analyze how RTB.SelectionColor, RTB.SelectionStart, and RTB.SelectionLength work, I decided to create another project. The project is a simple program containing an RTB, and some other buttons to manage the RTB's SelectionColor. If you want to check for the project that I've done, you're always welcomed to visit this link.

From "2", I re-used all the codes to suit the original project that I was working on. Now, it's all fine and working as it should.

---

To note, there are two important concepts/ ideas on managing the Selection property of the RTB.

1. If you are concerned of assessing each and every text in the RTB, you should code it like this:

private void methodA(RichTextBox localRTB)
{
    //go through text one by one
    int startIndex = 0;
    int endIndex = localRTB.TextLength;
    localRTB.SelectionStart = startIndex;
    localRTB.SelectionLength = 1; //always 1 'cuz we want to assess each text one by one

    while (localRTB.SelectionStart < endIndex)
    {
        //if the SelectionBackColor is red, change it to white
        if (localRTB.SelectionBackColor == Color.Red) //take red color for example
        {
            localRTB.SelectionBackColor = Color.White;
        }
        //--manage bg color of selected text in RTB--

        //so that able to go to next text
        localRTB.SelectionStart += 1;
    }

    //finally...
    localRTB.DeselectAll(); //unselect text in RTB
    localRTB.Select(); //set focus back to the RTB
}

Below shows the result of the codes above(1):

2. If you don't really care about assessing each and every text in the RTB, you should code it like this instead:

private void methodB(RichTextBox localRTB)
{
    int startIndex;
    int endIndex;

    if (localRTB.SelectionLength.Equals(0)) //if user don't select any text
    {
        startIndex = 0; //from beginning of RTB
        endIndex = localRTB.TextLength; //'til the end of RTB

        //--manage selected text in the RTB--
        localRTB.SelectionStart = startIndex;
        localRTB.SelectionLength = endIndex;

        localRTB.Select(localRTB.SelectionStart, localRTB.SelectionLength);
        //--manage selected text in the RTB--
    }
    else if (!(localRTB.SelectionLength.Equals(0))) //if user has text selected
    {
        startIndex = localRTB.SelectionStart; //from beginning of RTB
        endIndex = localRTB.SelectionLength; //'til the end of RTB

        if (localRTB.SelectedText.Contains(" ")) //skips whitespaces if selected together with text
        {
            if (localRTB.SelectedText.EndsWith(" "))
            {
                endIndex -= 1;
            }
        }

        //--manage selected text in the RTB--
        localRTB.Select(startIndex, endIndex);
        //--manage selected text in the RTB--
    }
}

Below shows the result of the codes above(2):

Peace...??