Is there an equivalent technique in Cocoa for the synchronous TrackPopupMenu in Windows?

Question

In response to a rightMouse event I want to call a function that displays a context menu, runs it, and responds to the selected menu item. In Windows I can use TrackPopupMenu with the TPM_RETURNCMD flag.

What is the easiest way to implement this in Cocoa? It seems NSMenu:popUpContextMenu wants to post an event to the specified NSView. Must I create a dummy view and wait for the event before returning? If so, how do I "wait" or flush events given I am not returning to my main ?

Answer 1

The 'proper' way to do this in Cocoa is to have your menu item's target and action perform the required method. However, if you must do it within your initial call, you can use [NSView nextEventMatchingMask:] to continually fetch new events that interest you, handle them, and loop. Here's an example which just waits until the right mouse button is released. You'll probably want to use a more complex mask argument, and continually call [NSView nextEventMatchingMask:] until you get what you want.

NSEvent *localEvent = [[self window] nextEventMatchingMask: NSRightMouseUpMask];

I think you'll find the 'proper' way to go much easier.

Answer 2

There is no direct equivalent, except in Carbon, which is deprecated.

For detecting the right-click, follow these instructions. They ensure that you will properly detect right-clicks and right-holds and display the menu when you should and not display it when you shouldn't.

For following events, you might try [[NSRunLoop currentRunLoop] runMode:NSEventTrackingRunLoopMode untilDate:[NSDate distantFuture]]. You will need to call this repeatedly until the user has chosen one of the menu items.

Using nextEventMatchingMask:NSRightMouseUpMask will not work in all, or even most, cases. If the user right-clicks on your control, the right mouse button will go up immediately after it goes down, without selecting a menu item, and the menu item selection will probably (though not necessarily) happen through the left mouse button. Better to just run the run loop repeatedly until the user either selects something or dismisses the menu.

I don't know how to tell that the user has dismissed the menu without selecting anything.

Answer 3

It appears that popUpContextMenu is already synchronous. Since I didn't see a way to use NSMenu without having it send a notification to an NSView I came up with a scheme that instantiates a temporary NSView. The goal is to display a popup menu and return the selected item in the context of a single function call. Following is code snippets of my proposed solution:

// Dummy View class used to receive Menu Events

@interface DVFBaseView : NSView
{
    NSMenuItem* nsMenuItem;
}
- (void) OnMenuSelection:(id)sender;
- (NSMenuItem*)MenuItem;
@end

@implementation DVFBaseView
- (NSMenuItem*)MenuItem
{
    return nsMenuItem;
}

- (void)OnMenuSelection:(id)sender
{
    nsMenuItem = sender;
}

@end

// Calling Code (in response to rightMouseDown event in my main NSView

void HandleRButtonDown (NSPoint pt)
{
    NSRect    graphicsRect;  // contains an origin, width, height
    graphicsRect = NSMakeRect(200, 200, 50, 100);

    //-----------------------------
    // Create Menu and Dummy View
    //-----------------------------

    nsMenu = [[[NSMenu alloc] initWithTitle:@"Contextual Menu"] autorelease];
    nsView = [[[DVFBaseView alloc] initWithFrame:graphicsRect] autorelease];

    NSMenuItem* item = [nsMenu addItemWithTitle:@"Menu Item# 1" action:@selector(OnMenuSelection:) keyEquivalent:@""];

    [item setTag:ID_FIRST];

    item = [nsMenu addItemWithTitle:@"Menu Item #2" action:@selector(OnMenuSelection:) keyEquivalent:@""];

    [item setTag:ID_SECOND];
    //---------------------------------------------------------------------------------------------
// Providing a valid windowNumber is key in getting the Menu to display in the proper location
//---------------------------------------------------------------------------------------------

    int windowNumber = [(NSWindow*)myWindow windowNumber];
    NSRect frame = [(NSWindow*)myWindow frame];
    NSPoint wp = {pt.x, frame.size.height - pt.y};  // Origin in lower left

    NSEvent* event = [NSEvent otherEventWithType:NSApplicationDefined
                     location:wp
                     modifierFlags:NSApplicationDefined 
                     timestamp: (NSTimeInterval) 0
                     windowNumber: windowNumber
                     context: [NSGraphicsContext currentContext]
                     subtype:0
                     data1: 0
                     data2: 0]; 

    [NSMenu popUpContextMenu:nsMenu withEvent:event forView:nsView];      
    NSMenuItem* MenuItem = [nsView MenuItem];

    switch ([MenuItem tag])
    {
    case ID_FIRST: HandleFirstCommand(); break;
    case ID_SECOND: HandleSecondCommand(); break;
    }
 }