Apple WebObjects 3.5 Bedienungsanleitung PDF herunterladen (Seite 107)

Designing for Reusability

107

• Provide attributes for all signiﬁcant features.

The more customizable a component is, the more likely it is that

people will be able to reuse it. For example, if the AlertPanel

component discussed in “Intercomponent Communication” (page 98)

let you set the titles of the hyperlinks (say, to OK and Cancel, or Send

Now and Send Later), the panel could be adapted for use in many

more applications.

• Provide default values for attributes wherever possible.

Don’t require people to set more attributes than are strictly required

by the design of your reusable component. In your component’s

initialization method, you can provide default values for optional

attributes. When the component is created, the attribute values

speciﬁed in the initialization method are used unless others are

speciﬁed in the parent’s declarations ﬁle.

For example, the AlertPanel component’s

init method could set these

default values:

- init {

[super init];

alertString = @"Alert!";

alertFontColor = @"#ff0000";

alertFontSize = 6;

infoString = @"User should provide an infoString";

infoFontColor = @"#ff0000";

infoFontSize = 4;

borderSize = 2;

tableWidth = @"50%";

return self;

}

Then, in a declarations ﬁle, you are free to specify all or just a few

attributes. This declaration speciﬁes values for all attributes:

Complete Declaration

ALERT: AlertPanel {

infoString = message;

infoFontSize = 4;

infoFontColor = "#500000";

alertString = "New Release";

alertFontColor = "#A00000";

alertFontSize = 6;

tableWidth = "50%";

};

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