Error on init of custom class in objective c-CodePudding

I use the following code to alloc and init a class in objective c. The class is a cocoa touch class. I try to initialize the class with the code below.

   MyClass *myClass;
   myClass=[MyClass alloc];
   myClass=[MyClass init];

It crashes at

myClass=[MyClass init];

saying

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '***  [MyClass<0x100b075d0> init]: cannot init a class object.'

If i use

myClass=[[MyClass alloc] init];

It works. Any idea why this happens?

CodePudding user response：

[MyClass alloc] calls the alloc method on the class MyClass. It returns an instance of MyClass, ready to be initialised, which you do by calling init on the returned instance.

Classically you write [[MyClass alloc] init] in Objective-C because there's nothing you can or should be doing between allocating and initialising.

In your code, [MyClass init] is treating init like a class method, which it is not.

MyClass *myClass;
myClass = [MyClass alloc];
myClass = [myClass init];

Would probably work (note I'm calling init on myClass, not MyClass, but it would upset any future readers and make them wonder why you're not just doing it the normal way.