C ++：为事件处理程序创建一个匿名类 [英] C++: Create an anonymous class for event handlers

问题描述

免责声明：此说明包含大量Qt详细信息。他们不必回答这个问题，我只是想给你背景。

Disclaimer: This description contains a lot of Qt specifics. They are not necessary to answer the question, I just wanted to give you the background.

我需要对 focusInEvent of a QTextEdit 。
不幸的是，这不是一个信号，这就是为什么我需要子类 QTextEdit 。由于这是我需要的唯一变化，我想使用一个匿名子类

I need to react on the focusInEvent of a QTextEdit. Unfortunately this is not available as a signal, that's why I need to subclass QTextEdit. Since this is the only change I need, I would like to use an anonymous subclass

像这样：

myTextEdit =new QTextEdit(){
            void focusInEvent(){
     //code here
     }
};

这是我将用Java编写的代码，它不能在c ++中编译。
下面的所有代码都在自定义 QWidget 的构造函数中。 QTextEdit 包含在此小部件中，应在其构造函数中初始化。

This is the code I would write in Java, it doesn't compile in c++. All following code is within the constructor of a custom QWidget. The QTextEdit is contained in this widget and should be initialized in its constructor.

奇怪的是，此代码编译：

Strangely this code compiles:

class MyTextEdit:protected QTextEdit{
    void focusInEvent();
};
auto myTextEdit=new MyTextEdit();

但是没有用，因为我不能分配一个 myTextEdit * 指向 QTextEdit 的指针。不知何故多态性失败。这段代码不编译：

but is useless, since I can't assign an instance of myTextEdit* to a pointer to QTextEdit. Somehow polymorphism fails. This code doesn't compile:

class MyTextEdit:protected QTextEdit{
        void focusInEvent();
    };
QTextEdit* myTextEdit=new MyTextEdit();

编译器错误是：

/home/lars/ProgrammierPraktikum/moleculator/implementation/Moleculator/gui_elements/editor.cpp:40：
错误：'QTextEdit'是
的无法访问的基础Editor :: Editor （std :: shared_ptr）:: MyTextEdit'
QTextEdit * myTextEdit = new MyTextEdit（）;

/home/lars/ProgrammierPraktikum/moleculator/implementation/Moleculator/gui_elements/editor.cpp:40: error: 'QTextEdit' is an inaccessible base of 'Editor::Editor(std::shared_ptr)::MyTextEdit' QTextEdit* myTextEdit=new MyTextEdit();

问题：

Actual question:

如何创建一个与其超类指针兼容的匿名子类？

How do I create an anonymous subclass that is compatible to pointers of its superclass ?

推荐答案

您的子类化尝试

class MyTextEdit:protected QTextEdit{
        void focusInEvent();
    };
QTextEdit* myTextEdit=new MyTextEdit();

几乎可以。

只是因为方法受保护并不意味着您应该继承protected。

Just because the method is protected doesn't mean you should inherit with protected.

• 受保护的方法说：这不是我的界面的一部分。没有人，但我应该能够调用这个。我会自己调用这个（作为事件处理的一部分）。


• 继承protected说：没有人应该知道这个继承，它是一个实现细节，可能对扩展我的类有用。

您希望定期公开继承。

You want the regular public inheritance.

class MyTextEdit:public QTextEdit{
        void focusInEvent();
    };
QTextEdit* myTextEdit=new MyTextEdit();

现在你说MyTextEdit是QTextEdit的替代品。
您可能需要添加一个构造函数以将父窗口部件提供给MyTextEdit。

Now you are saying that MyTextEdit is a replacement for a QTextEdit. You might want to add a constructor to supply the parent widget to MyTextEdit.

在c ++中没有类似java的匿名内部类。

There is no such thing as a java-like anonymous inner class in c++.

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