What We’ve Learned

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<span xmlns="http://www.w3.org/1999/xhtml" xmlns:epub="http://www.idpf.org/2007/ops" class="toc-secnum">14. </span>Viewing and Editing PhotosViewing and Editing Photos

What We’ve Learned

images/gestures/user-image-scene-clipped.png

In this chapter, we took hold—literally—of the touch gestures that are the hallmark of iOS user interfaces. By giving the user the ability to manipulate an image by dragging it around with one finger and pinch-zooming it with two, we immediately create a sense of close contact with the image. Gesture recognizers make it easy to pick up the most common touch gestures and have them call back to our code when gestures are detected. And because both the recognizers and the onscreen views are concerned with how much movement or scaling is indicated by a gesture, it works well to connect the two by means of affine transforms, which cleanly represent translation, rotation, scaling, and combinations thereof.

Armed with this knowledge, we can bring new touch handling features to scenes throughout our app. It will also be useful if we ever need to create our own custom views, since a view is basically a combination of appearance and interactivity, meaning that a custom view just needs to handle custom drawing and custom event-handling. And we just saw how to do the second of those things.

The new iPhone 6s and 6s Plus introduce a new kind of gesture, 3D Touch, which is a touch that is sensitive to how much force the user is applying. In other words, it can tell the difference between “soft” and “hard” presses.

Apple suggests developers use 3D Touch for “peek” and ”pop” gestures, which preview an item’s contents without fully opening it. For example, we could add a hard-press gesture to user icons on the table of tweets, so we could pop up a little preview of a user’s info without having to drill through two scenes to the user’s detail scene.

We’ve chosen not to create an example for 3D Touch, because the support in iOS 9 is pretty limited so far. In particular, it is not supported in the iOS Simulator, so the only way to try it out is to actually get one of the new iPhone models. Still, it’s worth looking at how it works.

None of the gesture recognizers know anything about 3D Touch. Instead, the only access we have is through the UITouch objects delivered to touchesBegan, touchesMoved, and touchesEnded, the low-level methods we dismissed at the beginning of the chapter as “a pain in the butt.”

To detect these touches, we would need to subclass UIView, and check its traitCollection for a trait called forceTouchCapabililty (notice that the APIs use the term “force touch” rather than the marketing name “3D Touch”). If force touch is available, an override of touchesBegan could go over the Set of UITouches it receives and measure their force property. This value indicates how hard the touch was, from 1.0 for a “normal” touch up to a predefined maximumPossibleForce.

If the code determines the force is strong enough, it should then take some appropriate action, like showing a menu. However, good MVC says that kind of application logic doesn’t go in the view, but rather in a controller. So we’d need a way to have a view controller handle the force touch event, like by having the view call back to the controller (the familiar delegate pattern), or having the controller give the view a closure to run whenever it gets a force touch.

Maybe iOS 10 will have gesture recognizers that provide the force of their touches. For now, handling 3D Touch is possible but kind of a hassle.

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What We’ve Learned

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What We’ve Learned