At that age, kids may be ready to make their own robots or, for example, an alarm that detects when a pesky younger brother sneaks into their room, said Sheena Vaidyanathan, a computer science teacher and curriculum developer for the K-8 level of the Los Altos School District in California, in Silicon Valley.
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Free, open-source programs such as Arduino , as well as pocket-size computers such as Raspberry Pi, allow kids to simply make their own robots and little devices. They may even be ready, at this point, to tackle rudimentary elements of "real" coding languages such as Python or C, she added. Early exposure to computer science may be particularly useful for girls and those from traditionally underrepresented minorities. In , women earned just 14 percent of computer science CS bachelor's degrees, while underrepresented minorities held less than 20 percent of all CS degrees, according to the National Science Foundation.
For instance, a study conducted by Google found that early exposure to computer science coursework was one factor in whether women stuck with the field in college. Many first-timers in CS get intimidated in their introductory programming classes when they are up against students who have been hacking their school networks or scripting Python for years, Steinglass said. Still, it's not clear that early use of coding apps or toys actually makes kids smarter or even better coders. It would be a mistake for parents to think, "'If I throw every single toy at my kid, they're going to be coding geniuses,'" Vaidyanathan said.
The way they play in the mud and run around and play imagination games is probably just as important.
And while some research suggests that classroom exposure to computer science helps build CS skills later on, there's little scientific evidence that a few hours of after-school tinkering with a coding game has the same effect, Ko said. Most toys are aimed at getting kids addicted to the feeling of creatively solving fun, open-ended problems, she said.
Event processing will continue in the targetThread. To move an object to the main thread, use QApplication::instance to retrieve a pointer to the current application, and then use QApplication::thread to retrieve the thread in which the application lives. For example:. Note that all active timers for the object will be reset. The timers are first stopped in the current thread and restarted with the same interval in the targetThread. As a result, constantly moving an object between threads can postpone timer events indefinitely.
A QEvent::ThreadChange event is sent to this object just before the thread affinity is changed. You can handle this event to perform any special processing. Note that any new events that are posted to this object will be handled in the targetThread. Warning: This function is not thread-safe; the current thread must be same as the current thread affinity. In other words, this function can only "push" an object from the current thread to another thread, it cannot "pull" an object from any arbitrary thread to the current thread.
This signal is emitted after the object's name has been changed. The new object name is passed as objectName. See also setParent and children.
Information about all available properties is provided through the metaObject and dynamicPropertyNames. Since both slots and signals can be used as receivers for signals, and the same connections can be made many times, the number of receivers is the same as the number of connections made from this signal. Removes an event filter object obj from this object. The request is ignored if such an event filter has not been installed.
It is always safe to remove an event filter, even during event filter activation i. See also installEventFilter , eventFilter , and event. Returns a pointer to the object that sent the signal, if called in a slot activated by a signal; otherwise it returns 0. The pointer is valid only during the execution of the slot that calls this function from this object's thread context.
The pointer returned by this function becomes invalid if the sender is destroyed, or if the slot is disconnected from the sender's signal. However, getting access to the sender might be useful when many signals are connected to a single slot. Warning: As mentioned above, the return value of this function is not valid when the slot is called via a Qt::DirectConnection from a thread different from this object's thread.
Do not use this function in this type of scenario. Returns the meta-method index of the signal that called the currently executing slot, which is a member of the class returned by sender. If called outside of a slot activated by a signal, -1 is returned. For signals with default parameters, this function will always return the index with all parameters, regardless of which was used with connect.
This does not apply when overloading signals with different parameters. However, getting access to the signal index might be useful when many signals are connected to a single slot. Warning: The return value of this function is not valid when the slot is called via a Qt::DirectConnection from a thread different from this object's thread. See also parent and children. Dynamic properties can be queried again using property and can be removed by setting the property value to an invalid QVariant.
Changing the value of a dynamic property causes a QDynamicPropertyChangeEvent to be sent to the object. See also blockSignals and QSignalBlocker. A timer event will occur every interval milliseconds until killTimer is called. If interval is 0, then the timer event occurs once every time there are no more window system events to process. The virtual timerEvent function is called with the QTimerEvent event parameter class when a timer event occurs.
Reimplement this function to get timer events. If multiple timers are running, the QTimerEvent::timerId can be used to find out which timer was activated. Note that QTimer 's accuracy depends on the underlying operating system and hardware. The timerType argument allows you to customize the accuracy of the timer. See Qt::TimerType for information on the different timer types. Most platforms support an accuracy of 20 milliseconds; some provide more.
If Qt is unable to deliver the requested number of timer events, it will silently discard some. The QTimer class provides a high-level programming interface with single-shot timers and timer signals instead of events. A timer event will occur every time interval until killTimer is called. If time is equal to std::chrono::duration::zero , then the timer event occurs once every time there are no more window system events to process. QTimer provides a higher-level interface to the timer functionality, and also more general information about timers. The timer event is passed in the event parameter.
See also startTimer , killTimer , and event. Returns a translated version of sourceText , optionally based on a disambiguation string and value of n for strings containing plurals; otherwise returns QString::fromUtf8 sourceText if no appropriate translated string is available. If the same sourceText is used in different roles within the same context, an additional identifying string may be passed in disambiguation 0 by default.
In Qt 4. See Writing Source Code for Translation for a detailed description of Qt's translation mechanisms in general, and the Disambiguation section for information on disambiguation.
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Warning: This method is reentrant only if all translators are installed before calling this method. Installing or removing translators while performing translations is not supported. Doing so will probably result in crashes or other undesirable behavior. If you have a pointer to an object, you can use metaObject to retrieve the meta-object associated with that object. Returns the given object cast to type T if the object is of type T or of a subclass ; otherwise returns 0.
If object is 0 then it will also return 0. Note: This function was provided as a workaround for MSVC 6 which did not support member template functions. It is advised to use the other form in new code. Defining this macro will disable narrowing and floating-point-to-integral conversions between the arguments carried by a signal and the arguments accepted by a slot, when the signal and the slot are connected using the PMF-based syntax.
This macro associates extra information to the class, which is available using QObject::metaObject. Instances of subclasses of QObject should not be thought of as values that can be copied or assigned, but as unique identities.businesspodden.se/marciano-reyes-y-la-cruzada.php
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This means that when you create your own subclass of QObject director or indirect , you should not give it a copy constructor or an assignment operator. However, it may not enough to simply omit them from your class, because, if you mistakenly write some code that requires a copy constructor or an assignment operator it's easy to do , your compiler will thoughtfully create it for you.
You must do more. The curious user will have seen that the Qt classes derived from QObject typically include this macro in a private section:. It declares a copy constructor and an assignment operator in the private section, so that if you use them by mistake, the compiler will report an error. But even this might not catch absolutely every case. You might be tempted to do something like this:. First of all, don't do that. It could generate code using neither the copy constructor nor the assignment operator we made private.
In that case, no error would be reported, but your application would probably crash when you called a member function of w. This macro registers an enum type with the meta-object system. This will enable useful features; for example, if used in a QVariant , you can convert them to strings. Likewise, passing them to QDebug will print out their names. This macro registers a single flags type with the meta-object system.
It is typically used in a class definition to declare that values of a given enum can be used as flags and combined using the bitwise OR operator. For example, in QLibrary , the LoadHints flag is declared in the following way:. This macro tells Qt which interfaces the class implements. This is used when implementing plugins. Apply this macro to declarations of member functions to allow them to be invoked via the meta-object system. The macro is written before the return type, as shown in the following example:. Since normalMethod function is not registered in this way, it cannot be invoked using QMetaObject::invokeMethod.
Note: This macro requires the class to be a subclass of QObject. This macro is used for declaring properties in classes that inherit QObject. Properties behave like class data members, but they have additional features accessible through the Meta-Object System. The property name and type and the READ function are required.
The type can be any type supported by QVariant , or it can be a user-defined type. The attributes default to true except USER , which defaults to false. For more details about how to use this macro, and a more detailed example of its use, see the discussion on Qt's Property System.
Apply this macro to declarations of member functions to tag them with a revision number in the meta-object system. This is useful when using the meta-object system to dynamically expose objects to another API, as you can match the version expected by multiple versions of the other API. Consider the following simplified example:. Using the same Window class as the previous example, the newProperty and newMethod would only be exposed in this code when the expected version is 1 or greater. This tag is not used by the meta-object system itself.
Currently this is only used by the QtQml module. It doesn't matter whether Object is a pointer or not, the macro figures that out by itself. This is an additional macro that allows you to mark a single function as a signal. This is an additional macro that allows you to mark a single function as a slot. Documentation contributions included herein are the copyrights of their respective owners. Qt and respective logos are trademarks of The Qt Company Ltd. All other trademarks are property of their respective owners.
Thread Affinity A QObject instance is said to have a thread affinity , or that it lives in a certain thread. All QObjects must live in the same thread as their parent. Consequently: setParent will fail if the two QObjects involved live in different threads. Lesson D. It would be better if we leave 'parent' and 'child' words for Inheritance; for example in "The complex object is sometimes called the whole, or the parent.
We can call the whole to be the 'Owner' and component to be 'Ownee'. That terminology makes sense for compositions, but not for other types of relationships that are non-owning. Parent-child isn't intended to imply anything about ownership. If I'm understanding your question correctly, no.
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If you don't care about that, then there's no need to overload anything. When defining the specific constructor in the Creature class, is it possible to initialize the parameters to default values like this:.
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I am in doubt about the syntax for initializing the location parameter. If I'm not mistaken location should simply call the default constructor of Point2D if no parameter is specified by the user. References have to reference something. The Creature program doesn't have any setters, so I'm not sure what you're actually trying to ask Regarding the include directives main, is it better practice to explicitly include the child class? It's a good practice to include every header that contains classes that your.
You can even do composition in an abstract class you just won't be able to instantiate that class directly. I think, a good thing to add to these parts of the tutorial are the UML diagrams where the ideas are extracted from. Just to post a picture of the UML diagram used to represent compositions, aggregations, etc. I think the direct connection from modelling a piece of software via UML to the implementation in ANY language, would make more evident the explained here. Ie, aggregations exists even when some lenguages don't use pointers or even references, but there are ways to have the same model of parts.
You haven't answered the question "When should I use a subclass instead of direct implementation of a feature?
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You should generally make a member a class type when the storage or manipulation of that member is non-trivial. For example, if a member needs to represent a point or a fraction, you should use a class, because the storage and manipulation of that data isn't trivial. If you need to store an employee's ID or age, use an int, because that is trivial. Hey Alex, I wrote the above program of creatures and point2d, by creating a Creature header and its cpp and same for Point2D I created both its header and cpp I defined the friend function and set functions in the cpp files.
Not sure. When I put this all in one file, it compiled fine. That suggests to me that maybe you forgot to add Creature. Composition makes programmers less worry about the deletion of the object. In most of the case, this type of relation guarantee the existance of the member in such a way it automatically knows when to birth and to death. What is the difference between a default constructor and a specific one? Why we need two here? What is the meaning of the default constructor? The default constructor gets called whenever you create an object without passing arguments to the constructor. Hello Alex, Hope you are doing well.
I have a question regarding to above given Creature class. My question:. Can we consider internally or separately the relationship between Creature class's object and std::ostream's object std::cout as Dependencies, although you have given as a composition between Creature and Point2D classes? If what I said is correct then it is worth noting that the concepts of composition and dependencies are not mutually exclusive, and can be mixed freely within the same class.
Am I right?. If not, please could you clarify it? Thanks for a great tutorial! It is the most precious one. Yes, I'd say std::cout is a dependency in this case, as the class uses it temporarily. You're correct in that the various relationships aren't exclusive -- a single class might contain an composition element, an association element, and a dependency.