updated README with initStepCountObserver docs

README.md

@@ -20,10 +20,8 @@ A React Native bridge module for interacting with [Apple HealthKit] data.
       * [getBiologicalSex](#getbiologicalsex)
       * [getDateOfBirth](#getdateofbirth)
       * [getStepCount](#getstepcount)
-      * ~~[getStepCountForToday](#getstepcountfortoday)~~
-      * ~~[getStepCountForDay](#getstepcountforday)~~
       * [getDailyStepCountSamples](#getdailystepcountsamples)
-      * ~~[getMultiDayStepCounts](#getmultidaystepcounts)~~
+      * [initStepCountObserver](#initstepcountobserver)
       * [saveSteps](#savesteps)
       * [getDistanceWalkingRunning](#getdistancewalkingrunning)
       * [getDistanceCycling](#getdistancecycling)
@@ -302,40 +300,6 @@ AppleHealthKit.getStepCount(options: Object, (err: Object, steps: Object) => {
 
 ___
 
-#### ~~**`getStepCountForToday`**~~
-**removed** - replaced by `getStepCount`
-
-get the aggregated total steps for the current day starting and ending at midnight
-```javascript
-AppleHealthKit.getStepCountForToday(null, (err: Object, steps: number) => {
-    if(this._handleHealthKitError(err, 'getStepCountForToday')){
-        return;
-    }
-    // use steps...
-});
-```
-
-___
-
-#### ~~**`getStepCountForDay`**~~
-**removed** - replaced by `getStepCount`
-
-get the the aggregated total steps for the day provided as `date` in options object. the `date` field expects an ISO date string as its value
-```javascript
-let d = new Date(2016,5,27);
-let options = {
-    date: d.toISOString()
-};
-AppleHealthKit.getStepCountForDay(options: Object, (err: Object, steps: number) => {
-    if(this._handleHealthKitError(err, 'getStepCountForDay')){
-        return;
-    }
-    // steps is the step count for day 'd'
-});
-```
-
-___
-
 #### **`getDailyStepCountSamples`**
 Get the total steps per day over a specified date range.
 
@@ -375,32 +339,69 @@ The function will be called with an array of elements. Each element is an object
 
 ___
 
-#### ~~**`getMultiDayStepCounts`**~~
-**removed** - replaced by `getDailyStepCountSamples`
+#### **`initStepCountObserver`**
+Setup an HKObserverQuery for step count (HKQuantityTypeIdentifierStepCount) that will
+trigger an event listenable on react-native `NativeAppEventEmitter` when the
+HealthKit step count has changed.
 
-Get the total steps per day over a specified date range. 
+The `initStepCountObserver` method must be called before adding a listener to
+NativeAppEventEmitter. After the step count observer has been initialized you can
+listen to the NativeAppEventEmitter `change:steps` event and re-fetch relevent
+step count data in the event handler.
+
+The `initStepCountObserver` method should be called after HealthKit has been
+successfully initialized (AppleHealthKit.initHealthKit has been called without
+error).
 
-`getMultiDayStepCounts` accepts an options object containing required *`startDate: ISO8601Timestamp`* and optional *`endDate: ISO8601Timestamp`*. if `endDate` is not provided it will default to the current time
-```javascript
-let options = {
-    startDate: (new Date(2016,5,1)).toISOString()  // required
-    endDate:   (new Date()).toISOString()          // optional; default now
-};
-```
-the function will be called with an array of elements `res` containing date and step count information
 ```javascript
- AppleHealthKit.getMultiDayStepCounts(options: Object, (err: Object, res: Array<Array<string|number>>) => {
-    if(this._handleHealthKitError(err, 'getMultiDayStepCounts')){
+// import NativeAppEventEmitter from react-native
+import {
+  Navigator,
+  View,
+  ...
+  NativeAppEventEmitter,
+} from 'react-native';
+
+...
+
+// initialize the step count observer and add an event
+// listener for 'change:steps' event after HealthKit has
+// been successfully initialized.
+AppleHealthKit.initHealthKit(HKOPTIONS, (err, res) => {
+  if(this._handleHKError(err, 'initHealthKit')){
     return;
   }
-    // 'res' is array of [ISOTimestamp: string, stepCount: number] arrays
-    // sorted ascending from startDate through endDate
-    for(let i=0; i<res.length; ++i){
-        let elem = res[i];
-        // elem[0] is ISOTimestamp : string
-        // elem[1] is step count   : number
-    }
+
+  // initialize the step count observer
+  AppleHealthKit.initStepCountObserver({}, () => {});
+
+  // add event listener for 'change:steps' and handle the
+  // event in the event handler function.
+  //
+  // when adding a listener, a 'subscription' object is
+  // returned that must be used to remove the listener
+  // when the component unmounts. The subscription object
+  // must be accessible to any function/method/instance
+  // that will be unsubscribing from the event.
+  this.sub = NativeAppEventEmitter.addListener(
+    'change:steps',
+    (evt) => {
+      // a 'change:steps' event has been received. step
+      // count data should be re-fetched from HealthKit.
+      this._fetchStepCountData();
+    }
+  );
+  ...
 });
+
+...
+
+// when the component where the listener was added unmounts
+// (or whenever the listener should be removed), call the
+// `remove` method of the subscription object.
+componentWillUnmount() {
+  this.sub.remove();
+}
 ```
 
 ___