Slow performances with QPlainTextEdit

**nekkro-kvlt** · 17th February 2012, 20:34

Hello All,

I'm trying to make a custom TextEditor with some cool features, but I have a show stopper here its the perf of this widget...
I'm drag and dropping a 200Kb text file, and it takes approx 5s to load, where it's near to instantly on most of other standard text editor...

I'm filling the widget like this:

Qt Code:

Switch view

void logEditor::dropEvent(QDropEvent *de)
{
    // Unpack dropped data and handle it the way you want
    const QMimeData* mimeData = de->mimeData();
 
       // check for our needed mime type, here a file or a list of files
       if (mimeData->hasUrls())
       {
           QList<QUrl> urlList = mimeData->urls();
           // extract the local paths of the files
           for (int i = 0; i < urlList.size(); ++i)
           {
               QFile file(urlList.at(i).toLocalFile());
               if (!file.open (QIODevice::ReadOnly))
                    return;
 
               QTextStream stream ( &file );
               //QString line;
               setIsUpdating();
               while( !stream.atEnd() ) {
                    //line = stream.readLine();
                    this->appendPlainText(stream.readLine());
               }
               file.close(); // when your done.
               setIsUpdating(false);
           }
 
       }
}

void logEditor::dropEvent(QDropEvent *de)
{
    // Unpack dropped data and handle it the way you want
    const QMimeData* mimeData = de->mimeData();

       // check for our needed mime type, here a file or a list of files
       if (mimeData->hasUrls())
       {
           QList<QUrl> urlList = mimeData->urls();
           // extract the local paths of the files
           for (int i = 0; i < urlList.size(); ++i)
           {
               QFile file(urlList.at(i).toLocalFile());
               if (!file.open (QIODevice::ReadOnly))
                    return;

               QTextStream stream ( &file );
               //QString line;
               setIsUpdating();
               while( !stream.atEnd() ) {
                    //line = stream.readLine();
                    this->appendPlainText(stream.readLine());
               }
               file.close(); // when your done.
               setIsUpdating(false);
           }

       }
}

To copy to clipboard, switch view to plain text mode

I have also customized a few things, but I therefore disabling all painting events while i'm filling the text, with the setIsUpdating function.
I also even disabled all the fancy stuff to only have a QPlainTextEdit sublass with the drag and drop event and I still have this slowness.

Full code of the editor can be seen here: http://pastebin.com/1jGtFTX8

I don't really know why is it so slow :/

Any ideas ?

**norobro** · 17th February 2012, 21:40

You might try using QTextStream::readAll(). Heed the warning though.

On my machine loading a 362 KB file from disk into a QPlainTextEdit took just over 1 second using readLine() and 40 ms using readAll().

**Lykurg** · 17th February 2012, 21:55

And instead of using setIsUpdating() you could simply use QObject::blockSignals(). That has nothing to do with your original problem, just a side note.

**nekkro-kvlt** · 17th February 2012, 23:11

I'm doing like this now:
this->appendPlainText(stream.readAll());
and it works way better

Also, for the blockSignals, this is good to now, but I think I'll remove the isEditing function... It's been years the last time I've made C++/Qt now, so I kind of forgot the few I knew

Thanks dudes !