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Re: Focus problem [message #57816 is a reply to message #57812]

Sun, 19 December 2021 14:22

Lance
Messages: 656
Registered: March 2007

Contributor

Hi Silvan:

The way I define WhenSuspiciousKey is a typical way to define an Event. First, the Ctrl or its direvative need to provide a chance for the event in a (relevant) overrided virtual function. In my case, I overrided

bool Key(...)

In my MainWindow::Key(...)
I allowed WhenSuspiciousKey be called at certain time. What is WhenSuspiciousKey? I define it as a member variable of MainWindow of type Event<>

By add this member variable to MainWindow, the user of MainWindow can assign a callback to an instance(object) of this type by

MainWindow m;
m<<[]{...};

There is no magic here. C have simlar (but much limited ) mechanism. WhenSuspiciousKey is like a function pointer to which you can assign a callback. In order for this callback to actually be called, some where, you need to check and call it(in our case, it's in the MainWindow::Key(...) virtual function).

Now, Key is a virtual function, you cannot assign a callback to it. On the other hand, an object of MainWindow, m, has a public member variable name WhenSuspciciousKey, which is of type Event<>. You can access this member variable. One way is by something like

m.WhenSuspiciousKey<<[]{};

-----
PS: On a second thought, use C function pointer as example:

void (*WhenWhat)(int);

void func1(int p)
{
   if(WhenWhat)
      WhenWhat(p);
}

void callback(int p)
{
}

WhenWhat=callback; // this is good
// just like
// WhenSuspiciousKey<<[]{};
// is fine
func1=callback; // this won't compile
// just like
// Key<<[]{};
// won't compile.

[Updated on: Sun, 19 December 2021 15:02]

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