I have developed an Ionic 3 application that utilizes NGRX for state management purposes. The app is designed to connect to a device via BLE technology.
Within my connection page, where the BLE device is connected, I have implemented the following code:
private connectionStateChangedCount: number;
constructor(public navCtrl: NavController,
public navParams: NavParams,
private device: DeviceActionsDispatcherProvider) {
this.connectionStateChangedCount = 0;
console.log('CONNECTION - constructor ' + this.connectionStateChangedCount);
store.select(s => s.connection).subscribe(this.connectionStateChanged.bind(this));
}
// To ensure that this.device.onConnection() is only called once when the deviceConnectionState is “connected"
connectionStateChanged(connectionStore: any) {
if (connectionStore.deviceConnectionState === 'connected' &&
this.connectionStateChangedCount === 0) {
this.connectionStateChangedCount = this.connectionStateChangedCount + 1;
console.log('CONNECTION – connectionStateChanged ' + this.connectionStateChangedCount);
this.device.onConnection();
}
}
Occasionally, in chrome://inspect, the following output is observed:
connection.ts:67 CONNECTION – connectionStateChanged 1
connection.ts:67 'CONNECTION – connectionStateChanged 1
The scenario where 'CONNECTION – connectionStateChangedCount is incremented but the subscription function connectionStateChanged is called twice with connectionStateChangedCount being 1 in both instances, back-to-back, raises confusion.
An attempt was made to replace the variable connectionStateChangedCount with an unsubscribe in the if statement as a mitigation strategy to avoid additional calls to this.device.onConnection(). This solution proved unsuccessful as occasional occurrences of two calls persisted.
Additional observations include:
- There are no multiple calls to the connection page constructor during these incidents.
- This issue arises when disconnecting from the BLE device, navigating to ConnectionPage using this.nav.setRoot(ConnectionPage) in app.component.ts, and attempting to reconnect to the BLE device on the root ConnectionPage.
Insights or suggestions on why this phenomenon is happening would be greatly appreciated.