How to change current line format in QTextEdit?

[FinderCheng]

Here is what did:

QTextCursor cursor = this->textCursor();
QTextBlockFormat blockFmt;
blockFmt.setNonBreakableLines(true);
blockFmt.setPageBreakPolicy(QTextFormat::PageBreak_AlwaysBefore);
QTextCharFormat charFmt;
charFmt.setFont(data->visualFont());
if(!cursor.hasSelection()) {
    cursor.beginEditBlock();
    cursor.setBlockFormat(blockFmt);
    cursor.mergeBlockCharFormat(charFmt);
    QTextBlock block = cursor.block();
    block.setUserData(data);
    cursor.endEditBlock();
}

QTextCursor cursor = this->textCursor();
QTextBlockFormat blockFmt;
blockFmt.setNonBreakableLines(true);
blockFmt.setPageBreakPolicy(QTextFormat::PageBreak_AlwaysBefore);
QTextCharFormat charFmt;
charFmt.setFont(data->visualFont());
if(!cursor.hasSelection()) {
    cursor.beginEditBlock();
    cursor.setBlockFormat(blockFmt);
    cursor.mergeBlockCharFormat(charFmt);
    QTextBlock block = cursor.block();
    block.setUserData(data);
    cursor.endEditBlock();
}

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What I want to do is: change current line's format if there is no selection. So if cursor.hasSelection() is false, I just merge new format to block chars. But this does not work.