<!DOCTYPE html>
<html style="height: 100%;">
  <head>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Demo</title>
    <script id="sap-ui-bootstrap"
      src="https://openui5.hana.ondemand.com/resources/sap-ui-core.js"
      data-sap-ui-theme="sap_fiori_3"
      data-sap-ui-async="true"
      data-sap-ui-oninit="module:sap/ui/core/ComponentSupport"
      data-sap-ui-compatversion="edge"
      data-sap-ui-excludejquerycompat="true"
      data-sap-ui-resourceroots='{ "demo": "./" }'
      data-sap-ui-xx-waitfortheme="init"
    ></script>
  </head>
  <body id="content" class="sapUiBody">
    <div style="height: 100%;"
      data-sap-ui-component
      data-id="rootComponentContainer"
      data-name="demo"
      data-height="100%"
      data-settings='{ "id": "rootComponent" }'
    ></div>
  </body>
</html>
sap.ui.define([
  "sap/ui/core/UIComponent",
  "sap/ui/model/json/JSONModel",
  "sap/ui/Device",
], function(UIComponent, SampleModel, Device) {
  "use strict";

  return UIComponent.extend("demo.Component", {
    metadata: {
      manifest: "json",
    },

    init: function() {
      UIComponent.prototype.init.apply(this, arguments);
      this.setDensity().setModel(new SampleModel({
        myItems: [
          {
            itemText: "123"
          },
          {
            itemText: "abc"
          },
          {
            itemText: 456
          },
        ]
      }));
    },

    setDensity: function({
      styleClass = Device.system.desktop ? "sapUiSizeCompact" : "sapUiSizeCozy",
      targetElement = document.body,
    } = {}) {
      targetElement.classList.add(styleClass);
      return this;
    },

  });
});
{
  "_version": "1.25.0",
  "start_url": "index.html",
  "sap.app": {
    "id": "demo",
    "type": "application",
    "title": "App Title",
    "description": "Sample Code",
    "applicationVersion": {
      "version": "1.0.0"
    },
    "dataSources": {

    }
  },
  "sap.ui": {
    "technology": "UI5",
    "deviceTypes": {
      "desktop": true,
      "tablet": true,
      "phone": true
    }
  },
  "sap.ui5": {
    "dependencies": {
      "minUI5Version": "1.58.0",
      "libs": {
        "sap.ui.core": {},
        "sap.m": {},
        "sap.ui.layout": {}
      }
    },
    "contentDensities": {
      "compact": true,
      "cozy": true
    },
    "resources": {
      "js": [
        
      ],
      "css": [
        
      ]
    },
    "models": {

    },
    "rootView": {
      "viewName": "demo.view.App",
      "id": "rootView",
      "type": "XML",
      "async": true
    }
  }
}
<mvc:View
  xmlns:mvc="sap.ui.core.mvc"
  xmlns="sap.m"
  xmlns:core="sap.ui.core"
  xmlns:layout="sap.ui.layout"
  xmlns:my="demo.control"
  displayBlock="true"
  height="100%"
>
  <App id="rootApp" autoFocus="false">
    <Page showHeader="false" class="sapUiResponsiveContentPadding">
      <layout:HorizontalLayout allowWrapping="true">
        <!--Try also other container such as sap.m.HBox w/ renderType="Bare"-->
        <my:LabelComboBox
          required="true"
          placeholder="Placeholder"
          text="My awesome label"
        >
          <core:Item text="Item 1" key="key1" />
          <core:Item text="Item 2" key="key2" />
          <core:Item text="Item 3" key="key3" />
        </my:LabelComboBox>
        <my:LabelComboBox
          placeholder="With binding"
          items="{/myItems}"
          text="My awesome suuuuuuuuuuuuuuuuuuuuuuuuuuuuper long text"
        >
          <core:Item text="{itemText}" />
        </my:LabelComboBox>
      </layout:HorizontalLayout >
    </Page>
  </App>
</mvc:View>
sap.ui.define([
  "sap/ui/core/XMLComposite",
], function(XMLComposite) {
  "use strict";

  /**
   * MINIMAL SAMPLE
   */
  return XMLComposite.extend("demo.control.LabelComboBox", {
    // No renderer required.
    metadata: {
      properties: {
        "text": {
          type: "string",
          bindable: true,
        },
        "required": {
          type: "boolean",
          bindable: true,
        },
        "placeholder": {
          type: "string",
          bindable: true,
        },
        "width": {
          type: "sap.ui.core.CSSSize",
          bindable: true,
          defaultValue: "100%"
        },
      },
      aggregations: {
        "items": {
          type: "sap.ui.core.Item",
          multiple: true,
          bindable: true,
          forwarding: {
            idSuffix: "--innerComboBox",
            aggregation: "items",
            forwardBinding: true,
          }
        }
      },
      defaultAggregation: "items",
    },

    onThemeChanged: function() {
      alert("Theme changed")
    }

  });
});
<core:FragmentDefinition xmlns:core="sap.ui.core" xmlns="sap.m">
  <HBox id="containerBox"
    alignItems="Baseline"
    width="{$this>width}"
    renderType="Bare"
    wrap="Wrap"
  >
    <Label id="innerLabel"
      required="{$this>required}"
      text="{$this>text}:"
      labelFor="innerComboBox"
      wrapping="true"
      wrappingType="Hyphenated"
      class="sapUiTinyMarginEnd"
    >
      <layoutData>
        <FlexItemData alignSelf="Center" />
      </layoutData>
    </Label>
    <ComboBox id="innerComboBox" placeholder="{$this>placeholder}">
      <layoutData>
        <FlexItemData growFactor="1" />
      </layoutData>
    </ComboBox>
  </HBox>
</core:FragmentDefinition>