Delete Lines From Beginning of Multiline Textbox in C#

Question

Is there a graceful way in C# to delete multiple lines of text from the beginning of a multiline textbox? I am using Microsoft Visual C# 2008 Express Edition.

EDIT - Additional Details The multiline textbox in my application is disabled (i.e. it is only editable by the application itself), and every line is terminated with a "\r\n".

Answer 1

This is an incomplete question. So assuming you are using either TextBox or RichTextBox you can use the Lines property found inTextBoxBase.

//get all the lines out as an arry
string[] lines = this.textBox.Lines;

You can then work with this array and set it back.

  this.textBox.Lines= newLinesArray;

This might not be the most elegant way, but it will remove the first line. EDIT: you don't need select, just using skip will be fine

    //number of lines to remove from the beginning
    int numOfLines = 30; 
    var lines = this.textBox1.Lines;
    var newLines = lines.Skip(numOfLines);

    this.textBox1.Lines = newLines.ToArray();

Answer 2

This solution works for me in WPF:

while (LogTextBox.LineCount > Constants.LogMaximumLines)
{
    LogTextBox.Text = LogTextBox.Text.Remove(0, LogTextBox.GetLineLength(0));
}

You can replace LogTextBox with the name of your text box, and Constants.LogMaximumLines with the maximum number of lines you would like your text box to have.

Answer 3

Unfortunately, no, there is no "elegant" way to delete lines from the text of a multiline TextBox, regardless of whether you are using ASP.NET, WinForms, or WPF/Silverlight. In every case, you build a string that does not contain the lines you don't want and set the Text property.

WinForms will help you a little bit by pre-splitting the Text value into lines, using the Lines property, but it's not very helpful because it's a string array, and it's not exactly easy to delete an element of an array.

Generally, this algorithm will work for all possible versions of the TextBox class:

var lines = (from item in myTextBox.Text.Split('\n') select item.Trim());
lines = lines.Skip(numLinesToSkip);
myTextBox.Text = string.Join(Environment.Newline, lines.ToArray());

Note: I'm using Environment.Newline specifically for the case of Silverlight on a Unix platform. For all other cases, you're perfectly fine using "\r\n" in the string.Join call.

Also, I do not consider this an elegant solution, even though it's only 3 lines. What it does is the following:

• splits the single string into an array of strings
• iterates over that array and builds a second array that does not include the lines skipped
• joins the array back into a single string.

I do not consider it elegant because it essentially builds two separate arrays, then builds a string from the second array. A more elegant solution would not do this.