Sometimes your layout requires 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're needed.
You can defer loading resources when you have complex views that
your app needs in the future by defining a
ViewStub for 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 requires few resources to inflate and leave in a view hierarchy.
ViewStub includes the
android:layout attribute to
specify the layout to inflate.
ViewStub is for a translucent progress bar overlay. It's only
visible 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
When you want to load the layout specified by the
ViewStub, either set it to
visible by calling
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();
inflate() method returns
View once complete, so you don't need to call
if you need to interact with the layout.
Once visible or 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
specified by the
android:inflatedId attribute of the
android:id specified for the
ViewStub is valid only until the
ViewStub layout is visible or inflated.
Note: A 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.