how do i know when to use a datasource or delegate protocol when using a UI object in my project?

for example the UIPickerView, in the tutorial that i am learning i had to include the datasource and delegate protocols in my project for the pickerview to work开发者_开发知识库. how would i know on other objects?

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In general that is explained in the documentation of the individual object. For example http://developer.apple.com/iphone/library/documentation/UIKit/Reference/UIPickerView_Class/Reference/UIPickerView.html

In the Overview section it explains that, "the delegate must adopt the UIPickerViewDelegate protocol" and that, "the data source must adopt the UIPickerViewDataSource protocol"

From http://developer.apple.com/iphone/index.action just type the name of the object you are interested in into the search box and the documentation should explain everything needed to make it go.

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To note, the UIPickerViewDelegate/Datasource are representative of the Delegate design pattern (see Cocoa Design Patterns) and are repeated throughout the Cocoa UI hierarchy as a method of modifying behavior of an object without having to subclass. It's quite graceful, less entropic, fosters the single responsibility principle, and reduces coupling. The delegation pattern is seen throughout all of Cocoa, not just the UI classes, so you can expect to see it often.

To know about other objects, you pretty much have to visit the Framework Library Reference for the specific class at the Apple Developer Center or from within the help system of Xcode. You can almost presume that all data backed UI objects will have datasource (delegate) methods, and most UI objects will have delegate methods.