PIMultiObserver

Combine multiple observations to trigger a single action

Overview

This Objective C frameworks allows combining multiple key-value observations, and calling a single notification callback with the result of the combined observations.

Usage

Example apps are included with this project. Here are the main use cases:

Creating A Multi Observer Controller

The controller is the object that manages multi-observations. To create:

#import <PIMultiObserver/PIMultiObserver.h>

...

PIMultiObserver *multiObserver = [[PIMultiObserver alloc] init];

Observing The AND Combination Of Properties

The method observeAnd takes a list of properties (objects and key paths) to observe, and a notification block. The block will be called whenever any of the properties change, with a Boolean parameter which is the AND combination of the current values of the observed properties:

- (void)observeAnd:(NSArray *)objectsAndKeyPaths block:(PIMONotificationBlock)block;

The example app Checklist is using this method to observe a set of rocket launch systems (think Apollo 13), in order to enable a "launch" button, when all subsystems are ready, but disable the button otherwise:

[multiObserver observeAnd:@[
    [PIObserver observerOf:self keyPath:@"booster"],
    [PIObserver observerOf:self keyPath:@"retro"],
    [PIObserver observerOf:self keyPath:@"fido"],
    [PIObserver observerOf:self keyPath:@"guidance"],
    [PIObserver observerOf:self keyPath:@"surgeon"]] 
    block:^(BOOL allSystemsGo) {
        self.launchButton.hidden = !allSystemsGo;
    }];

Observing All Properties To Become YES

The method observeAllYes takes a list of properties to observe and a notification block. The block is only called whenever all observed properties change to YES:

- (void)observerAllYes:(NSArray *)objectsAndKeyPaths block:(PIMONotificationBlock)block;

The example app Checklist is using this method to log an "All systems go!" message whenever all rocket launch systems become ready:

[multiObserver observeAllYes:@[
    [PIObserver observerOf:self keyPath:@"booster"],
    [PIObserver observerOf:self keyPath:@"retro"],
    [PIObserver observerOf:self keyPath:@"fido"],
    [PIObserver observerOf:self keyPath:@"guidance"],
    [PIObserver observerOf:self keyPath:@"surgeon"]]
    block:^(BOOL combinedValue) {
        NSLog(@"All systems go!");
    }];

Mapping Properties To Booleans

Individual observations (created with PIObserver) can map their property values to Booleans using an optional mapper block.

The example app Checklist is mapping its temperature property to YES/NO depending if the temperature is within an allowed range:

[multiObserver observeAnd:@[
    // ...
    [PIObserver observerOf:self keyPath:@"temp" mapper:^BOOL(NSNumber *t) {
        return t.floatValue >= MinLaunchTemp && t.floatValue <= MaxLaunchTemp;
    }]]
    block:^(BOOL combinedValue) {
        self.launchButton.hidden = !combinedValue;
    }];

Implementation Details

• Multi-observations are implemented using Cocoa key-value observations

• After setting up a multi-observation, the notification block is called immediately, if the evaluation criteria is met

• Upon dealloc the controller removes all observations

• Notification blocks are always called on the main thread

• Mapper blocks are called on the same thread as the Cocoa KVO

Installation

Manual installation: Add the source files from PIMultiObserver to your project.

CocaPods: Coming soon.

License

PIMultiObserver is released under the MIT License. See LICENSE for more details.