Preview

Not Found page with Back button

Coding

You can view and download all files in the Samples in the Demo Kit at Routing and Navigation - Step 4.

webapp/view/NotFound.view.xml

<mvc:View
	controllerName="sap.ui.demo.nav.controller.NotFound"
	xmlns="sap.m"
	xmlns:mvc="sap.ui.core.mvc">
	<MessagePage
		title="{i18n>NotFound}"
		text="{i18n>NotFound.text}"
		description="{i18n>NotFound.description}"
		showNavButton="true"
		navButtonPress="onNavBack"/>
</mvc:View>

In the NotFound view, we set the property showNavButton of the MessagePage control to true to automatically display the Back button. We also add an event handler function onNavBack to the navButtonPress event of the control. The onNavBack function will handle the actual back navigation. We could directly add this function to the view’s controller. However, we are smart enough to anticipate that we might need the same handler function for different views. DRY (Don’t Repeat Yourself) is the right approach for us, so let’s create a BaseController from which all other controllers will inherit.

webapp/controller/BaseController.js (New)

sap.ui.define([
	"sap/ui/core/mvc/Controller",
	"sap/ui/core/routing/History",
	"sap/ui/core/UIComponent"
], function(Controller, History, UIComponent) {
	"use strict";

	return Controller.extend("sap.ui.demo.nav.controller.BaseController", {

		getRouter : function () {
			return UIComponent.getRouterFor(this);
		},

		onNavBack: function () {
			var oHistory, sPreviousHash;

			oHistory = History.getInstance();
			sPreviousHash = oHistory.getPreviousHash();

			if (sPreviousHash !== undefined) {
				window.history.go(-1);
			} else {
				this.getRouter().navTo("appHome", {}, true /*no history*/);
			}
		}

	});

});

Create a new BaseController.js file in the webapp/controller folder. The base controller implements a set of functions that are reused by its subclasses. The onNavBack handler is a great example of code that we don’t want to duplicate in our controllers for each page that has a back navigation.

The function checks if there is a previous hash value in the app history. If so, it redirects to the previous hash via the browser’s native History API. In case there is no previous hash we simply use the router to navigate to the route appHome which is our home view.

The third parameter of navTo("appHome", {}, true /*no history*/); has the value true and makes sure that the hash is replaced. With the line sap.ui.core.UIComponent.getRouterFor(this) you can easily access your component’s router throughout the app. To make it even more comfortable, we also add a handy shortcut getRouter to the base controller. This function is now available in each subclass as well. It is also used in the onNavBack handler to get a reference to the router before calling navTo. We now have to implement the reuse in all other controllers.

webapp/controller/NotFound.controller.js

sap.ui.define([
	"sap/ui/demo/nav/controller/BaseController"

], function (BaseController) {
	"use strict";
	return BaseController.extend("sap.ui.demo.nav.controller.NotFound", {
		onInit: function () {
		}
	});
});

In order to reuse the base controller implementation, we have to change the dependency from sap/ui/core/mvc/Controller to sap/ui/demo/nav/controller/BaseController and directly extend the base controller.

At this point you can open index.html#/thisIsInvalid in your browser and press the Back button to see what happens. You will be redirected to the app’s home page that is matched by the route appHome as you opened the Not Found page with an invalid hash. If you change the hash to something invalid when you are on the home page of the app, you will also go to the Not Found page but with a history entry. When you press back, you will get to the home page again, but this time with a native history navigation.

webapp/controller/App.controller.js

sap.ui.define([
	"sap/ui/demo/nav/controller/BaseController"

], function (BaseController) {
	"use strict";
	return BaseController.extend("sap.ui.demo.nav.controller.App", {
		onInit: function () {
		}
	});
});

To be consistent, we will now extend all of our controllers with the base controller. Change the app controller as described above.

webapp/controller/Home.controller.js

sap.ui.define([
	"sap/ui/demo/nav/controller/BaseController"

], function (BaseController) {
	"use strict";
	return BaseController.extend("sap.ui.demo.nav.controller.Home", {
	});
});

The same applies to our home controller, we also extend it with the base controller now.

Conventions

• Implement a global onNavBack handler for back navigation in your app

• Query the history and go to the home page if there is no history available for the current app