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Implementing the Model

Now it’s time to define the behavior of the functions you declared in Converter.h.

1. In the Classes group of the Groups & Files menu, double-click Converter.m to open the file for editing.

2. Create the getters and setters for the two member variables—sourceCurrencyAmount and rate.

   Remember you used @property to create the prototypes for the getter and setter methods in Converter.h. If you provide a getter and setter (or just a getter in the case of a read-only property) method implementation for a property, you don’t need to do anything more. Commonly, however, you use the @synthesize directive in @implementation blocks to trigger the compiler to generate accessor methods for you.

   Add the following line into Converter.m after the @implementation Converter line:

   @synthesize sourceCurrencyAmount, rate;

   This line defines the body of the getter and setter methods for the variables sourceCurrencyAmount and rate based on the properties you set in the Converter.h file.

   Note: For more information on properties and the various options available, read “Properties” in The Objective-C 2.0 Programming Language.

Define the convertCurrency Method

Insert the highlighted lines in Listing 3-2 into Converter.m.

Listing 3-2  Definition of the convertCurrency method in Converter.m

#import "Converter.h"

@implementation Converter

@synthesize sourceCurrencyAmount, rate;

- (float)convertCurrency {

    return self.sourceCurrencyAmount * self.rate;

}

@end

The convertCurrency method multiplies the values of the converter class’s two member variables and returns the result.

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