TextBox.AppendText

TextBox provides the C# AppendText method. This method appends lines of text. With it we have to deal with newlines and avoid extra line breaks.

If we append newlines on each line, there will be an extra blank line at the end of our multiline TextBox. This can be avoided with some custom logic.

AppendText example

We can append text to a TextBox with the method AppendText. But this call will not append a newline to the end—all the text will run together.

private void Test()
{
    for (int i = 0; i < 2; i++)
    {
        textBox1.AppendText("Some text");
    }
}
Some textSome text

Line example

We can append lines by using Environment.NewLine and then adding some conditional logic. Unlike AppendLine, this does not add extra newlines.

public partial class Form1 : Form
{
    private void AppendTextBoxLine(string myStr)
    {
        if (textBox1.Text.Length > 0)
        {
            textBox1.AppendText(Environment.NewLine);
        }
        textBox1.AppendText(myStr);
    }

    private void TestMethod()
    {
        for (int i = 0; i < 2; i++)
        {
            AppendTextBoxLine("Some text");
        }
    }
}
Some text
Some text

Example 3

If we do not check the length of the Text in the TextBox, we will have unwanted line breaks. But Sometimes we may prefer to always append newlines.

public partial class Browser : Form
{
    private void Test()
    {
        // Will leave a blank line on the end.
        for (int i = 0; i < 2; i++)
        {
            textBox1.AppendText("Some text" + Environment.NewLine);
        }

        // Will leave a blank line on the start.
        for (int i = 0; i < 2; i++)
        {
            textBox1.AppendText(Environment.NewLine + "Some text");
        }
    }
}

Discussion

These 2 tables demonstrate what the TextBox contents will look like when there is a newline on the end always, and when there is a newline on the start.

[Some text
 Some text
          ]
[Some text
 Some text]

We appended lines to a TextBox with methods written in C#. These methods work well with events like TextChanged, which together can enhance the usability of the form.