UI: Fix widget labels pattern processing.

ui-ngx/src/app/core/api/widget-api.models.ts

@@ -284,6 +284,8 @@ export interface IWidgetSubscription {
 
   legendData: LegendData;
 
+  readonly firstDatasource?: Datasource;
+
   datasourcePages?: PageData<Datasource>[];
   dataPages?: PageData<Array<DatasourceData>>[];
   datasources?: Array<Datasource>;

ui-ngx/src/app/core/api/widget-subscription.ts

@@ -160,6 +160,16 @@ export class WidgetSubscription implements IWidgetSubscription {
   warnOnPageDataOverflow: boolean;
   ignoreDataUpdateOnIntervalTick: boolean;
 
+  get firstDatasource(): Datasource {
+    if (this.type === widgetType.alarm) {
+      return this.alarmSource;
+    } else if (this.datasources?.length) {
+      return this.datasources[0];
+    } else {
+      return null;
+    }
+  }
+
   datasourcePages: PageData<Datasource>[];
   dataPages: PageData<Array<DatasourceData>>[];
   entityDataListeners: Array<EntityDataListener>;

ui-ngx/src/app/modules/home/models/widget-component.models.ts

@@ -477,8 +477,9 @@ export class LabelVariablePattern {
 
   update() {
     let label = this.pattern;
-    if (this.hasVariables && this.ctx.defaultSubscription?.datasources?.length) {
+    const datasource = this.ctx.defaultSubscription?.firstDatasource;
-      label = createLabelFromDatasource(this.ctx.defaultSubscription.datasources[0], label);
+    if (this.hasVariables && datasource) {
+      label = createLabelFromDatasource(datasource, label);
     }
     if (this.labelSubject.value !== label) {
       this.labelSubject.next(label);