Apple WebObjects 3.5 Instrukcja Użytkownika Pobierz pdf (Strona 132)

Chapter 7 Managing State

132

• During unarchiving, an EOEditingContext can recreate individual objects

in the graph only as they are needed by the application. This approach can

signiﬁcantly improve an application’s perceived performance.

An enterprise object (like any other object that uses the OpenStep archiving

scheme) makes itself available for archiving by declaring that it conforms to the

NSCoding protocol and by implementing the protocol’s two methods,

encodeWithCoder: and initWithCoder:. It implements these methods like this:

// WebScript example

- encodeWithCoder:(NSCoder *)aCoder {

[EOEditingContext encodeObject:self withCoder:aCoder];

}

- initWithCoder:(NSCoder *)aDecoder {

[EOEditingContext initObject:self withCoder:aDecoder];

return self;

}

Even though the Java packages provide a different archiving mechanism, your

Java classes should use the Foundation archiving mechanism. In Java, the

NSCoding protocol is called the Coding interface, and it declares only one

method,

encodeWithCoder. If your class conforms to the Coding interface, it should

also implement a constructor that takes a Coder object as an argument. (This is

the equivalent of the

initWithCoder: method.)

// Java example

public void encodeWithCoder(Coder aCoder) {

EditingContext.encodeObjectWithCoder(this, aCoder);

}

public MyClass(Coder aDecoder) {

EditingContext.initObjectWithCoder(this, aDecoder);

}

The enterprise object simply passes on responsibility for archiving and

unarchiving itself to the EOEditingContext class, by invoking the

encodeObject:withCoder: and initObject:withCoder: class methods and passing a reference to

itself (

self) as one of the arguments. The editing context takes care of the rest.

(See the EOEditingContext class speciﬁcation in the Enterprise Objects Class

Reference for more information.)

Archiving Custom Objects in Other Applications

Custom classes that can’t take advantage of an EOEditingContext for archiving

must take a different approach. These classes still must conform to the

NSCoding protocol and implement its

encodeWithCoder: and initWithCoder: methods;

however, you must implement them differently. In

encodeWithCoder:, you use the

coder argument provided to encode the object’s instance variables. In

initWithCoder:, the object uses the decoder provided to initialize itself.

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