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.
Each ViewStub
includes the android:layout
attribute to
specify the layout to inflate.
The following 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
setVisibility(View.VISIBLE)
or call
inflate()
.
Kotlin
findViewById<View>(R.id.stub_import).visibility = View.VISIBLE // or val importPanel: View = findViewById<ViewStub>(R.id.stub_import).inflate()
Java
findViewById(R.id.stub_import).setVisibility(View.VISIBLE); // or View importPanel = ((ViewStub) findViewById(R.id.stub_import)).inflate();
Note: The inflate()
method returns
the inflated View
once complete, so you don't need to call
findViewById()
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 ViewStub
.
The ID 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.