Load views on demand

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.

    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().


findViewById<View>(R.id.stub_import).visibility = View.VISIBLE
// or
val importPanel: View = findViewById<ViewStub>(R.id.stub_import).inflate()


// 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.