TextBox. GetLineIndexFromCharacterIndex returns -1 when passing in large text

Question

This is a MSDN question asked by moondaddy, the source is TextBox. GetLineIndexFromCharacterIndex returns -1 when passing in large text.

The sample code below calls the GetLineIndexFromCharacterIndex method on the TextBox and it returns -1 when passing in text 55,000 or larger. Is this a bug and is there a work-around for this?

public MainWindow()
{
    InitializeComponent();
    string text = "";
    string path = "problematicFile.txt";

    // This text is added only once to the file.
    if (File.Exists(path))
    { 
        text = System.IO.File.ReadAllText(path);
    }            
    textBox.Text = text;
    var chararcter1 = textBox.Text[56218];
    var chararcter2 = textBox.Text[56325];
    int index1 = textBox.GetLineIndexFromCharacterIndex(56218);
    int index2 = textBox.GetLineIndexFromCharacterIndex(56325);
}

Answer 1

Hi,

Welcome to our Microsoft Q&A platform!

The reply form Kareninstructor

There may be, have not tried stuffing that many lines into a TextBox, you could try the following extension method, place into a static class in your project to see if that works.

Taken from https://stackoverflow.com/questions/15204830/get-index-of-line-from-textbox-c-sharp

public static int GetLineIndex(this TextBox textbox, int line)
{
    var text = textbox.Text;
    var thisLine = 0;
    for (var i = 0; i < text.Length; i++)
    {
        if (thisLine == line)
            return i;

        if (text[i] == '\n')
            ++thisLine;
    }

    throw new ArgumentOutOfRangeException();
}

Or report this to Microsoft via the feedback button in Visual Studio.

Since this is WPF your post is being moved to the WPF forum.

Thanks.