Using NSSelector

To create a selector in Java, use NSSelector’s single constructor, which takes the method’s name and an array of the parameter types. Note that to obtain a Class object for a type, append .class to the type’s name. For example, the Class object for NSObject is NSObject.class and the Class object for boolean is boolean.class.

This code sample creates a selector for the doIt method:

void doIt(String str, int i) { . . . }

NSSelector sel =

    new NSSelector("doIt", new Class[] {String.class, int.class} );

To apply a selector on an object, use the overloaded instance method invoke. It performs the method that matches the selector and returns the result. If the target object does not have a method matching the selector, it throws NoSuchMethodException. The most basic form of invoke takes the target object and an Object array of the arguments. Other forms are convenience methods for selectors with no, one, or two arguments. Note that to pass an argument of a primitive type to invoke, use an object of the corresponding wrapper class. invoke converts the object back to the primitive type when it invokes the method. For example, to pass the float f, use new Float(f); and to pass the boolean value true, use new Boolean(true).

This code sample gives you two ways to apply the selector sel (defined above) to an object:

MyClass obj1 = new MyClass(), obj2 = new MyClass();

int i = 5;

sel.invoke(obj1, new Object[] { "hi", new Integer(i) });

sel.invoke(obj2, "bye", new Integer(10));

To create and apply a selector in one step, use the overloaded static method invoke. The basic form takes four arguments: the method name, an array of the parameter types, the target object, and an array of the arguments. Other forms are convenience methods for selectors with one or two arguments. This code sample shows two ways to create and apply a selector for the doIt method:

void doIt(String str, int i) { . . . }

MyClass obj1 = new MyClass(), obj2 = new MyClass();

int i = 5;

NSSelector.invoke("doIt", new Class[] {String.class, int.class},

    obj1, new Object[] {"hi", new Integer(i)});

NSSelector.invoke("doIt", String.class, int.class,

    obj1, "bye", new Integer(10));

Other methods return whether an object or class has a method that matches a selector (implementedByObject and implementedByClass) and returns the method name and parameter types for a selector (name and parameterTypes).