nsobject

问题 I've seen code like: if (delegate != nil && [delegate respondsToSelector:@selector(doSomething)]) ... But, sending a message to nil just returns nil (which evaluates to NO ), so why not just do: if ([delegate respondsToSelector:@selector(doSomething)]) ... Is the former faster if delegate == nil ? Either way, I prefer the latter cause it's less code. And, less is better than more . Every Unix pro knows that. 回答1: objc_msgSend, the function used to send dynamic messages in Objective-C

问题 This code is legal in Swift: class Snapper : NSObject { var anim : UIDynamicAnimator init(referenceView:UIView) { self.anim = UIDynamicAnimator(referenceView:referenceView) // super.init() } } Observe that in my initializer I didn't call super.init() ; I commented out that line. But the Swift compiler doesn't complain. Why? I thought there was a rule that your designated initializer must call a designated initializer of its superclass. And I have a superclass, namely NSObject. Is this a bug?

问题 I would like to take the GCD approach of using shared instances to the next step so I created the following code: @implementation MyClass static id sharedInstance; #pragma mark Initialization + (instancetype)sharedInstance { static dispatch_once_t once; dispatch_once(&once, ^{ sharedInstance = [[self alloc] init]; }); return sharedInstance; } - (instancetype)init { if (sharedInstance) { return sharedInstance; } @synchronized(self) { self = [super init]; if (self) { sharedInstance = self; }

问题 I'm working in Objective-C on the iPhone and need to know whether a 'Class' inherits from 'NSObject'. I tried checking if it responds to an NSObject selector: bool success = [myClass respondsToSelector:@selector(class)]; but you can guess what happened... it didn't even respond to "respondsToSelector:" so it throws a "does not implement doesNotRecognizeSelector:" exception. I tried to catch that exception, but it looks like it can't be caught with a @try-@catch. Any ideas? 回答1: Go direct to

问题 How is it possible to convert an Object instance to NSObject one? I've created a NSDictionary from NSDictionary.FromObjectAndKey(); This method wants an NSObject but I have custom object to pass in: int key = 2341; var val = new MyClass(); NSDictionary.FromObjectAndKey(val, key); // obviously it does not work!! How to fix this? Thank you in advance. 回答1: You can not convert an arbitrary object into an NSObject. The NSObject.FromObject will try to wrap common data types like numbers, strings,

问题 How is it possible to convert an Object instance to NSObject one? I've created a NSDictionary from NSDictionary.FromObjectAndKey(); This method wants an NSObject but I have custom object to pass in: int key = 2341; var val = new MyClass(); NSDictionary.FromObjectAndKey(val, key); // obviously it does not work!! How to fix this? Thank you in advance. 回答1: You can not convert an arbitrary object into an NSObject. The NSObject.FromObject will try to wrap common data types like numbers, strings,

问题 Basically, I have the following code (explained here: Objective-C Constants in Protocol) // MyProtocol.m const NSString *MYPROTOCOL_SIZE; const NSString *MYPROTOCOL_BOUNDS; @implementation NSObject(initializeConstantVariables) +(void) initialize { if (self == [NSObject class]) { NSString **str = (NSString **)&MYPROTOCOL_SIZE; *str = [[MyClass someStringLoadedFromAFile] stringByAppendingString:@"size"]; str = (NSString **)&MYPROTOCOL_BOUNDS; *str = [[MyClass someStringLoadedFromAFile]

问题 Here's a very simple class (subclass of NSObject ) that keeps a list of CGPath objects and appends one CGPath to the array on init : import Foundation class MyClass: NSObject { var list = [CGPath](); init() { list.append(CGPathCreateMutable()); } } When trying to use this class: var instance = MyClass(); println(instance.list.count); // runtime error after adding this line Yields an ugly crash: Playground execution failed: error: Execution was interrupted, reason: EXC_BAD_INSTRUCTION (code

问题 What is the purpose/use of NSObject in Objective-C? I see classes that extend NSObject like this: @interface Fraction : NSObject In C++ or Java, we don't use any variables like NSObject even though we have preprocessor directives and import statements in both Objective-C and Java. Why do classes explicitly inherit from NSObject in Objective-C? What are the consequences of not declaring inheritance from NSObject? 回答1: We use NSObject to explicitly state what a given class inherits from. I'm

问题 Greetings, I have a view based application project where I have created an NSObject class called "SquareClass". Now, from the Xcode's interface builder, I want to be able to instantiate that "SquareClass" into a square object with global scope, in such a way that, when I create actions from any UI controls(i.e textboxes, buttons etc...), I want to be able to call methods of that object within those actions. example: (void)MyAction1:(id)color { [square setColor:color]; } (void)MyAction2:(id