How to display a text on a RichTextBox char by char?

Question

I have Form1, RichTextBox1 and Button1 on my Form

To understand what i'm trying to do; take a look at this link , type in a facebook profile link and click on Hack Account AND SEE THE GREEN TEXT THAT APPEARS

I'm using the code below in C# to achieve what i want to do :

private void button1_Click(object sender, EventArgs e)
    {
        string myStr = "This is a test string to stylize your RichTextBox1";

        foreach (char c in myStr.ToCharArray()) {

            Thread.Sleep(100);
            richTextBox1.AppendText(c.ToString());

        }
    }

But it doesn't work, the text appears in the text box at one time; Not char by char!

Answer 1

The reason your code is showing all the text at once is using Thread.Sleep() keep the main Thread (the UI thread) suspended / sleep mode, so none of the Application message are processed on form & the form paint / drawing event are not doing the job as the UI thread is sleeping/suspended!

---

Solution 1: Use a helper Thread so that Thread.Sleep() dont make ur app go in non-responsive mode

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

    }

    private void button1_Click(object sender, EventArgs e)
    {
        string myStr = "This is a test string to stylize your RichTextBox1";

        ThreadPool.QueueUserWorkItem(ShowTextInInterval, myStr);
    }

    private void ShowTextInInterval(object state)
    {
        string mystr = state as string;
        if (mystr == null)
        {
            return;
        }
        for (int i = 0; i < mystr.Length; i++)
        {
            AppendNewTextToRichTextBox(mystr[i]);
            Thread.Sleep(100);
        }
    }

    private delegate void app_char(char c);
    private void AppendNewTextToRichTextBox(char c)
    {
        if (InvokeRequired)
        {
            Invoke(new app_char(AppendNewTextToRichTextBox), c);
        }
        else
        {
            richTextBox1.AppendText(c.ToString(CultureInfo.InvariantCulture));
        }
    }



}

---

Solution # 2 : Use a timer

public partial class Form1 : Form
{
    private Timer tbTimer = new Timer();
    string myStr = "This is a test string to stylize your RichTextBox1";
    private int charPos = 0;
    public Form1()
    {
        InitializeComponent();
        tbTimer.Interval = 100;
        tbTimer.Tick += TbTimerOnTick;

    }

    private void TbTimerOnTick(object sender, EventArgs eventArgs)
    {
        if (charPos < myStr.Length - 1)
        {
            richTextBox1.AppendText(myStr[charPos++].ToString(CultureInfo.InvariantCulture));
        }
        else
        {
            tbTimer.Enabled = false;
        }
    }

    private void button1_Click(object sender, EventArgs e)
    {
        tbTimer.Enabled = true;
    }




}

Answer 2

This is because the textbox is not refreshing whilst you are still running your code. Try putting this:

            foreach (char c in myStr.ToCharArray()) {

            Thread.Sleep(100);
            richTextBox1.AppendText(c.ToString());

richTextBox1.Refresh();
        }

Answer 3

The problem you are having is not in appending the text,

richTextBox1.AppendText(c.ToString()); //Good

works as expected but the issue is that you are putting the UI thread to sleep blocking the drawing of the text on the Rich Text Box.

Thread.Sleep(100); //Not so good

A quick workaround would be to add

richTextBox1.Refresh();

This forces the control to be redrawn after appending the text, but note your entire UI is still going to be frozen while the thread sleeping. A better solution maybe to use a System.Windows.Forms.Timer to accomplish your goal. This class triggers an event every specified interval. Some quick code,

    private System.Windows.Forms.Timer TextUpdateTimer = new System.Windows.Forms.Timer();
    private string MyString = "This is a test string to stylize your RichTextBox1";
    private int TextUpdateCount = 0;

    private void button1_Click(object sender, EventArgs e)
    {
        //Sets the interval for firing the "Timer.Tick" Event
        TextUpdateTimer.Interval = 100;
        TextUpdateTimer.Tick += new EventHandler(TextUpdateTimer_Tick);
        TextUpdateCount = 0;
        TextUpdateTimer.Start();
    }

    private void TextUpdateTimer_Tick(object sender, EventArgs e)
    {
        //Stop timer if reached the end of the string
        if(TextUpdateCount == MyString.Length) {
            TextUpdateTimer.Stop();
            return;
        }
        //AppendText method should work as expected
        richTextBox1.AppendText(MyString[TextUpdateCount].ToString());
        TextUpdateCount++;
    }

This updates the text box char by char without blocking the main thread and maintains usability on the front end.