Livereload for development purposes: after save the application should reload the GUI entirely.
But there are some C++ objects (used in QML code) that should stay and find themselves in the new version of the GUI.
Possible approach is to add to such object a string property that will be the same in the newely-loaded QML code, so it'll attach to that. Obviously, the object has two parts: the QObject and Qt-independent implementation.
There is a problem with that: the other bindings need such object to be already attached. These signals/properties mustn't arrive earlier.
I'm thinking about setting that 'persist' property in the Component.onCompleted, so it'll be like atomic with the C++ constructor. Will it work? Other suggestions? How do you do it?
Related
I'm modifying a code written in c++ in order to add several features required by my company. I need to modify as less as possible this code, because it's a public code get from a Git repository, and we want to avoid to deviate from the original source code in case we need to synchronize our code with possible new versions in the future.
In this code, a structure is initialized with a call to std::memset. And I had need to add a shared pointer to this structure.
I notice no issue about that, the code compiles, links and works as expected, and I get even no warnings while the compilation.
But is it safe to achieve that this way? May a std::shared_ptr be correctly initialized if it is part of a structure initialized with std::memset? Or are side effects or hazardous issues which prevent to do that?
VS2015 shows how many references there are to a class.
However if the class is started by WebApplication.Run the references are not shown.
The highlighted code does get executed when the application is run.
Is there any way to get the reference count for the Configure method?
Here are two reasons ;)
The Startup Class is invoked by reflection (it does not implement an interface)
I doubt that code pieces outside of your local source code will influence the reference count. So even if somewhere deep in WebApplication.Run the Configure method is invoked (assuming directly over some magic interface), the reference code will not rise. Make sense, otherwise the counter for string would have overflow ;)
I am creating a C++ class that will be registered as a QML type. I want to run some non-trivial logic when the object is initialized. I don't want to put this logic in the constructor because that is bad practice. In a standard C++ class I would usually create a Startup() function with this logic and call it just after initializing the object, but I have no control over this as objects are initialized in QML.
How should I implement this custom initialization logic for a custom QML type?
For those who want the details. I am making a QAbstractListModel that keeps track of all .txt files in a directory. When it is created it will scan the directory (passed in via property) and update its internal collection with the names of all .txt files in that directory.
Edit1: After looking at Qt's example projects I found that many of them actually do all initialization logic in the constructor, including things like setting up DB connections and doing an initial DB query and query parsing. One need only search for "database" from the Qt Creator Welcom->Examples screen to see these samples. I would appreciate it if someone found and explained a better way.
I have an existing project which uses openglEs library (libGLESv2.lib) on DESKTOP platform.
Now I want to use QT as its user interface by using QGLwidget. However after calling any OpenGL function in QGLwidget::initializeGL function I get Access violation executing location 0x00000000 error at the code below,
void MyGLWidget::initializeGL()
{
if (!context()->create())
throw std::exception("no context :)");
context()->makeCurrent();
glViewport(0, 0, 640, 480);
}
If I also include the library opengl32.lib then glviewport function works but when I hit to glGenFramebuffers then I get the same error.
Could you please let me know how can I configure my project to use QT with opengles on desktop platform.
If I also include the library opengl32.lib then glviewport function works but when I hit to glGenFramebuffers then I get the same error.
glViewport is a OpenGL function found in every OpenGL version and profile since version 1. As such it's immediately available simply by linking against the basic OpenGL interface library.
glGenFramebuffers is a function introduced only with OpenGL-3 (OpenGL-ES 2, BTW, OpenGL-ES is not natively supported on Windows) and before you can use it, you have to
check that it is actually supported
load the OpenGL context dependent function pointer at runtime into the variable symbol you're actually calling
Failing to do the second step will give you the error you encounter. Failing to do the first step you try to load it, but loading may fail leading to the same result as if you didn't do (2) at all.
Qt provides all the function loading checks and executions for you, so I suggest you use it: http://doc.qt.io/qt-4.8/qglfunctions.html
It's not perfect, but it gets the job done.
Update (from comments)
Most likely you already have some OpenGL loader library in your project, that actually resolves everything, but before using Qt you did properly initialize it. Now using Qt you've got a mix of statically resolved symbols through opengl32.lib and symbols provided by that loader, yet the loader is not initialized. Look through the code as it was before integrating Qt and look for some initializing call (called after creating the OpenGL context/window but before doing any OpenGL work).
My best guest would be, that the EGL bindings you use also implement the OpenGL-ES wrapper/loader. As I already explained, Windows doesn't natively support OpenGL-ES (only regular OpenGL) and some kind of compatibility layer is required. It is most likely this layer that's getting in your way now. The good news is, that since you're on Windows you can use regular native OpenGL-3 instead; for the most part OpenGL-ES is a subset of OpenGL-3. You'll still need to runtime load GL-3 functions, but as already said, Qt can do that for you.
What to do:
Replace all occurrences of #include <EGL/egl.h> with #include <GL/gl.h> – that should get rid of the symbol shadowing.
Next, for all classes in which use of OpenGL functions is made, add an inheritance of QGLFunctions so that in the classes' namespaces the dynamically loaded functions are used.
Note that every class that inherits QGLFunctions must be instanced only when the target OpenGL context is made current OR you call initializeFunctions on the instances from QGLWidget::initializeGL (or its derivatives). you have to do the function initialization once for each instance of the class inheriting QGLFunctions and the initialization function must be called when the OpenGL context that's to be used is currently active. Like I said, Qt's QGLFunctions is not perfect; if it were it would do the necessary function pointer loading on demand, cache the result and in case of a OpenGL context switch automatically reinitialize.
I'm implementing a drag and drop interface with Qt across X11 and Windows. The interface handles events such that it is not illegal for a user to drop a dragged object on an area which can't handle drops.
In this case, Qt::IgnoreAction should therefore not be treated as an incorrect potential action. To communicate this fact to the user I need a way to stop Qt::ForbiddenCursor from displaying if the current Qt::DropAction is Qt::IgnoreAction.
There are three ways I can see to achieve this (in order of preference):
To override the QCursor used for a drag with Qt::IgnoreAction to something other than Qt::ForbiddenCursor.
To override the bitmap used for Qt::ForbiddenCursor. This is pretty dirty but would be an acceptable solution as long as I don't have to delve into OS-specific configuration.
To override the call made by Qt when a drag leaves a valid drop area (I assume that Qt does the equivalent of QDropEvent::setDropAction(Qt::IgnoreAction) in this case).
Could anyone suggest ways to acheive any of the above?
Note: I have also attempted to use QApplication::setOverrideCursor() just before calling QDrag::exec(). This doesn't seem to have any effect.
Check if QDragEnterEvent comes to application itself (install event filter on QApplication object). If it does, simply accept it and cursor will appear normal.