incompatible blocks type assigning

Question

I have used blocks a few times but never with declaring a typedef first.

I am trying to setup this definitions on a class (lets call it ClassA)

typedef void (^myBlock)();

@property (nonatomic, copy) myBlock onCompletion;

Then I create an instance of the object this class represents and do this:

ClassA *obj = [[ClassA alloc] init];
obj.onCompletion = ^(){
   // my code here
};

it is complaining "incompatible block pointer types assigning"...

can you guys explain?

Answer 1

尽管不必指定块的返回类型，但是如果块不带任何参数，则必须指定 void 。

Answer 2

Check out this link for block reference: block syntax

Just guessing it might be because you left the block parameter type blank.

typedef void (^myBlock)(void); //Untested

Answer 3

The only difference in the declared block type myBlock and the type of the block literal might be the return type.

If you leave the return type out in a block literal the compiler figures it out automatically:

myBlock block1 = ^() { // everything is fine
   return;
};

myBlock block2 = ^() { // does not work, types differ
   return 1;
};

Answer 4

At the request of the OP I am posting my original comment as an answer even though there are other answers stating the same thing:

You need to clearly specify that the block takes no parameters. Your typedef should be:

typedef void (^myBlock)(void);