Getting gst-objc

(If you have a better name idea feel free to give me suggestions.)

You can fetch the source from github:

$ git clone git://github.com/mathk/gst-objc.git

Then you have to build it.

$ autoreconf -vi
$ ./configure
$ make
$ [sudo] make install

Depending on you platform you may need gnustep. You can find all the instruction to build gnustep here

Here you should be able to load Objc package:

GNU Smalltalk ready

st> PackageLoader fileInPackage: 'Objc'
Loading package Objc
2011-05-01 22:17:52.971 gst[91826:903] Load complete
PackageLoader
st> 

First window

Now that you can load Objc, I will show you how to create an NSWindow. For convenience I will drop every thing in a file myFirstWindow.st.

"First load the package"
Eval [
  PackageLoader fileInPackage: 'Objc'.
]

After that we need to create an NSApplication that will handle the main event loop.

nsApplication := Objc.NSApplication.
nsApp := nsApplication sharedApplication.

As you can see, when sending #sharedApplication to the object, you are in fact forwarding the message to Objective-C.

We can then create our first NSWindows:

nsRect := Objc.NSRect gcOriginX: 0.0
                              y: 0.0
                          width: 100.0
                         height: 100.0.

nsWindow := Objc.NSWindow alloc.
nsWindow initWithContentRect: nsRect 
	               styleMask: 15 
                     backing: Objc.ObjcAppKit nsBackingStoreBuffered 
                       defer: (Character value:1).
nsWindow setTitle: 'Test windows'.

nsRect is just a CStruct that tell which size the window is going to have. #initWithContentRect:styleMask:backing:defer: and #setTitle: are again forwarded to Objective-C. You have to be careful to chose the right type when passing argument to Ojective-C. For instance the last parameter is of type 'c' in Objective-C which is a Character.

Notice that Smalltalk's String is convert to Objective-C's NSString automatically.

After that we have to create a NSView. The way NSWindow handles the drawing is by calling #drawRect: on a view. So we have to subclass NSView and implement the #drawRect: method.

The way to do this is by using class and method pragma.

Objc.ObjcObject subclass: MyNSView [
  <objcSubclass: 'NSView'>

  drawRect: rect [
    <objc>
    Objc.NSColor redColor set.
    Objc.ObjcAppKit nsRectFill: self bounds
  ]
]

The pragma objcSubclass: tells what is the super class. In other words MyNSView is a subclass of NSView.

The pragma objc tells Objective-C to add a method to the class newly created thus letting Objective-C to call into Smalltalk. Because #drawRect: is define somewhere in the NSView's hierarchy you don't need to specify the type of the method.

For arbitrary method you need to specify the type expected for parameters and return value using the objcReturnning:args: pragma.

The #drawRect: method is pretty simple. It just fills the window in red.

Now we can use this newly created class:

"Create a new view but don't retain it. Instead autorelease it."
view := MyNSView alloc init.
view autorelease.

nsWindow setContentView: view.
nsWindow center.
nsWindow orderFrontRegardless.
nsWindow contentView.
nsApp run

At this point you should see a small window fill of red.

Last I would like to thanks Paolo Bonzini and David Chisnall for theirs help and advice and also thanks the kind review of this document by Jonathan Sterling

Complete code:

Eval [
  PackageLoader fileInPackage: 'Objc'.
]

Objc.ObjcObject subclass: MyNSView [
  <objcSubclass: 'NSView'>

  drawRect: rect [
    <objc>
    Objc.NSColor redColor set.
    Objc.ObjcAppKit nsRectFill: self bounds
  ]
]

Eval [
  | view nsApp nsRect nsWindow |

  nsApp := Objc.NSApplication sharedApplication.
  nsRect :=  Objc.NSRect gcOriginX: 0.0
                                 y: 0.0
                             width: 100.0
                            height: 100.0.

  nsWindow :=  Objc.NSWindow alloc.
  	       initWithContentRect: nsRect 
                     styleMask: 15
                       backing: Objc.ObjcAppKit nsBackingStoreBuffered 
                         defer: (Character value:1).

  nsWindow setTitle: 'Test windows'.

  view := MyNSView alloc init.
  view autorelease.

  nsWindow setContentView: view.
  nsWindow center.
  nsWindow orderFrontRegardless.
  nsWindow contentView.
  nsApp run
]