What's wrong with QTextLayout ?!

[Cortex]

Hi,
My QTextDocument is full of text.
However, when I run this code QTextLayout::lineCount() return always 0.

QTextBlock block = document->begin();
     while(block.isValid()) 
     {
        QTextLayout *layout= block.layout();
        int nbL=layout->lineCount();
        qDebug( "count lines = %i", nbL );
     }

QTextBlock block = document->begin();
     while(block.isValid()) 
     {
        QTextLayout *layout= block.layout();
        int nbL=layout->lineCount();
        qDebug( "count lines = %i", nbL );
     }

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Am I missing something?
What's wrong with it?

Plz help me guys, thanks.