LWC Get Pick-list Field Values

LWC does have a wire adapter that pulls in picklist values dynamically.

import { LightningElement, wire, track } from 'lwc';
import { getPicklistValues } from 'lightning/uiObjectInfoApi';
import INDUSTRY_FIELD from '@salesforce/schema/Account.Industry';
import {getRecord, getFieldValue} from 'lightning/uiRecordApi';

const fields = [INDUSTRY_FIELD];

export default class Example extends LightningElement {
    @api recordId;
    @track selectedOption; 
    @track options;

   /*
    * There is no guarantee that the pick-list values will return first
    * Because of this, we check to see if a selected option already exists
    * If it does, we verify it is a valid value for the picklist.
    * If it is not valid, we set the selected option to the default value.
    * If it is valid, no changes are made
    * If there is no selected option, we use the default option
    *
    * Note: recordTypeId is required. If your object has no record types create
    * at least 1.
    */
    @wire(getPicklistValues, { recordTypeId: '012000000000000AAA', fieldApiName: INDUSTRY_FIELD })
    setPicklistOptions({error, data}) {
        if (data) {
            this.options = data.values;

            if (this.selectedOption) {
                let optionIsValid = this.options.some(function(item) {
                    return item.value === this.selectedOption;
                }, this);

                if (!optionIsValid) {
                    this.selectedOption = data.defaultValue;
                }
            } else {
                this.selectedOption = data.defaultValue;
            }
        } else if (error) {
            console.log(error);
        }
    }


    /*
     * As with above, there is no guarantee to which order these functions execute
     * If the options list exists, we will check to see if our value is valid.
     * If it is, set our value as the selected value
     * If it is not, do nothing
     * If the options list does not exist, we will create an options list with 
     *   a single value using this records picklist value.
     */
    @wire(getRecord, {recordId:'$recordId', fields})
    account({error, data}) {
        if (data) {
            let industryValue = getFieldValue(data, INDUSTRY_FIELD);

            if (!this.options) {
                this.options = [{label:industryValue, value:industryValue}];
            }

            let industryIsValid = options.some(function(item) {
                return item.value === industryValue;
            }, this);

            if (industryIsValid) {
                this.selectedOption = industryValue;
            }
        } else if (error) {
            console.log(error);
        }
    }
}

I had some free time this morning, and this is how you can control wire adapter run order. I misspoke earlier about requiring usage of use getter/setters, the important bit is actually how you forcefully (re)invoke the wire.

Wires are invoked based on some kind of change (the reactive part) and a null to truthy change is perfectly valid way to (re)invoke it.

If you inspect both error and data when supplied with a falsey / undefined reactive var when the component is constructed, both come back undefined and it fails silently (this is good).

However, something like this will (re)invoke a wire adapter:

<template>
  <lightning-combobox
    label="Example"
    value={selectedOption}
    options={options}
  ></lightning-combobox>
</template>

import { LightningElement, api, wire, track } from 'lwc';
import { getPicklistValues } from 'lightning/uiObjectInfoApi';
import TYPE_FIELD from '@salesforce/schema/Account.Type';
import { getRecord, getFieldValue } from 'lightning/uiRecordApi';

const fields = [TYPE_FIELD];

export default class Example extends LightningElement {
  @api recordId;
  @track selectedOption;
  @track options;

  // private
  _recordTypeId;

  // Step 1
  @wire(getRecord, {recordId:'$recordId', fields})
  account({error, data}) {
    if (data) {
      let typeValue = getFieldValue(data, TYPE_FIELD);
      this.selectedOption = typeValue;
      this._recordTypeId = '012000000000000AAA'; // setting this value will re-invoke the wire
    } else if (error) {
      console.log(error);
    }
  }

  // Step 2, determined by when the reactive bind is changed
  @wire(getPicklistValues, { recordTypeId: '$_recordTypeId', fieldApiName: TYPE_FIELD })
  setPicklistOptions({error, data}) {
    if (data) {
      // Apparently combobox doesn't like it if you dont supply any options at all.
      // Even though selectedOption was assigned in step 1, it wont "select" it unless it also has options
      this.options = data.values;
    } else if (error) {
      console.log(error);
    }
  }

}