Why does appending to TextBox.Text during a loop take up more memory with each iteration?

Question

Short Question

I have a loop that runs 180,000 times. At the end of each iteration it is supposed to append the results to a TextBox, which is updated real-time.

Using MyTextBox.Text += someValue is causing the application to eat huge amounts of memory, and it runs out of available memory after a few thousand records.

Is there a more efficient way of appending text to a TextBox.Text 180,000 times?

Edit I really don't care about the result of this specific case, however I want to know why this seems to be a memory hog, and if there is a more efficient way to append text to a TextBox.

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Long (Original) Question

I have a small app which reads a list of ID numbers in a CSV file and generates a PDF report for each one. After each pdf file is generated, the ResultsTextBox.Text gets appended with the ID Number of the report that got processed and that it was successfully processed. The process runs on a background thread, so the ResultsTextBox gets updated real-time as items get processed

I am currently running the app against 180,000 ID numbers, however the memory the application is taking up is growing exponentially as time goes by. It starts by around 90K, but by about 3000 records it is taking up roughly 250MB and by 4000 records the application is taking up about 500 MB of memory.

If I comment out the update to the Results TextBox, the memory stays relatively stationary at roughly 90K, so I can assume that writing ResultsText.Text += someValue is what is causing it to eat memory.

My question is, why is this? What is a better way of appending data to a TextBox.Text that doesn't eat memory?

My code looks like this:

try
{
    report.SetParameterValue("Id", id);

    report.ExportToDisk(ExportFormatType.PortableDocFormat,
        string.Format(@"{0}\{1}.pdf", new object[] { outputLocation, id}));

    // ResultsText.Text += string.Format("Exported {0}\r\n", id);
}
catch (Exception ex)
{
    ErrorsText.Text += string.Format("Failed to export {0}: {1}\r\n", 
        new object[] { id, ex.Message });
}

It should also be worth mentioning that the app is a one-time thing and it doesn't matter that it is going to take a few hours (or days :)) to generate all the reports. My main concern is that if it hits the system memory limit, it will stop running.

I'm fine with leaving the line updating the Results TextBox commented out to run this thing, but I would like to know if there is a more memory efficient way of appending data to a TextBox.Text for future projects.

Answer 1

I suspect the reason the memory usage is so large is because textboxes maintain a stack so that the user can undo/redo text. That feature doesn't seem to be required in your case, so try setting IsUndoEnabled to false.

Answer 2

Use TextBox.AppendText(someValue) instead of TextBox.Text += someValue. It's easy to miss since it's on TextBox, not TextBox.Text. Like StringBuilder, this will avoid creating copies of the entire text each time you add something.

It would be interesting to see how this compares to the IsUndoEnabled flag from keyboardP's answer.

Answer 3

Instead of using a text box I would do the following:

1. Open up a text file and stream the errors to a log file just in case.
2. Use a list box control to represent the errors to avoid copying potentially massive strings.

Answer 4

Don't append directly to the text property. Use a StringBuilder for the appending, then when done, set the .text to the finished string from the stringbuilder