Once we have a window on the screen, we might like to put + something in it. Let's start by adding a button.
+ +Creating a button object is as simple as creating a window + object; we simply allocate one:
+ ++(setf my-button (#/alloc ns:ns-button)) +#<NS-BUTTON <NSButton: 0x13b7bec0> (#x13B7BEC0)> ++ +
As with the window, most of the interesting work is in + configuring the allocated button after it's allocated.
+ +Instances of NSButton include pushbuttons with either text or
+ image labels (or both), checkboxes, and radio buttons. In order to
+ make a text pushbutton, we need to tell our button to use a
+ button-type of NSMomentaryPushInButton, an image
+ position of NSNoImage, and a border style
+ of NSRoundedBezelStyle. These style options are
+ represented by Cocoa constants.
We also need to give the button a frame rectangle that defines
+ its size and position. We can once again
+ use ns:with-ns-rect to specify a temporary rectangle
+ for the purpose of initializing our button:
+(ns:with-ns-rect (frame 10 10 72 32) + (#/initWithFrame: my-button frame) + (#/setButtonType: my-button #$NSMomentaryPushInButton) + (#/setImagePosition: my-button #$NSNoImage) + (#/setBezelStyle: my-button #$NSRoundedBezelStyle)) +;Compiler warnings : +; Undeclared free variable MY-BUTTON (4 references), in an anonymous lambda form +NIL ++ +
Now we just need to add the button to the window:
+ ++(#/addSubview: (#/contentView my-window) my-button) ++ +
The button appears in the window with the rather uninspired + label "Button". Clicking it highlights the button but, since we + didn't give it any action to perform, does nothing else.
+ +We can give the button a more interesting label and, perhaps + more importantly, an action to perform, by passing a string and an + action to it. First, let's set the button title:
+ ++(let ((label (%make-nsstring "Hello!"))) + (#/setTitle: my-button label) + (#/release label)) +;Compiler warnings : +; Undeclared free variable MY-BUTTON, in an anonymous lambda form +NIL ++ +
The button changes to display the text "Hello!". Notice that we + are careful to save a reference to the label text and release it + after changing the button title. The normal memory-management + policy in Cocoa is that if we allocate an object (like the + NSString "Hello!") we are responsible for releasing it. Unlike + Lisp, Cocoa does not automatically garbage-collect all allocated + objects by default.
+ +Giving the button an action is slightly more + complicated. Clicking a button causes the button object to send a + message to a target object. We haven't given our button a message + to send, nor a target object to send it to, so it doesn't do + anything. In order to get it do perform some kind of action, we + need to give it a target object and a message to send. Then, when + we click the button, it will send the message we specify to the + target we provide. Naturally, the target object had better be able + to respond to the message, or else we'll just see a runtime + error.
+ +Let's define a class that knows how to respond to a greeting + message, and then make an object of that class to serve as our + button's target.
+ +We can define a subclass of NSObject to handle
+ our button's message:
+(defclass greeter (ns:ns-object) + () + (:metaclass ns:+ns-object)) +#<OBJC:OBJC-CLASS GREETER (#x13BAF810)> ++ +
We'll need to define a method to execute in response to the + button's message. Action methods accept one argument (inaddition + to the receiver): a sender. Normally Cocoa passes the button + object itself as the sender argument; the method can do anything + it likes (oor nothing at all) with the sender.
+ +Here's a method that displays an alert dialog:
+ ++(objc:defmethod #/greet: ((self greeter) (sender :id)) + (declare (ignore sender)) + (let ((title (%make-nsstring "Hello!")) + (msg (%make-nsstring "Hello, World!")) + (default-button (%make-nsstring "Hi!")) + (alt-button (%make-nsstring "Hello!")) + (other-button (%make-nsstring "Go Away"))) + (#_NSRunAlertPanel title msg default-button alt-button other-button) + (#/release title) + (#/release msg) + (#/release default-button))) ++ +
Now we can create an instance of the Greeter class and use it + as the button's target:
+ ++(setf my-greeter (#/init (#/alloc greeter))) +#<GREETER <Greeter: 0x136c58e0> (#x136C58E0)> + +(#/setTarget: my-button my-greeter) +NIL + +(#/setAction: my-button (@SELECTOR "greet:")) +NIL ++ +
Now, if you click the button, an Alert panel appears.
+ +