Hello,
could you post some code please ?

Well, how did you get a pointer _textInputPtr on your QML element ?
How did you connect with the Context or with DecalrativeView?

please post the complete code….

textInputPtr is the id of the TextInput from the QML.

I made a c++ item which inherits QWidget and used on QML (i registered it)

You cannot use QML id in C++, that don’t make any sense.
May i ask you what kind of thing you want to achieve with your textInput?
In some case, it is quite simplier to manage things in javascript inside QML, and then send an signal to C++ when needed.

The qML id is a pointer to QObject.
I want to use a c++ virtual keyboard on QML

How about sending a mouse event? e.g. https://gist.github.com/4415306

But I want to send Key event

At least with Qt5, one working solution seemingly is to use receiver->window()->sendEvent(),
as depicted at https://bugreports.qt-project.org/browse/QTBUG-15496 .