fix(ui5-toolbar): prevent flickering on item state changes

packages/main/cypress/specs/Toolbar.cy.tsx

@@ -619,4 +619,49 @@ describe("Toolbar Button", () => {
 		cy.get("ui5-toolbar-button:not([disabled])").realClick();
 		cy.get("#value-input").should("have.value", "1");
 	});
+
+	it("Should not recalculate overflow when button state changes without affecting width", () => {
+		cy.mount(
+			<Toolbar id="state-change-toolbar">
+				<ToolbarButton text="Bold" icon="bold-text"></ToolbarButton>
+				<ToolbarButton text="Italic" icon="italic-text"></ToolbarButton>
+				<ToolbarButton text="Underline" icon="underline-text"></ToolbarButton>
+				<ToolbarButton id="add-btn" text="Add" icon="add" disabled></ToolbarButton>
+				<ToolbarButton text="More" icon="employee"></ToolbarButton>
+			</Toolbar>
+		);
+
+		cy.viewport(800, 600);
+		cy.get("[ui5-toolbar]").as("toolbar");
+
+		cy.get("@toolbar")
+			.shadow()
+			.find(".ui5-tb-overflow-btn")
+			.should("have.class", "ui5-tb-overflow-btn-hidden");
+
+		cy.viewport(300, 600);
+
+		cy.get("@toolbar")
+			.shadow()
+			.find(".ui5-tb-overflow-btn")
+			.should("not.have.class", "ui5-tb-overflow-btn-hidden");
+
+		cy.get("@toolbar").then($toolbar => {
+			const toolbar = $toolbar[0] as Toolbar;
+			const addButton = document.getElementById("add-btn") as ToolbarButton;
+
+			expect(toolbar.itemsToOverflow.includes(addButton)).to.be.true;
+
+			const initialOverflowCount = toolbar.itemsToOverflow.length;
+			const initialItemsWidth = toolbar.itemsWidth;
+
+			addButton.disabled = !addButton.disabled;
+
+			cy.get("@toolbar").then($toolbarAfter => {
+				const toolbarAfter = $toolbarAfter[0] as Toolbar;
+				expect(toolbarAfter.itemsToOverflow.length).to.equal(initialOverflowCount);
+				expect(toolbarAfter.itemsWidth).to.equal(initialItemsWidth);
+			});
+		});
+	});
 });

packages/main/src/Toolbar.ts

@@ -150,8 +150,8 @@ class Toolbar extends UI5Element {
 
 	/**
 	 * Defines the items of the component.
-     *
-     * **Note:** Currently only `ui5-toolbar-button`, `ui5-toolbar-select`, `ui5-toolbar-separator` and `ui5-toolbar-spacer` are allowed here.
+	 *
+	 * **Note:** Currently only `ui5-toolbar-button`, `ui5-toolbar-select`, `ui5-toolbar-separator` and `ui5-toolbar-spacer` are allowed here.
 	 * @public
 	 */
 	@slot({
@@ -281,8 +281,11 @@ class Toolbar extends UI5Element {
 	}
 
 	onInvalidation(changeInfo: ChangeInfo) {
-		if (changeInfo.reason === "childchange" && changeInfo.child === this.itemsToOverflow[0]) {
-			this.onToolbarItemChange();
+		if (changeInfo.reason === "childchange") {
+			const currentItemsWidth = this.items.reduce((total, item) => total + this.getItemWidth(item), 0);
+			if (currentItemsWidth !== this.itemsWidth) {
+				this.onToolbarItemChange();
+			}
 		}
 	}
 
@@ -301,7 +304,7 @@ class Toolbar extends UI5Element {
 		this.storeItemsWidth();
 		this.processOverflowLayout();
 		this.items.forEach(item => {
-			 item.isOverflowed = this.overflowItems.map(overflowItem => overflowItem).indexOf(item) !== -1;
+			item.isOverflowed = this.overflowItems.map(overflowItem => overflowItem).indexOf(item) !== -1;
 		});
 	}