C ++子类，继承和铸造 [英] C++ Subclassing, Inheritance and Casting

问题描述

在Qt框架中，有两个类：QTreeWidget和QTreeWidgetitem 。

我已经子类化了一个QTreeWidgetitem：

  
 class MyQTreeWidgetitem：public QObject，public QTreeWidgetitem 
 {
 
 ... 
 
 public：
 int myCustomVariable; 
} 
  

我将此添加到QTreeWidget中，执行的操作如下：

  
 MyQTreeWidgetitem * item = new MyQTreeWidgetitem; 
 item-> myCustomVariable = 10; 
 
 tree-> addTopLevelItem（item）; 
  

现在，如果我需要调用tree-> topLevelItem QTreeWidgetitem *。

然而，我后面是MyQTreeWidgetitem *所以我：

  
 MyQTreeWidgetItem * theitem =（MyQTreeWidgetItem *）tree-> topLevelItem（n）; 
  

这样做的问题是，this-> myCustomVariable不再等于10。

有没有办法保持MyQTreeWidgetitem完好无损？

解决方案

但你可以尝试做一个适当的 dynamic_cast<> ，它将验证对象是否实际上是一个 MyQTreeWidgetItem * 返回0），以及正确执行指针转换（我不知道如果C风格的转换是返回 QObject 的地址。您可以打印出指针，也可以更深入地了解这个问题。

This specific conundrum is hard for me to explain so I'll try as best I can.

In the Qt framework, there are 2 classes: QTreeWidget and QTreeWidgetitem.

I have subclassed a QTreeWidgetitem:

class MyQTreeWidgetitem : public QObject, public QTreeWidgetitem
{

...

public:
  int myCustomVariable;
}

I add this to a QTreeWidget doing something like:

MyQTreeWidgetitem *item = new MyQTreeWidgetitem;
item->myCustomVariable = 10;

tree->addTopLevelItem(item);

Now, if ever I need to call tree->topLevelItem(x), all I get back is the QTreeWidgetitem*.

However, what I'm after is the MyQTreeWidgetitem* so I:

MyQTreeWidgetItem *theitem = (MyQTreeWidgetItem*)tree->topLevelItem(n);

The problem with this is that theitem->myCustomVariable no longer equals 10.

Is there a way to keep MyQTreeWidgetitem intact?

解决方案

I don't know Qq, but you could try doing a proper dynamic_cast<> which will verify whether the object is actually a MyQTreeWidgetItem* (otherwise returns 0), as well as performing the pointer conversion properly (I'm not sure if the C-style cast is returning the address of the QObject). You can print out the pointers and get more insight into this problem too.

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