Question

I have to add line numbering to my application (C++/CLI – .net2.0) which is a code editor for specialized programming language.

The problem is in a performance of my solution. I did it like this, for every textChanged event of my _rtbCode control this function is fired:

void DocumentElement::SetupLineNumbersCount() {
    StringBuilder ^builder = gcnew StringBuilder();
    if(_tbLineNumbers->Lines->Length > _rtbCode->Lines->Length) {
        for(int i = 0; i <= _rtbCode->Lines->Length;) {
            if(i != 0) builder->Append("\r\n");
            builder->Append(++ i);
            builder->Append(".");
        }
        _tbLineNumbers->Text = builder->ToString();
    }
    else if(_tbLineNumbers->Lines->Length < _rtbCode->Lines->Length) {
        builder->Append(_tbLineNumbers->Text);
        for(int i = _tbLineNumbers->Lines->Length; i < _rtbCode->Lines->Length;) {
            builder->Append("\r\n");
            builder->Append(++ i);
            builder->Append(".");
        }
        _tbLineNumbers->Text = builder->ToString();
    }
}

Where _tbLineNumbers is a TextBox where line numbers are put.
This is soooo slow (I’ve compared this with some other code editors). I tried to paste couple lines (around 10000) and I have huge delay of reaction.

(I already checked How to print line numbers for textbox in c#)

Answer 1

Would it be better to update the line number TextBox on Scroll/Resize events of the code TextBox?

This way, you’d only need to care about the visible set of lines, and typing in the code window wouldn’t require a refresh of the line numbers.

GetFirstVisibleLineIndex

GetLastVisibleLineIndex

These may help you out too!