C# – Rich Text box scroll to the bottom when new data is written to it

crichtextboxwinforms

My program calls Java and then redirects stdout to a RichTextBox. My problem is that the vertical scrollbar always stays at the top of the box every time data is written.

Even if you scroll to the bottom, once new data has been written it goes to the top. I would like the opposite.

So when new data is written, it stays at the bottom. How can I do this?

Best Answer

Yes, you can use the ScrollToCaret() method:

// bind this method to its TextChanged event handler:
// richTextBox.TextChanged += richTextBox_TextChanged;
private void richTextBox_TextChanged(object sender, EventArgs e) {
   // set the current caret position to the end
   richTextBox.SelectionStart = richTextBox.Text.Length;
   // scroll it automatically
   richTextBox.ScrollToCaret();
}

Related Solutions

C# – Append text to the beginning in the Rich Text Box

Technically if you're inserting it at the top of the text, you're "inserting" or "prepending", not "appending". ;)

You can use the SelectedText property to insert text at the start of a RichTextBox. I just knocked up a quick demo app to test it out:

    private void button1_Click(object sender, EventArgs e)
    {
        richTextBox1.SelectionStart = 0;
        richTextBox1.SelectionLength = 0;
        richTextBox1.SelectedText = DateTime.Now.ToString();
    }

That inserts the current time at the start of the RichTextBox when button1 is clicked.

C# – How to automatically scroll to the bottom of a multiline text box

At regular intervals, I am adding new lines of text to it. I would like the textbox to automatically scroll to the bottom-most entry (the newest one) whenever a new line is added.

If you use TextBox.AppendText(string text), it will automatically scroll to the end of the newly appended text. It avoids the flickering scrollbar if you're calling it in a loop.

It also happens to be an order of magnitude faster than concatenating onto the .Text property. Though that might depend on how often you're calling it; I was testing with a tight loop.

This will not scroll if it is called before the textbox is shown, or if the textbox is otherwise not visible (e.g. in a different tab of a TabPanel). See TextBox.AppendText() not autoscrolling. This may or may not be important, depending on if you require autoscroll when the user can't see the textbox.

It seems that the alternative method from the other answers also don't work in this case. One way around it is to perform additional scrolling on the VisibleChanged event:

textBox.VisibleChanged += (sender, e) =>
{
    if (textBox.Visible)
    {
        textBox.SelectionStart = textBox.TextLength;
        textBox.ScrollToCaret();
    }
};

Internally, AppendText does something like this:

textBox.Select(textBox.TextLength + 1, 0);
textBox.SelectedText = textToAppend;

But there should be no reason to do it manually.

^{(If you decompile it yourself, you'll see that it uses some possibly more efficient internal methods, and has what seems to be a minor special case.)}

Best Answer

Related Solutions

C# – Append text to the beginning in the Rich Text Box

C# – How to automatically scroll to the bottom of a multiline text box

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