Click the tab for the layout file, activity_main.xml. This will open the layout editor in the editor tool window (Figure 1.9). If you do not see a tab for activity_main.xml, do not worry. Expand app/res/layout/ in the project tool window. Double-click activity_main.xml to open the file. If activity_main.xml opens but shows XML instead of the layout editor, click the Design tab at the bottom of the editor tool window.
Figure 1.9 Layout editor
By convention, a layout file is named based on the activity it is associated with:
Its name begins with
activity_, and the rest of the activity name follows in all ...