Handling NSMenuDelegate menuWillOpen for changing targets

问题

There are lots of related answers about using menuWillOpen. They all explain that one needs to set the menu's delegate first.

This is easy when I have just one target, like a Preferences window or the main application.

But what if I have a document based app, and I need to have the active document handle menuWillOpen? Then the delegate isn't a constant any more.

What's the proper way to handle this? Do I have to set the delegate to a single object (like the AppDelegate) and then forward the call to the active view controller (but how is that done correctly)? Or is there some other elegant way?

回答1:

I came up with this code which appears to work:

// This is in my AppDelegate class, and the NSMenu's delegate points to it:
- (void)menuWillOpen:(NSMenu *)menu {
    // Forward to active document controller
    NSWindow *mainWindow = [NSApplication sharedApplication].mainWindow;
    NSResponder *r = mainWindow.firstResponder;
    while (r) {
        if ([r respondsToSelector:_cmd]) {
            [(id<NSMenuDelegate>)r menuWillOpen:menu];
            return;
        }
        r = r.nextResponder;
    }
}

It assumes that a controller down the responder chain implements menuWillOpen:

来源：https://stackoverflow.com/questions/55987213/handling-nsmenudelegate-menuwillopen-for-changing-targets