I have the following code to load a UIImagePickerController which works fine.
UIImagePickerController *mediaUI = [[UIImagePickerController alloc] init];
mediaUI.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
mediaUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeMovie, nil];
mediaUI.delegate = self;
[controller presentModalViewController: mediaUI animated: YES];
return YES;
I would like to load a modal view with some help information on how to use the UIImagePickerController:
UIStoryboard *storyboard = self.storyboard;
HelpViewController *svc = [storyboard instantiateViewControllerWithIdentifier:#"HelpViewController"];
[self presentViewController:svc animated:YES completion:nil];
How can I display the UIImagePickerController after the user dismisses the HelpViewController view?
Don't be tempted to move directly from HelpViewController to UIImagePickerController, you need to get there via your mainViewController.
Let's put your code into a method...
- (void) presentImagePicker {
UIImagePickerController *mediaUI = [[UIImagePickerController alloc] init];
mediaUI.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
mediaUI.mediaTypes = [[NSArray alloc] initWithObjects: (NSString *) kUTTypeMovie, nil];
mediaUI.delegate = self;
[controller presentModalViewController: mediaUI animated: YES];
return YES;
}
(Note that presentModalViewController:animated is depracated since ~iOS5, and you should really replace it with
[controller presentViewController:mediaUI animated:YES completion:nil];)
Let's call your viewControllers mainVC, helpVC and imageVC. There are two ways you can implement this.
method 1 - performSelector
The quick-and-slightly-dirty solution is to do this in your helpVC's dismiss button method:
- (IBAction)dismissHelpAndPresentImagePicker:(id)sender
{
UIViewController* mainVC = self.presentingViewController;
[mainVC dismissViewControllerAnimated:NO completion:
^{
if ([mainVC respondsToSelector:#selector(presentImagePicker)])
[mainVC performSelector:#selector(presentImagePicker)];
}];
}
It's slightly dirty because you need to ensure that presentImagePicker is implemented in mainVC - the compiler will give you no warnings if it is not. Also you are running a completion block after it's object has been dismissed, so there's no certainty it's going to work (in practice, it does, but still...)
Note that you have to assign the pointer self.presentingViewController's to a local variable (mainVC). That's because when helpVC is dismissed, it's presentingViewController property is reset to nil, so by the time you get to run the completion block you cannot use it. But the local variable mainVC is still valid.
method 2 - protocol/delegate
The clean way to do this is to use a protocol in helpVC to declare a delegate method, and make mainVC the delegate. This way the compiler will keep track of everything and warn you if it is not correctly implemented.
Here are the steps to do that:
In helpVC.h add this protocol above the #interface section:
#protocol helpVCDelegate
- (void) dismissHelpAndPresentImagePicker;
#end
In helpVC.h interface section declare a property for its delegate:
#property (nonatomic, weak) id <helpVCDelegate> delegate;
(the <helpVCDelegate> tells the compiler that the delegate is expected to conform to the protocol, so it will have to implement dismissHelpAndPresentImagePicker)
In helpVC.m your method can now look like this:
- (IBAction)dismissHelpAndPresentImagePicker:(id)sender
{
[self.delegate dismissHelpAndPresentImagePicker];
}
In MainVC, when you create HelpVC (=svc in your code), set MainVC as it's delegate:
HelpViewController *svc = [storyboard instantiateViewControllerWithIdentifier:#"HelpViewController"];
svc.delegate = self;
[self presentViewController:svc animated:YES completion:nil];
And be sure to implement the delegate method dismissHelpAndPresentImagePicker
- (void) dismissHelpAndPresentImagePicker
{
[self dismissViewControllerAnimated:NO completion:^{
[self presentImagePicker];
}];
}
Personally I would always use method 2. But I offered up a that solution earlier today to a similar question, and the questioner seemed to think protocol/delegate was overcomplicated. Maybe my answer just made it seem so, I have tried to simplify it here.
Ok guys, I am fairly new to objective C. I have an app that downloads a list of images from my web server and displays the appropriate ones in a UIImage view with swipe gestures to go forward or backwards for the next/previous pic to be displayed. Current naming format for the pictures is like this:
uploaded_141_admin1.png
uploaded_141_admin2.png
uploaded_141_interior1.png
uploaded_141_interior2.png
uploaded_141_exterior1.png
The current code loads every picture into the view that has 141 in the middle part of the filename (or whatever record the user in on... 141 is variable in this instance, just showing here for an example of the format). The problem is, there seems to be no rhyme or reason as to what order they are displayed in. I would like it to use the last part of the filename to sort alphabetically (or even the whole filename, as it would achieve the same result). In the example above, it would display the downloaded pics in the following order when swiping through the uiimageiew:
uploaded_141_admin1.png
uploaded_141_admin2.png
uploaded_141_exterior1.png
uploaded_141_interior1.png
uploaded_141_interior2.png
I've search and can't find what I am looking for (maybe because I'm using the wrong search criteria). Here is my existing code that downloads and displays the images in the UIImageView. I assume the "sort" code would go in here somewhere:
-(void)downloadPictures:(NSArray *)picPaths {
ELog(#"Downloading pictures: %#",picPaths);
// wait indicator
[[WaitingView sharedInstance] setMessage:LocStr(#"Loading pictures... The more pictures there are, the longer this will take. Please be patient.")];
[[WaitingView sharedInstance] showIndicator:YES];
[[WaitingView sharedInstance] displayOn:[self view]];
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
// queue download operation
NSOperationQueue *queue = [[NSOperationQueue alloc] init];
NSInvocationOperation *downloadOp = [[NSInvocationOperation alloc] initWithTarget:self selector:#selector(downloadOperation:) object:picPaths];
[queue addOperation:downloadOp];
}
-(void)downloadOperation:(NSArray *)picPaths {
NSMutableArray *allPictures = [[NSMutableArray alloc] init];
for(NSString *path in picPaths) {
NSURL *url = [NSURL URLWithString:[NSString stringWithFormat:#"http://%#%#/%#/%#",SERVER_ADDRESS,SERVER_PORT,SERVER_PHOTOS,path]];
NSData *picData = [NSData dataWithContentsOfURL:url];
if(picData!=nil) {
UIImage *img = [UIImage imageWithData:picData];
if(img!=nil) {
[allPictures addObject:img];
} else {
ELog(#"Failed to convert data to image from url %#",url);
}
} else {
ELog(#"Failed to download image from url %#",url);
}
}
[[WaitingView sharedInstance] performSelectorOnMainThread:#selector(remove) withObject:nil waitUntilDone:NO];
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
self.pictures=allPictures;
if([self.pictures count]==0) {
[self performSelectorOnMainThread:#selector(downloadErrorMessage) withObject:nil waitUntilDone:NO];
} else {
self.currentIndex=0;
[self performSelectorOnMainThread:#selector(showPicture) withObject:nil waitUntilDone:NO];
}
}
-(void)downloadErrorMessage {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Oooops!" message:LocStr(#"Pictures download failed") delegate:nil cancelButtonTitle:LocStr(#"Close") otherButtonTitles:nil];
[alert show];
[alert release];
[self goBack];
}
-(void)showPicture {
UIImage *image = [self.pictures objectAtIndex:self.currentIndex];
ELog(#"Now displaying image with index %d: %#",self.currentIndex,image);
self.picture.image=image;
[self.picture setNeedsLayout];
}
In your downloadPictures: method you should sort your picPaths array to be the order you want the images before you start the download operation. You can do this by creating a new sorted array using the NSArray method sortedArrayUsingSelector:. Using caseInsensitiveCompare: as the selector for the sort will order the NSStrings in the array alphabetically.
NSArray *sortedPicPaths = [picPaths sortedArrayUsingSelector:#selector(caseInsensitiveCompare:)];
Then when you init your NSInvocationOperation, pass the sorted array as the object.
I'm trying to write an application that allows the user to drag files from the Finder and drop them onto an NSStatusItem. So far, I've created a custom view that implements the drag and drop interface. When I add this view as a subview of an NSWindow it all works correctly -- the mouse cursor gives appropriate feedback, and when dropped my code gets executed.
However, when I use the same view as an NSStatusItem's view it doesn't behave correctly. The mouse cursor gives appropriate feedback indicating that the file can be dropped, but when I drop the file my drop code never gets executed.
Is there something special I need to do to enable drag and drop with an NSStatusItem?
I finally got around to testing this and it works perfectly, so there's definitely something wrong with your code.
Here's a custom view that allows dragging:
#implementation DragStatusView
- (id)initWithFrame:(NSRect)frame
{
self = [super initWithFrame:frame];
if (self) {
//register for drags
[self registerForDraggedTypes:[NSArray arrayWithObjects: NSFilenamesPboardType, nil]];
}
return self;
}
- (void)drawRect:(NSRect)dirtyRect
{
//the status item will just be a yellow rectangle
[[NSColor yellowColor] set];
NSRectFill([self bounds]);
}
//we want to copy the files
- (NSDragOperation)draggingEntered:(id<NSDraggingInfo>)sender
{
return NSDragOperationCopy;
}
//perform the drag and log the files that are dropped
- (BOOL)performDragOperation:(id <NSDraggingInfo>)sender
{
NSPasteboard *pboard;
NSDragOperation sourceDragMask;
sourceDragMask = [sender draggingSourceOperationMask];
pboard = [sender draggingPasteboard];
if ( [[pboard types] containsObject:NSFilenamesPboardType] ) {
NSArray *files = [pboard propertyListForType:NSFilenamesPboardType];
NSLog(#"Files: %#",files);
}
return YES;
}
#end
Here's how you'd create the status item:
NSStatusItem* item = [[[NSStatusBar systemStatusBar] statusItemWithLength:NSSquareStatusItemLength] retain];
DragStatusView* dragView = [[DragStatusView alloc] initWithFrame:NSMakeRect(0, 0, 24, 24)];
[item setView:dragView];
[dragView release];
Since Yosemite, the method for setting a view on NSStatusItem is deprecated but fortunately there is a much nicer way using the new NSStatusItemButton property on NSStatusItem:
- (void)applicationDidFinishLaunching: (NSNotification *)notification {
NSImage *icon = [NSImage imageNamed:#"iconName"];
//This is the only way to be compatible to all ~30 menu styles (e.g. dark mode) available in Yosemite
[normalImage setTemplate:YES];
statusItem.button.image = normalImage;
// register with an array of types you'd like to accept
[statusItem.button.window registerForDraggedTypes:#[NSFilenamesPboardType]];
statusItem.button.window.delegate = self;
}
- (NSDragOperation)draggingEntered:(id<NSDraggingInfo>)sender {
return NSDragOperationCopy;
}
- (BOOL)performDragOperation:(id<NSDraggingInfo>)sender {
//drag handling logic
}
Please be aware that the button property is only available starting in 10.10 and you might have to keep your old solution if you support 10.9 Mavericks or below.
I'm trying to subclass NSScroller in order to draw my own scroller knob. To do this, I've subclassex NSScrollView and usex the following code to instantiate my custom NSScrollers:
- (void)awakeFromNib;
{
NSRect horizontalScrollerFrame = [[self horizontalScroller] frame];
NSRect verticalScrollerFrame = [[self verticalScroller] frame];
NSString *scrollBarVariant = [[[NSUserDefaults standardUserDefaults] persistentDomainForName:NSGlobalDomain] valueForKey:#"AppleScrollBarVariant"];
if (![scrollBarVariant isEqualToString:#"DoubleBoth"]) {
[self setVerticalScroller:[[[TRScroller alloc] initWithFrame:verticalScrollerFrame] autorelease]];
[self setHorizontalScroller:[[[TRScroller alloc] initWithFrame:horizontalScrollerFrame] autorelease]];
}
}
This works and my NSScrollers display correctly. But I'm occasionally seeing rendering issues upon first loading my application. Within Interface Builder I have laid out a number of NSScrollViews with their scrollbars set to hide automatically. The issue I'm seeing is that when the application first loads, the scrollbar backgrounds are rendered across the NSScrollViews contents.
alt text http://www.freeimagehosting.net/uploads/1d3fc75db8.png
I believe this is because I instantiate my NSScroll subclass (TRSubclass) via awakeFromNib, which means that the scrollbars are given the frame of the NSScrollView before it is automatically resized to meet the windows saved location and size (in other words, it's using the frame that's assigned by default within Interface Builder). What's the best way around this?
I've tried forcing the NSScrollView to redisplay (using setNeedsDisplay: and display:) but with no luck. Has anyone else come across a similar issue?
I'm using the same schema in my applications and I fighted this issues a lot. I use the same trick: scrollers are substituted in [scrollView awakeFromNib] methods, but I don't face such rendering issues at the moment. You can try to play with "draws background" property of the NSScrollView - it really helps sometimes
- (void)changeSubs
{
// change clip view
// ...
// change scrollers
NSRect horizontalScrollerFrame = [[self horizontalScroller] frame];
NSRect verticalScrollerFrame = [[self verticalScroller] frame];
if (![[self verticalScroller] isKindOfClass:[CRScroller class]])
[self setVerticalScroller:[[[CRScroller alloc] initWithFrame:verticalScrollerFrame] autorelease]];
if (![[self horizontalScroller] isKindOfClass:[CRScroller class]])
[self setHorizontalScroller:[[[CRScroller alloc] initWithFrame:horizontalScrollerFrame] autorelease]];
}
- (id)initWithFrame:(NSRect)frame
{
self = [super initWithFrame:frame];
if (self)
{
[self changeSubs];
}
return self;
}
- (id)initWithCoder:(NSCoder *)aDecoder
{
NSKeyedUnarchiver* unpacker = (id)aDecoder;
[unpacker setClass:[CRClipView class] forClassName:[NSClipView className]];
[unpacker setClass:[CRScroller class] forClassName:[NSScroller className]];
self = [super initWithCoder:aDecoder];
if (self)
{
}
return self;
}
- (void)awakeFromNib
{
[self changeSubs];
}
There are few tricks here, they work depending on a way NSScrollView is created. 'isKindOfClass' check helps to avoid double-swap.
When I display an NSAlert like this, I get the response straight away:
int response;
NSAlert *alert = [NSAlert alertWithMessageText:... ...];
response = [alert runModal];
The problem is that this is application-modal and my application is document based. I display the alert in the current document's window by using sheets, like this:
int response;
NSAlert *alert = [NSAlert alertWithMessageText:... ...];
[alert beginSheetModalForWindow:aWindow
modalDelegate:self
didEndSelector:#selector(alertDidEnd:returnCode:contextInfo:)
contextInfo:&response];
//elsewhere
- (void) alertDidEnd:(NSAlert *) alert returnCode:(int) returnCode contextInfo:(int *) contextInfo
{
*contextInfo = returnCode;
}
The only issue with this is that beginSheetModalForWindow: returns straight away so I cannot reliably ask the user a question and wait for a response. This wouldn't be a big deal if I could split the task into two areas but I can't.
I have a loop that processes about 40 different objects (that are in a tree). If one object fails, I want the alert to show and ask the user whether to continue or abort (continue processing at the current branch), but since my application is document based, the Apple Human Interface Guidelines dictate to use sheets when the alert is specific to a document.
How can I display the alert sheet and wait for a response?
We created a category on NSAlert to run alerts synchronously, just like application-modal dialogs:
NSInteger result;
// Run the alert as a sheet on the main window
result = [alert runModalSheet];
// Run the alert as a sheet on some other window
result = [alert runModalSheetForWindow:window];
The code is available via GitHub, and the current version posted below for completeness.
Header file NSAlert+SynchronousSheet.h:
#import <Cocoa/Cocoa.h>
#interface NSAlert (SynchronousSheet)
-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow;
-(NSInteger) runModalSheet;
#end
Implementation file NSAlert+SynchronousSheet.m:
#import "NSAlert+SynchronousSheet.h"
// Private methods -- use prefixes to avoid collisions with Apple's methods
#interface NSAlert ()
-(IBAction) BE_stopSynchronousSheet:(id)sender; // hide sheet & stop modal
-(void) BE_beginSheetModalForWindow:(NSWindow *)aWindow;
#end
#implementation NSAlert (SynchronousSheet)
-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow {
// Set ourselves as the target for button clicks
for (NSButton *button in [self buttons]) {
[button setTarget:self];
[button setAction:#selector(BE_stopSynchronousSheet:)];
}
// Bring up the sheet and wait until stopSynchronousSheet is triggered by a button click
[self performSelectorOnMainThread:#selector(BE_beginSheetModalForWindow:) withObject:aWindow waitUntilDone:YES];
NSInteger modalCode = [NSApp runModalForWindow:[self window]];
// This is called only after stopSynchronousSheet is called (that is,
// one of the buttons is clicked)
[NSApp performSelectorOnMainThread:#selector(endSheet:) withObject:[self window] waitUntilDone:YES];
// Remove the sheet from the screen
[[self window] performSelectorOnMainThread:#selector(orderOut:) withObject:self waitUntilDone:YES];
return modalCode;
}
-(NSInteger) runModalSheet {
return [self runModalSheetForWindow:[NSApp mainWindow]];
}
#pragma mark Private methods
-(IBAction) BE_stopSynchronousSheet:(id)sender {
// See which of the buttons was clicked
NSUInteger clickedButtonIndex = [[self buttons] indexOfObject:sender];
// Be consistent with Apple's documentation (see NSAlert's addButtonWithTitle) so that
// the fourth button is numbered NSAlertThirdButtonReturn + 1, and so on
NSInteger modalCode = 0;
if (clickedButtonIndex == NSAlertFirstButtonReturn)
modalCode = NSAlertFirstButtonReturn;
else if (clickedButtonIndex == NSAlertSecondButtonReturn)
modalCode = NSAlertSecondButtonReturn;
else if (clickedButtonIndex == NSAlertThirdButtonReturn)
modalCode = NSAlertThirdButtonReturn;
else
modalCode = NSAlertThirdButtonReturn + (clickedButtonIndex - 2);
[NSApp stopModalWithCode:modalCode];
}
-(void) BE_beginSheetModalForWindow:(NSWindow *)aWindow {
[self beginSheetModalForWindow:aWindow modalDelegate:nil didEndSelector:nil contextInfo:nil];
}
#end
The solution is to call
[NSApp runModalForWindow:alert];
after beginSheetModalForWindow. Also, you need to implement a delegate that catches the "dialog has closed" action, and calls [NSApp stopModal] in response.
Here is a NSAlert category that solves the issue (as suggested by Philipp with the solution proposed by Frederick and improved by Laurent P.: I use a code block instead of a delegate, so it is simplified once again).
#implementation NSAlert (Cat)
-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow
{
[self beginSheetModalForWindow:aWindow completionHandler:^(NSModalResponse returnCode)
{ [NSApp stopModalWithCode:returnCode]; } ];
NSInteger modalCode = [NSApp runModalForWindow:[self window]];
return modalCode;
}
-(NSInteger) runModalSheet {
return [self runModalSheetForWindow:[NSApp mainWindow]];
}
#end
Just in case anyone comes looking for this (I did), I solved this with the following:
#interface AlertSync: NSObject {
NSInteger returnCode;
}
- (id) initWithAlert: (NSAlert*) alert asSheetForWindow: (NSWindow*) window;
- (NSInteger) run;
#end
#implementation AlertSync
- (id) initWithAlert: (NSAlert*) alert asSheetForWindow: (NSWindow*) window {
self = [super init];
[alert beginSheetModalForWindow: window
modalDelegate: self didEndSelector: #selector(alertDidEnd:returnCode:) contextInfo: NULL];
return self;
}
- (NSInteger) run {
[[NSApplication sharedApplication] run];
return returnCode;
}
- (void) alertDidEnd: (NSAlert*) alert returnCode: (NSInteger) aReturnCode {
returnCode = aReturnCode;
[[NSApplication sharedApplication] stopModal];
}
#end
Then running an NSAlert synchronously is as simple as:
AlertSync* sync = [[AlertSync alloc] initWithAlert: alert asSheetForWindow: window];
int returnCode = [sync run];
[sync release];
Note there is potential for re-entrancy issues as discussed, so be careful if doing this.
Unfortunately, there is not much you can do here. You basically have to make a decision: re-architect your application so that it can process the object in an asynchronous manner or use the non-approved, deprecated architecture of presenting application modal alerts.
Without knowing any information about your actual design and how you processes these objects, it's hard to give any further information. Off the top of my head, though, a couple of thoughts might be:
Process the objects in another thread that communicates with the main thread through some kind of run loop signal or queue. If the window's object tree gets interrupted, it signals the main thread that it was interrupted and waits on a signal from the main thread with information about what to do (continue this branch or abort). The main thread then presents the document-modal window and signals the process thread after the user chooses what to do.
This may be really over-complicated for what you need, however. In that case, my recommendation would be to just go with the deprecated usage, but it really depends on your user requirements.
Swift 5:
extension NSAlert {
/// Runs this alert as a sheet.
/// - Parameter sheetWindow: Parent window for the sheet.
func runSheetModal(for sheetWindow: NSWindow) -> NSApplication.ModalResponse {
beginSheetModal(for: sheetWindow, completionHandler: NSApp.stopModal(withCode:))
return NSApp.runModal(for: sheetWindow)
}
}
here is my answer:
Create a global class variable 'NSInteger alertReturnStatus'
- (void)alertDidEndSheet:(NSWindow *)sheet returnCode:(NSInteger)returnCode contextInfo:(void *)contextInfo
{
[[sheet window] orderOut:self];
// make the returnCode publicly available after closing the sheet
alertReturnStatus = returnCode;
}
- (BOOL)testSomething
{
if(2 != 3) {
// Init the return value
alertReturnStatus = -1;
NSAlert *alert = [[[NSAlert alloc] init] autorelease];
[alert addButtonWithTitle:#"OK"];
[alert addButtonWithTitle:#"Cancel"];
[alert setMessageText:NSLocalizedString(#"Warning", #"warning")];
[alert setInformativeText:#"Press OK for OK"];
[alert setAlertStyle:NSWarningAlertStyle];
[alert setShowsHelp:NO];
[alert setShowsSuppressionButton:NO];
[alert beginSheetModalForWindow:[self window] modalDelegate:self didEndSelector:#selector(alertDidEndSheet:returnCode:contextInfo:) contextInfo:nil];
// wait for the sheet
NSModalSession session = [NSApp beginModalSessionForWindow:[alert window]];
for (;;) {
// alertReturnStatus will be set in alertDidEndSheet:returnCode:contextInfo:
if(alertReturnStatus != -1)
break;
// Execute code on DefaultRunLoop
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate:[NSDate distantFuture]];
// Break the run loop if sheet was closed
if ([NSApp runModalSession:session] != NSRunContinuesResponse
|| ![[alert window] isVisible])
break;
// Execute code on DefaultRunLoop
[[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode
beforeDate:[NSDate distantFuture]];
}
[NSApp endModalSession:session];
[NSApp endSheet:[alert window]];
// Check the returnCode by using the global variable alertReturnStatus
if(alertReturnStatus == NSAlertFirstButtonReturn) {
return YES;
}
return NO;
}
return YES;
}
Hope it'll be of some help,
Cheers
--Hans
This is the version of Laurent, et al., above, translated into Swift 1.2 for Xcode 6.4 (latest working version as of today) and tested in my app. Thanks to all those who contributed to make this work! The standard documentation from Apple gave me no clues as to how go about this, at least not anywhere that I could find.
One mystery remains to me: why I had to use the double exclamation point in the final function. NSApplication.mainWindow is supposed to be just an optional NSWindow (NSWindow?), right? But the compiler gave the error shown until I used the second '!'.
extension NSAlert {
func runModalSheetForWindow( aWindow: NSWindow ) -> Int {
self.beginSheetModalForWindow(aWindow) { returnCode in
NSApp.stopModalWithCode(returnCode)
}
let modalCode = NSApp.runModalForWindow(self.window as! NSWindow)
return modalCode
}
func runModalSheet() -> Int {
// Swift 1.2 gives the following error if only using one '!' below:
// Value of optional type 'NSWindow?' not unwrapped; did you mean to use '!' or '?'?
return runModalSheetForWindow(NSApp.mainWindow!!)
}
}
Unlike Windows I don't believe there's a way to block on modal dialogs. The input (e.g. the user clicking a button) will be processed on your main thread so there's no way of blocking.
For your task you will either have to pass the message up the stack and then continue where you left off.
When one object fails, stop processing the objects in the tree, make a note of which object failed (assuming that there is an order and you can pick up where you left off), and throw up the sheet. When the user dismisses the sheet, have the didEndSelector: method start processing again from the object that it left off with, or don't, depending on the returnCode.
- (bool) windowShouldClose: (id) sender
{// printf("windowShouldClose..........\n");
NSAlert *alert=[[NSAlert alloc ]init];
[alert setMessageText:#"save file before closing?"];
[alert setInformativeText:#"voorkom verlies van laatste wijzigingen"];
[alert addButtonWithTitle:#"save"];
[alert addButtonWithTitle:#"Quit"];
[alert addButtonWithTitle:#"cancel"];
[alert beginSheetModalForWindow: _window modalDelegate: self
didEndSelector: #selector(alertDidEnd: returnCode: contextInfo:)
contextInfo: nil];
return false;
}
You can use dispatch_group_wait(group, DISPATCH_TIME_FOREVER);:
dispatch_group_t group = dispatch_group_create();
dispatch_group_enter(group);
NSAlert *alert = [[NSAlert alloc] init];
[alert setMessageText:#"alertMessage"];
[alert addButtonWithTitle:#"Cancel"];
[alert addButtonWithTitle:#"Ok"];
dispatch_async(dispatch_get_main_queue(), ^{
[alert beginSheetModalForWindow:progressController.window completionHandler:^(NSModalResponse returnCode) {
if (returnCode == NSAlertSecondButtonReturn) {
// do something when the user clicks Ok
} else {
// do something when the user clicks Cancel
}
dispatch_group_leave(group);
}];
});
dispatch_group_wait(group, DISPATCH_TIME_FOREVER);
//you can continue your code here
Hope that helps.