QPlainTextEdit Set Height Based on Text Pasted In



  • I've derived a class from QPlainTextEdit and connected a slot to the underlying QTextDocument's contentsChanged() signal. What I'm trying to do is auto-size the height of the editor based on the contents. This code accomplishes the auto height...

    @int lineCount = this->document()->lineCount() + 2;
    QFontMetrics fm(this->font());
    int lineSpacing = fm.lineSpacing();
    int height = lineCount * lineSpacing + this->TopMargin() + this->BottomMargin();

    this->setFixedHeight(height);@

    (NOTE: this won't work for QTextEdit, because the lineCount equals the paragraph count, unless you're using a custom layout.)

    The code works great when the user is editing the text. The problems occur when text is pasted in. It seems it takes a while for the lineCount to situate to the contents. If I call this method multiple times within the same signal, the lineCount increases each pass. So it's almost as if the QTextDocument's layout is running in a separate thread which doesn't finish laying out the pasted in text before the contentsChanged signal is generated.

    Any thoughts or suggestions? Is there a better signal to connect to?

    I've looked through the docs and can't find a "finishedLayingOut" signal or something that indicates the lineCount is completely updated.



  • I think I found a suitable solution. I just overrode the paintEvent() and calculated the height there. Seems to work great.


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