I'm trying to make a program similar to notepad. I want to make it so that when you type in a textbox, an opened curly brace would turn into an opened and a closed curly brace.

I just need the if statement to work properly.

if(textBox1.Text[textBox1.SelectionStart] == '{')
{
  //Removes the last {
  textBoxList.Clear();
  for(int i = 0; i < textBox1.TextLength - 2; i  )
  {
    textBoxList.Add(Convert.ToString(textBox1.Text[i]));
  }
  textBox1.Text = "";
  for(int i = 0; i < textBoxList.Count; i  )
  {
    textBox1.Text  = textBoxList[i];
  }
  //Adds the new curly braces
  textBox1.Text  = indentCurlyBraces;
  //Goes inside the if
  textBox1.SelectionStart = textBox1.TextLength - 2;
  textBox1.ScrollToCaret();
}

This if statement is inside of the textbox changed method.

I have tried using textBox1.SelectionStart, but the program crashes because the index is outside of the textBox1 string[] I also have tried subtracting one, two, adding things to the SelectionStart, but everything is still outside the bounds of the array.

CodePudding user response：

Copy this utility class in your solution:

public class TweakTextBox
{
    private readonly string _addValue;

    private readonly string _findValue;

    private readonly TextBox _textBox;

    private bool enable;

    public TweakTextBox(TextBox t, string findValue, string addValue)
    {
        _textBox = t;
        _findValue = findValue;
        _addValue = addValue;
        _textBox.TextChanged  = TextChanged;
        _textBox.PreviewKeyDown  = PreviewKeyDown;
    }

    private void PreviewKeyDown(object? sender, PreviewKeyDownEventArgs e) // this is required to allow backspacing on "}"
    {
        if (e.KeyCode == Keys.Back)
            enable = false; // disable the tweak in order to get the backspace working
        else
            enable = true; // replace the tweak functionality
    }

    private void TextChanged(object? sender, EventArgs e)
    {
        int index = _textBox.SelectionStart - 1; // find current position before char input = current SelectionStart - 1
        if (index >= 0 && (enable)) // if index is valid
        {
            string p = _textBox.Text[index..(index   1)]; // get last input char
            if (p == _findValue) // if found char is the one specified (e.g. "{")
            {
                string pre = _textBox.Text[0..index]; // get all text preceding the found char
                string post = _textBox.Text[(index   1)..]; // get all text following the found char
                _textBox.Text = pre   _findValue   _addValue   post; // final text is = previous text   found char   char to add   following text
                _textBox.Select(index   1, 0); // reposition the caret at the last user's position
            }
        }
    }
}

You just need to create an instance for each TextBox in which you would like to enable that function. Usage example:

public Form1()
{
    InitializeComponent();
    TweakTextBox tweak = new(textBox1, "{", "}"); // add this line in your Form constructor
    // add here other textboxes if you want
}

I added the PreviewKeyDown event, which disables the functionality if backspace is pressed: if you try disabling this event and backspacing with the caret after an automatically added "}" sign, you'll understand why I added this.

I'm sure there are more efficient ways to achive this - probably with WPF I'd use a different approach, but the question is tagged WinForms so I assume you are not using WPF.

Also, I didn't use KeyPress event because text could have changed for other reasons - I really think TextChanged is your desired event.