Rework multi-transition support using a recursive composition API #43

jverkoey · 2017-09-13T18:08:13Z

This largely reworks the changes made in #40.

This new API supports a recursive model for building modular transitions. Every view controller transition is now governed by a single root transition. This root transition can then compose out to child transitions if it so chooses. A view controller transition is complete once every transition in the tree is complete.

This pattern provides clear solutions for how to handle data passing and sharing between modular transitions, as seen most clearly in the PhotoAlbumTransition example which makes heavy use of transition composition and view duplication.

There are four major parts to this change:

Updated the README documentation.
Updated the examples.
Added the functionality.
Added more tests.

README

The readme's intro tutorial on how to build a transition has been updated.

Updated examples

The photo album transition example has been updated to make use of compositional transitions. Its transition hierarchy looks like so:

Added functionality

The new compositional functionality is made visible to clients through TransitionContext's new API compose(with:). For example:

context.compose(with: FadeTransition(target: .foreView, style: .fadeIn))
context.compose(with: SpringFrameTransition(target: .target(snapshotContextView),
                                            size: fitSize))

The implementation of the tree-based compositional structure is found in MDMViewControllerTransitionCoordinator.m.

Added tests

There are new tests for validating certain features of the transitioning stack, including the new compositional APIs.

Future plans

With this architecture in place, we'll be able to start deploying a library of pre-made transitions that clients can piece together to build complex transitions. These transitions will go in a separate MaterialMotion Objective-C library, making use of both MotionTransitioning and MotionAnimator.

This reverts the `transitions` API changes introduced in 8653958 and replaces it with a recursive model for transition composition.

jverkoey · 2017-09-25T16:23:39Z

src/MDMTransitionContext.h

+ eventually invoke transitionDidEnd. Only once both the parent transition and all of its children
+ (and their children) have completed will the overall view controller transition be completed.
+ */
+- (void)composeWithTransition:(nonnull id<MDMTransition>)transition;


Feedback requested on this API name.

jverkoey · 2017-09-25T16:24:13Z

src/MDMTransitionController.h


 This may be non-nil while a transition is active.
 */
-@property(nonatomic, strong, nullable, readonly) NSArray<id<MDMTransition>> *activeTransitions;
+@property(nonatomic, strong, nullable, readonly) id<MDMTransition> activeTransition;


The changes here are mostly reverting the changes introduced in 8653958.

jverkoey · 2017-09-25T16:24:41Z

src/MDMTransitionPresentationController.m

@@ -113,6 +113,8 @@ - (void)startWithContext:(NSObject<MDMTransitionContext> *)context {

    [UIView animateWithDuration:context.duration animations:^{
      self.scrimView.alpha = context.direction == MDMTransitionDirectionForward ? 1 : 0;
+    } completion:^(BOOL finished) {
+      [context transitionDidEnd];


Presentation controllers also need to inform the context of completion.

jverkoey · 2017-09-25T16:26:26Z

src/private/MDMViewControllerTransitionCoordinator.m

 @end

-@protocol MDMViewControllerTransitionContextDelegate <NSObject>
- (void)transitionContextDidEnd:(MDMViewControllerTransitionContext *)context;
+@interface MDMViewControllerTransitionContextNode : NSObject <MDMTransitionContext, MDMViewControllerTransitionContextNodeParent>


Typical parent/node design pattern here. The parent protocol only exposes APIs needed by the child to communicate upwards.

jverkoey · 2017-09-25T16:28:07Z

src/private/MDMViewControllerTransitionCoordinator.m

 @end

-@implementation MDMViewControllerTransitionContext {
+@implementation MDMViewControllerTransitionContextNode {
+  // Every node points to the same array in memory.


This is a minor simplification: by sharing the same mutable array, every node can add to a single shared pool of completion blocks. The alternative would be to route messages up the parent hierarchy, but given that this is a private implementation detail I wasn't particularly concerned with such an approach.

jverkoey · 2017-09-25T16:29:13Z

src/private/MDMViewControllerTransitionCoordinator.m

+  }
+
+  if (!anyChildActive && _didEnd) { // Inform our parent of completion.
+    [_parent childNodeTransitionDidEnd:self];


Bubbles completion up the tree.

jverkoey · 2017-09-25T16:47:36Z

Hi reviewers, I've left some comments to help guide review of the source.

jverkoey · 2017-09-26T22:03:10Z

Gentle ping.

ajsecord

And Lo! In the days of [REDACTED], there was a strange silence upon the land, wherein the voices of many were missing or muted. Houses went unbuilt, promises were not kept, and there was a general uneasiness about all.

jverkoey force-pushed the composition branch from d136a15 to dd3f093 Compare September 13, 2017 20:20

jverkoey force-pushed the composition branch 4 times, most recently from a5c06fe to adf9694 Compare September 21, 2017 16:55

jverkoey changed the title ~~WIP of composition API.~~ Rework multi-transition support using a recursive composition API Sep 21, 2017

jverkoey force-pushed the composition branch from adf9694 to 82df7ea Compare September 21, 2017 18:15

jverkoey requested review from ianegordon and ajsecord September 21, 2017 18:34

jverkoey force-pushed the composition branch 7 times, most recently from 58fd3bc to c11ac32 Compare September 22, 2017 22:18

Rework multi-transition support using composition.

d8a081f

This reverts the `transitions` API changes introduced in 8653958 and replaces it with a recursive model for transition composition.

jverkoey commented Sep 25, 2017

View reviewed changes

jverkoey force-pushed the composition branch from c11ac32 to d8a081f Compare September 25, 2017 16:46

ajsecord approved these changes Sep 26, 2017

View reviewed changes

jverkoey merged commit 0b57361 into develop Sep 27, 2017

jverkoey deleted the composition branch September 27, 2017 19:03

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Rework multi-transition support using a recursive composition API #43

Rework multi-transition support using a recursive composition API #43

jverkoey commented Sep 13, 2017 •

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Rework multi-transition support using a recursive composition API #43

Rework multi-transition support using a recursive composition API #43

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jverkoey commented Sep 13, 2017 • edited Loading

README

Updated examples

Added functionality

Added tests

Future plans

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jverkoey commented Sep 13, 2017 •

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