Uiscrollview centre image weird code

First, CGRect is the typedef name for a struct type. CGRect is not a class, so the .frame member is not a property.

The { } notation is the initialized-struct notation for an unnamed struct. The unnamed struct is then assigned to the .frame member. Since the .frame member is a struct, the { } notation is permitted in struct assignments.

The {.origin=something, .size=otherthing} is a designated initializer. That is, within the { } initializer you designate the struct member names to be initialized. The classical struct initializer requires an in-order listing of just initializer values; you can't provide member names, so you have to know the exact order of members.

So the whole thing is roughly equivalent to:

Code:

CGRect r;  // struct definition (r is a CGRect struct)
r.origin = CGPointMake(0.0f, 0.0f);  // struct assignment of a CGPoint to r.origin
r.size = image.size;  // struct assignment of image.size to r.size
self.imageView.frame = r;  // struct assignment of r imageView.frame

In the last line, imageView is a property of self, but .frame is a struct member of that object.



Designated initializers were added in C99. See this wikipedia article:
http://en.wikipedia.org/wiki/Struct_(C_programming_language)#Struct_initialization

Also try some google searches for C designated initializer.

 

Not sure why you say that .frame is not a property of UIImageView and .frame is a struct member of UIImageView. frame is obviously a property of UIView and also is not a member struct of UIView.

But that isn't the interesting part of this code.

I would say it's more like this

Code:

whatever.frame = (CGRect){ 0, 0, image.size.width, image.size.height };

which is the C89 style of struct initialization
or

Code:

whatever.frame = CGRectMake(0, 0, image.size.width, image.size.height);

which requires no typecasts and is the usual way this is done.

I guess Wenderlich is using this notation to save a little space, or something.

 

You're right. That was a mistake. I became disoriented and wandered into a maze of dotty little passages all alike.