CODEWITHSUNDEEP
cocoa
MikeMayer67
MikeMayer67

Reputation: 576

NSAlert beginSheetModalForWindow:completionHandler:

While setting up an NSAlert object to be displayed as a modal sheet in Xcode 5.0.2, I hit an interesting surprise.

I was planning on using beginSheetModalForWindow:modalDelegate:didEndSelector:contextInfo:

As I started to enter it, Xcode autofilled beginSheetModalForWindow:completionHandler: for me (even though I cannot find this in any NSAlert documentation).

I prefer to use completion handlers rather than delegate/selector as a callback mechanism, so I went ahead and tried it. I was pleasantly surprised to find that it worked perfectly.

Three quick questions before I commit to this.

  1. Am I missing something in the documentation?

  2. Is it "safe" to use this feature if it is undocumented? (i.e. will it magically disappear as mysteriously as it appeared?)

  3. I'd rather not hardcode the response values based on what I'm seeing via logging. Does anybody know the "proper" NS...Button constants?

Upvotes: 3

Views: 3128

Answers (1)

Wil Shipley
Wil Shipley

Reputation: 9553

This call is “safe” but it’s 10.9+ only. Here it is from the header file:

#if NS_BLOCKS_AVAILABLE
- (void)beginSheetModalForWindow:(NSWindow *)sheetWindow completionHandler:(void (^)(NSModalResponse returnCode))handler NS_AVAILABLE_MAC(10_9);
#endif

It appears they just accidentally left it out of the current docs. The headers are generally considered the “truth” in Cocoa, though—they authoritatively tell you what’s deprecated and what’s new. (Unlike in X11, for instance, where the documentation was declared to be correct over the actual implementations or the headers.)

These are the constants you want to use inside your completionHandler block:

/* These are additional NSModalResponse values used by NSAlert's -runModal and -beginSheetModalForWindow:completionHandler:.

   By default, NSAlert return values are position dependent, with this mapping:
       first (rightmost) button = NSAlertFirstButtonReturn
       second button = NSAlertSecondButtonReturn
       third button = NSAlertThirdButtonReturn
       buttonPosition 3+x = NSAlertThirdButtonReturn + x

   Note that these return values do not apply to an NSAlert created via +alertWithMessageText:defaultButton:alternateButton:otherButton:informativeTextWithFormat:, which instead uses the same return values as NSRunAlertPanel.  See NSAlertDefaultReturn, etc. in NSPanel.h
*/
enum {
    NSAlertFirstButtonReturn    = 1000,
    NSAlertSecondButtonReturn   = 1001,
    NSAlertThirdButtonReturn    = 1002
};

Upvotes: 8

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