We have QtQuick Compiler, why we need QtQuickControls2?

[jackylau]

We have QtQuick Compiler, so I think that we can compile QtQuickControls to native code. But why the Qt company develop QtQuickControls2 with C++? Is the performance of the compiled QtQuickControls native code poor? Or any others reason?

[sierdzio]

QtQuick Compiler and Controls 2 are two completely separate technologies (which compliment each other). Developing the first does not invalidate the second.

QtQuick Controls 1 have poor performance (not the compiled code - the quick compiler produces good code, it's just that Controls 1 are too complex) and some questionable design choices. Controls 2 are cleaner, much faster, has more components - overall a better option.

As for performance comparison, check out the initial QQC2 blog - http://blog.qt.io/blog/2015/03/31/qt-quick-controls-for-embedded/.

Going back to the quick compiler - don't get mistaken about what it does. It does not magically improve runtime performance. What the compiler (and the newer QML cache) does is to pre-parse the QML code and compile it into a binary representation which can then be quickly loaded into memory. It does improve startup time, but it does not improve runtime performance.