Changes

The main activity will contain a single button, the purpose of which is to create and issue an intent. Locate and load the activity_notify_demo.xml file into the Designer tool and delete the default TextView widget. Refer to the Component Tree panel and, if the parent layout is a RelativeLayout, right-click on the entry in the tree and select the Convert RelativeLayout to ConstraintLayout menu option. Accept the default settings in the resulting panel and wait for the project to rebuild.  With autoconnect enabled, drag and drop a Button object from the panel onto the center of the layout canvas as illustrated in Figure 51-5: