Sometimes your layout might require complex views that are rarely used. Whether they are item details, progress indicators, or undo messages, you can reduce memory usage and speed up rendering by loading the views only when they are needed.
Deferring loading resources is an important technique to use when you have complex views that
your app might need in the future. You can implement this technique by defining a
ViewStub for those complex and rarely used views.
Define a ViewStub
ViewStub is a lightweight view with no dimension that doesn’t draw anything
or participate in the layout. As such, it's cheap to inflate and cheap to leave in a view hierarchy.
ViewStub simply needs to include the
android:layout attribute to
specify the layout to inflate.
ViewStub is for a translucent progress bar overlay. It should
be visible only when new items are being imported into the app.
<ViewStub android:id="@+id/stub_import" android:inflatedId="@+id/panel_import" android:layout="@layout/progress_overlay" android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_gravity="bottom" />
Load the ViewStub Layout
findViewById<View>(R.id.stub_import).visibility = View.VISIBLE // or val importPanel: View = findViewById<ViewStub>(R.id.stub_import).inflate()
findViewById(R.id.stub_import).setVisibility(View.VISIBLE); // or View importPanel = ((ViewStub) findViewById(R.id.stub_import)).inflate();
Once visible/inflated, the
ViewStub element is no longer part of the view
hierarchy. It is replaced by the inflated layout and the ID for the root view of that layout is
the one specified by the
android:inflatedId attribute of the ViewStub. (The ID
android:id specified for the
ViewStub is valid only until the
ViewStub layout is visible/inflated.)
Note: One drawback of
ViewStub is that it
doesn’t currently support the
<merge> tag in the layouts to be inflated.
For additional information on this topic, see Optimize with stubs (blog post).