TextBox.Text += "string"; vs TextBox.AppendText("string");

Question

what is the difference between these two methods?

Is one more efficient than the other?

I was thinking maybe the AppendText() uses a method similar to the StringBuilder, ie it uses its own cache instead of creating and appending a new string each time, is that true?

Thanks.

Answer 1

As it is clearly mentioned in Remarks section of MSDN Documentation

The AppendText method enables the user to append text to the contents of a text control without using text concatenation, which, can yield better performance when many concatenations are required.

Your question,

what is the difference between these two methods?

We all know how TextBox.Text += something; will work i.e. creating and appending a new string each time but how AppendText works I could not find any code snippet whether internally it uses StringBuilder or something else.

Is one more efficient than the other?

I think answer to above question will depend on the situation, (Based on Test case observation)

if Multiline property is set to false then Concatenation (+=) yields better results but on other hand Multiline property is set to true then AppendText yields far better performance.

EDIT After reading the comment from Rawling I made a custom win-form solution in which I had a simple textbox in which I appended a simple string hello 10000 times using a simple for-loop

    private void btnAppendText_Click(object sender, EventArgs e)
    {
        txtText.Text = string.Empty;
        DateTime startTime = DateTime.Now;
        for (int i = 0; i < 10000; i++)
        {
            txtText.AppendText(s);
        }
        DateTime endTime = DateTime.Now;
        txtTime.Text = (endTime.Ticks - startTime.Ticks).ToString();
    }

    private void btnConcante_Click(object sender, EventArgs e)
    {
        txtText.Text = string.Empty;
        DateTime startTime = DateTime.Now;
        for (int i = 0; i < 5000; i++)
        {
            txtText.Text += s;
        }
        DateTime endTime = DateTime.Now;
        txtTime.Text = (endTime.Ticks - startTime.Ticks).ToString();
    }

Output were very surprising,
TEST 1: Multiline property is true I had to reduce the iteration to half i.e. 5000 for text concatenation as it was taking a very long time.

btnAppendText_Click output on txtTime was 37222129 almost 3-4 seconds for 10000 iteration
btnConcante_Click output on txtTime was 14449906487 more than 25 minutes for only 5000 iterations.

From the above result it is really clear that, AppendText is much faster and more efficient (when Multiline is true) than Concatenation

TEST 2: Multiline property is false

btnConcante_Click output on txtTime was 39862280 almost 3-4 seconds for 10000 iteration
btnAppendText_Click output on txtTime was 1043279672 almost 2-3 minutes for 10000 iteration

From the above result it is really clear that, Concatenation is faster and more efficient (when Multiline is false) than AppendText

Answer 2

The AppendText has nothing to do with StringBuilder. The Text method actually seems simpler (an possibly more performant). See source code of those two methods for reference:

public void AppendText(string text)
{
    if (text.Length > 0)
    {
        int start;
        int length;
        this.GetSelectionStartAndLength(out start, out length);
        try
        {
            int endPosition = this.GetEndPosition();
            this.SelectInternal(endPosition, endPosition, endPosition);
            this.SelectedText = text;
        }
        finally
        {
            if (base.Width == 0 || base.Height == 0)
            {
                this.Select(start, length);
            }
        }
    }
}


public override string Text {
  get {
    return base.Text;
  }
  set {
    if (value != base.Text) {
      base.Text = value;
      if (base.IsHandleCreated) {
        base.SendMessage(185, 0, 0);
      }
    }
  }
}

Answer 3

As a complement to dbw (and in case someone can find where I've made a mistake), here's my performance test:

private void Form1_Click(object sender, EventArgs e)
{
    Stopwatch sw = new Stopwatch();

    sw.Reset();
    textBox1.Text = "";
    sw.Start();
    for (int i = 0; i < 10000; i++)
    {
        textBox1.Text += s;
    }
    sw.Stop();
    var e1 = sw.Elapsed;

    sw.Reset();
    textBox1.Text = "";
    sw.Start();
    for (int i = 0; i < 10000; i++)
    {
        textBox1.AppendText(s);
    }
    sw.Stop();
    var e2 = sw.Elapsed;
}

I see e1 with about 3 seconds and e2 with about 2 minutes.