QT QSyntaxHighlighter - 什么是setCurrentBlockState角色？

Question

Maybe I'm simply dumb, but I've read the documentation of the qt richtext demo here ( https://doc.qt.io/archives/qt-4.7/richtext-syntaxhighlighter.html ) and the setCurrentBlockState documentation here ( https://doc.qt.io/archives/qt-4.7/qsyntaxhighlighter.html#setCurrentBlockState ) but I still can't figure out what's the meaning how the "newState" and how these functions are used in the "highlightBlock" event.

Can someone enlighten me with simple words please?

Answer 1

As far as Qt is concerned, newState has no meaning; it is an arbitrary integer. When you call setCurrentBlockState , QSyntaxHighlighter will merely associate the newState integer with the current block of text that you are working with inside the highlightBlock member function. In other words, the integer is strictly a user value that you can use to mean anything you want.

As mentioned in the example you posted, the problem with highlightBlock is that it only really knows about the current block of text that the rich text engine has passed into it. If you need to know something about the previous block of text that you processed, you need to store this information somewhere. As such, the setCurrentBlockState function was added such that you could store some arbitrary information about the current block of text that you are working with such that a later invocation of highlightBlock could see what the previous invocation was doing. In the example, it was mentioned that highlighting a multi-line C++ comment would require functionality like this to work properly.

All of that being said, you don't actually have to use setCurrentBlockState . You can implement your own means of storing state between highlightBlock invocations. However, setCurrentBlockState provides an efficient means of associating an integer with a block of text.

Hopefully this makes things clear.

Answer 2

I think I have come to realize that using setCurrentBlockState() to remember the multiline highlighting state will not be sufficient in case you have multiple rules for multiline highlightning. Let's say you have some kind of file where you have different kinds of multiline statement and need to color those differently. Then you need to maintain a current and previous state for each of them. It wasn't enough that I let the multiline's rule index (+1) represent the current highlighting state and then match that index when called for the next block. In that case, one has to maintain the state information for each and every multiline rule.