Angular 2 RxJS Observable Skipping Subscribe on First Call
<p>I'm using a shared service to communicate between a number of components which reside within a modal window, and I'm attempting to get a value which is set within the modal in the component within which it resides.</p>

<p>However, when I subscribe to the getSelectedSourceField function in my service, it skips over the subscribe the first time a user selects a source in the modal, but subsequent times it works as expected (i.e. returning the selected field in the success callback).</p>

<p>Any thoughts?</p>

<p>My service:</p>

<pre><code>import { Injectable } from '@angular/core';
import { Subject } from 'rxjs/Subject';
import { Observable } from 'rxjs/Observable';
import { Source, SourceField } from '../source/source';
import { DataService } from './dataService';

@Injectable()
export class SFieldSelectService {
private selectedSource: Source = null;
private selectedSourceField: SourceField = null;
private filteredSourceFields: SourceField[] = [];

private selectedSourceSubj = new Subject&lt;Source&gt;();
private selectedSourceFieldSubj = new Subject&lt;SourceField&gt;();
private filteredSourceFieldsSubj = new Subject&lt;SourceField[]&gt;();
private hasSourceFieldSubj = new Subject&lt;boolean&gt;();

//Source methods
setSelectedSource(source: Source) {
    this.selectedSource = source;
    this.selectedSourceSubj.next(source);

    //Set the availabel source fields
    this._dataService.GetSingle('SourceSelect', this.selectedSource["sourceId"])
        .subscribe(sourceFields =&gt; {
            this.filteredSourceFields = sourceFields
            this.filteredSourceFieldsSubj.next(sourceFields);
        });   

    this.hasSourceFieldSubj.next(false);
}
getSelectedSource(): Observable&lt;Source&gt; {
    return this.selectedSourceSubj.asObservable();
}

//Sourcefield methods
setSelectedSourceField(sourceField: SourceField) {
    this.selectedSourceField = sourceField;
    this.selectedSourceFieldSubj.next(sourceField);

    this.hasSourceFieldSubj.next(true);
}
getSelectedSourceField(): Observable&lt;SourceField&gt; {
    return this.selectedSourceFieldSubj.asObservable();
}

//Filtered sourcefields
getFilteredSourceFields(): Observable&lt;SourceField[]&gt; {
    return this.filteredSourceFieldsSubj.asObservable();
}

//Whether or not the modal has a selected sourcefield
hasSelectedSourceField(): Observable&lt;boolean&gt; {
    return this.hasSourceFieldSubj.asObservable();
}

constructor(private _dataService: DataService) {}
}
</code></pre>

<p>Component where I'm subscribing:</p>

<pre><code>import { Component, ViewChild, OnInit } from '@angular/core';
import { DataService } from '../../services/dataService';
import { Response, Headers } from '@angular/http';
import { Condition } from '../transformation';
import { NgbModal, ModalDismissReasons } from '@ng-bootstrap/ng-bootstrap';
import { SourceFieldListComponent } from '../../source/selection/sourcefield-list.component';
import { SourceListComponent } from '../../source/selection/source-list.component';
import { SFieldSelectService } from '../../services/source-select.service';

@Component({
    selector: 'condition-addedit',
    templateUrl: 'app/transformation/condition/condition-addedit.component.html',
    providers: [DataService, SFieldSelectService]
})
export class ConditionAddEditComponent implements OnInit {
    active: boolean = true;
    condSeqCount = 1;
    selectingCondition: Condition;
    hasSelectedSourceField: boolean = false;

    //List of Conditions currently in the add/edit list
    public conditions: Condition[] = [];

    //Modal Functions
    closeResult: string;
    openSourceSelect(content, condition) {
        this.selectingCondition = condition;
        this.modalService.open(content, { size: 'lg' }).result.then((result) =&gt; {
            //User selected source field in modal
            if (result == 'Select SField') {
                this.selectService.getSelectedSourceField()
                    .subscribe(sourceField =&gt; { &lt;--- SKIPS THIS THE FIRST TIME BUT NOT AFTER
                        alert(sourceField.name);
                        this.selectingCondition.sourceField = sourceField
                    }
                , (error) =&gt; alert(error));
            }
        }, (reason) =&gt; {
            this.closeResult = `Dismissed ${this.getDismissReason(reason)}`;
        });
    }

    private getDismissReason(reason: any): string {
        if (reason === ModalDismissReasons.ESC) {
            return 'by pressing ESC';
        } else if (reason === ModalDismissReasons.BACKDROP_CLICK) {
            return 'by clicking on a backdrop';
        } else {
            return `with: ${reason}`;
        }
    }

    //Add a new condition to the list of conditions
    addCondition() {
        this.conditions.push(new Condition(this.condSeqCount++, (this.condSeqCount == 1) ? '' : 'or', '', '', '', '', null));
    }

    constructor(private _dataService: DataService, private modalService: NgbModal, private selectService: SFieldSelectService) {}
    ngOnInit(): void {
        this.selectService.hasSelectedSourceField().subscribe(hasSelectedSourceField =&gt; this.hasSelectedSourceField = hasSelectedSourceField);
    }
}
</code></pre>