iPad Application Development For Dummies, 3rd Edition

Rotating the Object

In this section, I show you how to rotate a view (in this case, turn the car around). To do so, you update the rotate code stub we started out with back in Listing 10-2 with the bolded code in Listing 10-4.

Listing 10-4: Updating rotate

- (void)rotate {

CGAffineTransform transform = CGAffineTransformMakeRotation(M_PI);

void (^animation)() = ^() {

car.transform = transform;

};

void (^completion)(BOOL) = ^(BOOL finished){

[self returnCar];

};

[UIView animateWithDuration:3 animations:animation completion:completion];

}

This method uses the block declarations I explain in the previous section.

The CGAffineTransform data structure represents a matrix used for affine transformations — a blueprint for how points in one coordinate system map to points in another coordinate system. Although CGAffineTransform has a number of uses (such as scaling and translating a coordinate system), the only one covered here is the rotation method you use in Listing 10-4:

CGAffineTransformMakeRotation(M_PI)

To rotate a view, you specify the angle (in radians) to rotate the coordinate system axes. Whereas degrees are numbers between 0 and 360, radians, though similar, range from 0 to 2*pi. So when you create a rotation that turns an object around one half-circle, that rotation in radians is pi. (M_PI is a system constant that represents pi.)

Just to make your life ...