KnockoutJS - update observable from another modelview

Question

I have an existing ComposePopupView() modelview which contains observable

this.attachments = ko.observableArray([]);

and a method below

ComposePopupView.prototype.addDropboxAttachment = function (oDropboxFile)
{
    var
        oAttachment = null,
        iAttachmentSizeLimit = Utils.pInt(Settings.settingsGet('AttachmentLimit')),
        mSize = oDropboxFile['bytes']
    ;

    oAttachment = new ComposeAttachmentModel(
        oDropboxFile['link'], oDropboxFile['name'], mSize
    );

    oAttachment.fromMessage = false;
    oAttachment.cancel = this.cancelAttachmentHelper(oDropboxFile['link']);
    oAttachment.waiting(false).uploading(true).complete(false);

    this.attachments.push(oAttachment);

    this.attachmentsPlace(true);

    if (0 < mSize && 0 < iAttachmentSizeLimit && iAttachmentSizeLimit < mSize)
    {
        oAttachment.uploading(false).complete(true);
        oAttachment.error(Translator.i18n('UPLOAD/ERROR_FILE_IS_TOO_BIG'));
        return false;
    }

    Remote.composeUploadExternals(function (sResult, oData) {

        var bResult = false;
        oAttachment.uploading(false).complete(true);

        if (Enums.StorageResultType.Success === sResult && oData && oData.Result)
        {
            if (oData.Result[oAttachment.id])
            {
                bResult = true;
                oAttachment.tempName(oData.Result[oAttachment.id]);
            }
        }

        if (!bResult)
        {
            oAttachment.error(Translator.getUploadErrorDescByCode(Enums.UploadErrorCode.FileNoUploaded));
        }

    }, [oDropboxFile['link']]);

    return true;
};

Then I have created my other modelview called UsersDocumentsPopupView() where I'm accessing above method as

DropBox = __webpack_require__(/*! View/Popup/Compose */ 31)
....
DropBox.prototype.addDropboxAttachment(aFiles[0]);

but it throws an error

Cannot read property 'attachments' of undefined

Then I have decided to add observable

this.attachments = ko.observableArray([]);

to my modelview and then tired to do

this.attachment.push(oAttachment);

where oAttachment is an object taken from aFiles array but still I'm getting the same error.

My question is how or even if can I update observable attachments from one modelview executing another modelview?

PS. When I will do code below in the ComposePopupView() it works fine

var aFiles = [JSON.parse('{"isDir": false,  "name": "koala.jpg", "bytes": 780831,"link": "http://localhost/data/koala.jpg","id": "id:UxmT1S5QcFAAAAAAAAAACw"}')];

if (aFiles && aFiles[0] && aFiles[0]['link'])
{
  console.log("Test");
  self.addDropboxAttachment(aFiles[0]);
}

So in this case how can I pass data aFiles from the UsersDocumentsPopupView() to ComposePopupView() modelview?

Answer 1

attachments is a property on an instance of ComposePopupView.

addDropboxAttachment is a method on the prototype of ComposePopupView that has to be called with the this context referring to an instance of ComposePopupView in order to work.

There are several ways to solve the issue. For example:

• Most likely: you haven't created an instance yet:

  DropBox = __webpack_require__(/*! View/Popup/Compose */ 31);
  const dropBox = new DropBox();
  dropBox.addDropboxAttachment(aFiles[0]);
  

• Likely: You've already created an instance but can't access it: Pass a reference to the instance you want to refer to along in your constructors.

• Are you only going to ever create one instance of ComposePopupView? Have a look at the "Singleton" pattern. E.g.:

  // "Private" to the module
  const MySingletonClass = function() { /* ... */ }
  MySingletonClass.prototype.someMethod = function () { };
  
  let singletonInstance = null;
  
  // Only expose a way to get the instance:
  export const getSingletonInstance = function() {
    if (!singletonInstance) singletonInstance = new MySingletonClass();
    return singletonInstance;
  }
  
  // In another module:
  import { getSingletonInstance } from "./MySingletonClass";
  
  const dropBox = getSingletonInstance();
  dropBox.someMethod(aFiles[0]);
  

• Planning on creating several instances that share the attachments data? Make it a static value.

Answer 2

I have ended up to using Knockout's pub/sub functionality.

Basic example below:

var postbox = ko.observable();

function MyModalViewA()
{
    var _self = this;
    var test = new Array();
    _self.rows = ko.observableArray([]);

    postbox.subscribe(function(newValue) {         
          _self.rows.push(newValue);
          //test = test.concat(newValue);
          console.log("Rows " + JSON.stringify(test));
      }, null, "NewRowAvailable"
      );
};

function MyModalViewB()
{
    var _self = this;

    _self.search = function() {

        var newRow = JSON.parse('{ "label" : "abc" }');
        postbox.notifySubscribers(newRow, "NewRowAvailable");      
    };
};

var vma = new MyModalViewA();
ko.applyBindings(vma, $("#vma").get(0));

var vmb = new MyModalViewB();
ko.applyBindings(vmb, $("#vmb").get(0));

The first view model subscribes to a specific topic and the second view model notifies through the postbox on that topic. There is no direct dependency on each other.

Certainly the postbox would not need to be global and could be passed into the view model constructor functions or just created inside a self-executing function.

Sample: http://jsfiddle.net/xpvt214o/708647/

Also, the postbox could just be a ko.subscribable() (which is included in the ko.observable functions).