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15.3. Constructing, Setting, and Using Colors

Problem

You want to be able to obtain references to color objects in order to use them while you are drawing various forms on a view, such as text, rectangles, triangles and line segments.

Solution

Use the UIColor class.

Discussion

UIKit provides programmers with a high-level abstraction of colors, encapsulated in the UIColor object. This class has a few really handy class methods such as redColor, blueColor, brownColor, and yellowColor. However, if the color you are looking for isn’t one of the explicitly named UIColor methods, you can always use the colorWithRed:green:blue:alpha: class method of UIColor class to load the color that you are looking for. The return value of this class method is a value of type UIColor. The parameters of this method are:

red

The amount of red to use in the color. This value can be anything between 0.0f to 1.0f, where 0.0f omits all red and 1.0f makes the red component as dark as possible.

green

The amount of green to mix with the red in the color. This value also ranges from 0.0f to 1.0f.

blue

The amount of blue to mix with the red and green in the color. This value also ranges from 0.0f to 1.0f.

alpha

The opaqueness of the color. This value can range from 0.0f to 1.0f, with 1.0f making the color completely opaque and 0.0f making the color completely transparent (in other words, invisible).

After you have an object of type UIColor, you can use its set instance method to make the current graphics context use that color ...

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