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Objective-c Tricks2014 – Jan

By: Hossam Ghareeb

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Use Literals

The following is the old way of writing code:

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The same code can be written as follows:

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Subscripting

You can use subscripting to access the values inside dictionaries and arrays. This is how the syntax looks:

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Classes And Selectors From Strings

We can dynamically generate classes and selectors from strings,  We do this by using the NSClassFromString and NSSelectorFromString functions:

NSClassFromString will return nil if there isn't a class in the runtime that matches the string

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We can also decide in run time which selector to be called based on input:

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Method Swizzling Methods are made up of two components. The selector, which is an identifier

for a method, and the IMP, which is the actual implementation that is run. One of the key things about this separation is that a selector and IMP link can be changed. One IMP can have multiple selectors pointing to it.

Subclassing -> This allows you to override a method and call the original implementation, but it means that you have to use instances of this subclass.

Category -> you cannot call the original implementation if you override a method.

Swizzling -> You can override a method without subclassing AND call the original implementation

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Example make a UINavigationBar green

T this will change all navigation bars in the

app to green, but if I used UIImagePickerController it will be changed too!!!. We have to find new way for that >>>>> Method Swizzling

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Method Swizzling Cont. Method swizzling, in short, is switching methods at runtime. So

you can say for UINavigationBar don’t use the standard drawRect:, but instead swap it with a different one

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Here is the swizzling:

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Another problem solved by Swizzling

 measure how long the synchronize takes in NSUserDefaults

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Cont.

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Example 2

Borders around all UIViews initWithFrame: get a red border,

views that were unarchived (for example as part of XIBs) get a blue border.

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Surprise  the status bar at the top ofan iOS app is drawn by the app itself

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How to do that?

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Cont.

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Other tricks objc_msgSend()

This function takes a target, a selector and a list of arguments

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CGRect Tricks Shrink CGRect:

Different insets for each edge:using UIEdgeInsets(top, left, bottom, right)

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Cont.

CGRectUnion is UIScrollView’s best friend:if you want use UIScrollView with bunch of subviews, so you have to know only the top-left and bottom-right views:

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Cont.

Dictionary Representation (to store in in plist on disk):

Print CGRect values :

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Cont. Storing it in Obj-C Storage Classes

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Thank you

Any Questions?