How do i implement a message box in a Cocoa application? - cocoa

Question

I have implemented delete functionality in cocoa application now i want to show one message box when user click on delete button.

Answer 1

Take a look at NSAlert, which has a synchronous -runModal method:
NSAlert *alert = [[[NSAlert alloc] init] autorelease];
[alert setMessageText:#"Hi there."];
[alert runModal];
As Peter mentions, a better alternative is to use the alert as a modal sheet on the window, e.g.:
[alert beginSheetModalForWindow:window
modalDelegate:self
didEndSelector:#selector(alertDidEnd:returnCode:contextInfo:)
contextInfo:nil];
Buttons can be added via -addButtonWithTitle::
[a addButtonWithTitle:#"First"];
[a addButtonWithTitle:#"Second"];
The return code tells you which button was pressed:
- (void) alertDidEnd:(NSAlert *)a returnCode:(NSInteger)rc contextInfo:(void *)ci {
switch(rc) {
case NSAlertFirstButtonReturn:
// "First" pressed
break;
case NSAlertSecondButtonReturn:
// "Second" pressed
break;
// ...
}
}

Answer 2

Long time has passed since the accepted answer and things have changed:
Swift is becoming more and more popular.
beginSheetModalForWindow(_:modalDelegate:didEndSelector:contextInfo:) is deprecated, we should use beginSheetModalForWindow:completionHandler: instead.
Latest code sample in Swift:
func messageBox() {
let alert = NSAlert()
alert.messageText = "Do you want to save the changes you made in the document?"
alert.informativeText = "Your changes will be lost if you don't save them."
alert.addButtonWithTitle("Save")
alert.addButtonWithTitle("Cancel")
alert.addButtonWithTitle("Don't Save")
alert.beginSheetModalForWindow(window, completionHandler: savingHandler)
}
func savingHandler(response: NSModalResponse) {
switch(response) {
case NSAlertFirstButtonReturn:
println("Save")
case NSAlertSecondButtonReturn:
println("Cancel")
case NSAlertThirdButtonReturn:
println("Don't Save")
default:
break
}
}
In case you want a synchronous version:
func messageBox() {
let alert = NSAlert()
alert.messageText = "Do you want to save the changes you made in the document?"
alert.informativeText = "Your changes will be lost if you don't save them."
alert.addButtonWithTitle("Save")
alert.addButtonWithTitle("Cancel")
alert.addButtonWithTitle("Don't Save")
let result = alert.runModal()
switch(result) {
case NSAlertFirstButtonReturn:
println("Save")
case NSAlertSecondButtonReturn:
println("Cancel")
case NSAlertThirdButtonReturn:
println("Don't Save")
default:
break
}
}