How to Display and Manage a Simple Application-Modal Dialog in Cocoa

Question

I am not sure I am doing things the right way, or if I have it all hacked up.

I have a really simple test application (not document-based) I created for learning how to work with application-modal dialogs in Cocoa applications.

With the application project "TestModalDialog", I have a simple MainMenu.xib with the default view and a button, "Show Dialog", I added. I created a second XIB called TheDialog.xib that has "Cancel" and "OK" buttons. That xib has as its owner a class derived from NSWindowController called "TheDialogController"; the window outlet and delegate are connected to the controller.

Selection of "Show Dialog" on the main view will launch the dialog. Selection of "Cancel" or "OK" will dismiss the dialog. Here is the pretty simple code:

//  TestModalDialogAppDelegate.h  
//  TestModalDialog  

#import <Cocoa/Cocoa.h>  

@class TheDialogController;  

@interface TestModalDialogAppDelegate : NSObject <NSApplicationDelegate>  
{  
  NSWindow *window;  
  TheDialogController* theDialogController;  
}  

@property (assign) IBOutlet NSWindow *window;  
- (IBAction)showDialog:(id)sender;  

@end  

//  TestModalDialogAppDelegate.m  
//  TestModalDialog  

#import "TestModalDialogAppDelegate.h"  
#import "TheDialogController.h"  

@implementation TestModalDialogAppDelegate  

@synthesize window;  

- (void)applicationDidFinishLaunching:(NSNotification *)aNotification  
{  
  theDialogController= [[TheDialogController alloc] init];  
}  

- (void)dealloc  
{
  if(nil != theDialogController)   
    [theDialogController release];  

  [super dealloc];  
}  

- (IBAction)showDialog:(id)sender  
{  
  if(nil == theDialogController)  
  {  
    NSAlert* alert= [NSAlert alertWithMessageText:@"Dialog Error" defaultButton:nil alternateButton:nil otherButton:nil informativeTextWithFormat:@"The dialog controller was not allocated."];  
    [alert runModal];  
    return;  
  }

  NSInteger result= [NSApp runModalForWindow:[theDialogController window]]; 
  // Do something with result.... 
}  
@end  

//  TheDialogController.h  
//  TestModalDialog  

#import <Cocoa/Cocoa.h>  

@interface TheDialogController : NSWindowController  
{  
  // BOOL userClickedCloseOrOk; // Removed based on answer.  
  // Should declare a common define - just being lazy.  
  NSInteger userClickedOk;  // Added based on answer.  
  UInt16 timesShown;   
}  

- (IBAction)showWindow:(id)sender;  
- (IBAction)closeDialog:(id)sender;  
- (IBAction)okDialog:(id)sender;  
//- (BOOL)windowShouldClose:(id)sender;   // Removed based on answer.  
- (void)windowWillClose:(NSNotification*)notification;  // Added based on answer.   
- (void)windowDidBecomeKey:(NSNotification*)notification;  // To set title when modal.  
@end  

//  TheDialogController.m  
//  TestModalDialog  

#import "TheDialogController.h"  

@implementation TheDialogController  

- (id)init  
{  
  self = [super initWithWindowNibName:@"TheDialog"];  

  userClickedOk= 0;  // Added based on answer.  
  // userClickedCloseOrOk= FALSE;  // Removed based on answer.  

  return self;  
}  

-(void)dealloc  
{  
  // Do member cleanup if needed.
  [super dealloc];  
}  

- (void)windowDidLoad  
{  
  [super windowDidLoad];  

  // Initialize as needed....  
  [[self window] center];  // Center the window.  
}  

// Does not show with runModalForWindow.  
- (IBAction)showWindow:(id)sender  
{  
  // Just playing with the window title....  
  ++timesShown;  
  NSString* newTitle= [NSString stringWithFormat:@"Shown %d Times", timesShown];  
  [[self window] setTitle:newTitle];  
  return [super showWindow:sender];  
}  

// This method no longer used for this solution based on the answer.  
//- (BOOL)windowShouldClose:(id)sender  
//{  
//  if(!userClickedCloseOrOk)  // The user did not click one of our buttons.  
//    [NSApp abortModal];  
//  else  
//    userClickedCloseOrOk= FALSE;  // Clear for next time.  
//  
//  return TRUE;  
//}  

// Added based on answer.  
- (void)windowWillClose:(NSNotification*)notification  
{  
  [NSApp stopModalWithCode:userClickedOk];  
  userClickedOk= 0;  // Reset for next time.  
}  

// Note - the title will update every time the window becomes key. To do the  
// update only once per modal session, a flag can be added. There might be a better  
// notification to catch.  
- (void)windowDidBecomeKey:(NSNotification*)notification  
{  
  ++timesShown;  
  NSString* newTitle= [NSString stringWithFormat:@"Shown %d Times", timesShown];  
  [[self window] setTitle:newTitle];  
}  

- (IBAction)closeDialog:(id)sender  
{  
  //userClickedCloseOrOk= TRUE;  // Removed based on answer.  
  //[NSApp abortModal];  // Removed based on answer.  
  //[[self window] performClose:self];  // Removed based on answer.  
  [[self window] close];  // Know we want to close - based on answer.  
}  

- (IBAction)okDialog:(id)sender  
{  
  userClickedOk= 1;  // Added based on answer.  
  //userClickedCloseOrOk= TRUE;  // Removed based on answer.  
  //[NSApp stopModal];  // Removed based on answer.  
  //[[self window] performClose:self];  // Removed based on answer.  
  [[self window] close];  // Know we want to close - based on answer.  
}    

@end  

I had trouble with the modality - before I put in userClickedCloseOrOk and tests, if the user hit the close button (upper-left red dot), the dialog would close but the modal session was still running.

I realize I could just leave the close-button off the dialog to start with, but with it there, is what I have demonstrated a good way to catch that scenario, or is there a better way? Or, am I doing something wrong to start with, which creates that problem for me?

Any advice would be appreciated.

NOTE - Code from the original example commented out and replaced with code based on the answer. Also added a new notification handler.

Answer 1

In the okDialog: and closeDialog: methods call close instead of performClose: to avoid the window calling the windowShouldClose: delegate method. That way you don't need userClickedCloseOrOk.

Also I think you want to be calling stopModalWithCode: instead of stopModal since in the app delegate you seem to be interested in the result. And you can call stopModal or stopModalWithCode: instead of abortModal because you are always in the runloop when you call it (abort is for when you are outside of the modal runloop, like in another thread or timer's runloop).

In windowShouldClose: you are doing an action (abortModal) when you should only be answering the question "should this window close". The windowWillClose: delegate method is where you should do actions if you need to.

Sheets are useful when there is one window and it tells the user they can't do anything with it until they complete whatever is in the sheet. Application-modal windows are useful when you have multiple windows that the user can't interact with until they complete whatever is in the modal window or where there is an error that involves the whole application but is not tied to the content of one window. In their HIG Apple suggests avoiding the use of Application-modal windows whenever possible.