Lightning PageReference Object Passing Field Values in standard__object

Question

I am launching a Subtab using the Lightning Workspace API, and using an Aura pageReference object to specify that I want to create a new Task.

I want to pre-populate the WhatId on the Task when the new standard__object tab opens.

I set the WhatId in the state I want to pass into the pageReference object:

var workspaceAPI = component.find("workspace");
var recordId = component.get("v.recordId") // confirmed this is my intended WhatId recordId
workspaceAPI.getEnclosingTabId().then(function(enclosingTabId) {
    workspaceAPI.openSubtab({
            parentTabId: enclosingTabId,
            pageReference: 
            {    
                "type": "standard__objectPage",
                "attributes": {
                    "objectApiName": "Task",
                    "actionName": "new"
                },
                "state": {
                    "WhatId": recordId
                }
            }
        }).then(function(subtabId) {
            console.log("The new subtab ID is:" + subtabId);
        }).catch(function(error) {
            console.log("error");
        });
    })
.catch(function(error) {
    console.log(error);
});

But it doesn't appear to be passing the input as a query parameter - and when the new record lightning component opens in the subtab the Related: input field is blank.

Answer 1

I figured out the appropriate answer is to use the force:createRecord event:

var createRecordEvent = $A.get("e.force:createRecord");
createRecordEvent.setParams({
    "entityApiName": "Task",
    "defaultFieldValues": {
         // "WhatId": 
    }
});
createRecordEvent.fire();

Also, it appears that when fired from within a subtab this event will open a new subtab, I am not sure if it works the other way around.