为什么QTextBrowser中的文本不能一一显示，而是一次全部显示？

Question

The snippet I've used is as follows

QDirIterator it(dir, filters, QDir::NoDotAndDotDot | QDir::AllEntries , QDirIterator::Subdirectories | QDirIterator::FollowSymlinks);
    while(it.hasNext())
    {
        it.next();
        if(QFileInfo(it.filePath()).isFile())
        {
            QString name=it.fileName();
            ui->textBrowser_filename->append(name);
        }
    }

It goes through all directories and rather than displaying the filename one-by-one, as I said, it displays the contents of textBrowser all-at-once. What's wrong is happening?

Answer 1

The problem is that you're in a tight loop ( while(it.hasNext()) ), and Qt won't be able to render anything you've asked it to until you exit that loop and control of the UI thread returns to the Qt event loop.

You might be able to get it to render on each loop using QCoreApplication::processEvents , but depending on how many files you add to your text browser, it may become sluggish

QDirIterator it(dir, filters, QDir::NoDotAndDotDot | QDir::AllEntries , QDirIterator::Subdirectories | QDirIterator::FollowSymlinks);
    while(it.hasNext())
    {
        it.next();
        if(QFileInfo(it.filePath()).isFile())
        {
            QString name=it.fileName();
            ui->textBrowser_filename->append(name);

            QCoreApplication::processEvents(); // this will cause the filename to appear
        }
    }

Answer 2

I agree with the first part of Steve's answer: updates to the GUI are expensive and only happen when control returns to the Qt main application event loop.

However, rather than calling processEvents() manually inside the loop (which generally should be avoided), I'd recommend constructing a single string by joining all the filenames you want to add, and then making only a single call to the QTextBrowser::append() function.

Like so:

QStringList list;
while (it.hasNext()) {
    if (QFileInfo(it.filePath()).isFile()) {
        list << it.fileName();
    }
    it.next();
}
ui->textBrowser_filename->append(list.join('\n'));

If this really takes a long time, as it might if you have many hundreds or thousands of files, you can run the code segment that creates the string list inside a background thread (using QThreadPool , QRunnable , QtConcurrent , etc.), and when that is finished, update the text browser with the large string.