A layout defines the user interface of an activity or an app widget. Layouts are declared in XML resource definition files. See the topic Creating Resources to find out how to create resource folders and resource definition files.
This functionality at the IntelliJ IDEA level is provided through the Android Designer bundled plugin, which is by default enabled. If not, enable it in the Plugin Configuration Wizard or the Plugins page of the Settings dialog box.
You can toggle between these modes by switching between the Design and Text tabs in the editor where the layout definition file is opened.
Just keep in mind, that the set of available panes and tool windows depends on the current layout editing mode: the Designer tool window with its panes is available in the Design mode, while the Preview tool window is available in the Text mode. However, most of the
In the Design mode, you can switch to the manual mode by choosing Go to Declaration on the context menu of the Design pane.