page.title=Loading Views On Demand parent.title=Improving Layout Performance parent.link=index.html trainingnavtop=true previous.title=Re-using Layouts with <include/> previous.link=reusing-layouts.html next.title=Making ListView Scrolling Smooth next.link=smooth-scrolling.html @jd:body <div id="tb-wrapper"> <div id="tb"> <!-- table of contents --> <h2>This lesson teaches you to</h2> <ol> <li><a href="#ViewStub">Define a ViewStub</a></li> <li><a href="#Load">Load the ViewStub Layout</a></li> </ol> <!-- other docs (NOT javadocs) --> <h2>You should also read</h2> <ul> <li><a href="http://android-developers.blogspot.com/2009/03/android-layout-tricks-3-optimize-with.html" >Optimize with stubs (blog post)</a></li> </ul> </div> </div> <p>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.</p> <h2 id="ViewStub">Define a ViewStub</h2> <p>{@link android.view.ViewStub} is a lightweight view with no dimension and doesn’t draw anything or participate in the layout. As such, it's cheap to inflate and cheap to leave in a view hierarchy. Each {@link android.view.ViewStub} simply needs to include the {@code android:layout} attribute to specify the layout to inflate.</p> <p>The following {@link android.view.ViewStub} is for a translucent progress bar overlay. It should be visible only when new items are being imported into the application.</p> <pre> <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" /> </pre> <h2 id="Load">Load the ViewStub Layout</h2> <p>When you want to load the layout specified by the {@link android.view.ViewStub}, either set it visible by calling {@link android.view.View#setVisibility setVisibility(View.VISIBLE)} or call {@link android.view.ViewStub#inflate()}.</p> <pre> ((ViewStub) findViewById(R.id.stub_import)).setVisibility(View.VISIBLE); // or View importPanel = ((ViewStub) findViewById(R.id.stub_import)).inflate(); </pre> <p class="note"><strong>Note:</strong> The {@link android.view.ViewStub#inflate()} method returns the inflated {@link android.view.View} once complete. so you don't need to call {@link android.app.Activity#findViewById findViewById()} if you need to interact with the layout.</p> <p>Once visible/inflated, the {@link android.view.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 {@code android:inflatedId} attribute of the ViewStub. (The ID {@code android:id} specified for the {@link android.view.ViewStub} is valid only until the {@link android.view.ViewStub} layout is visible/inflated.)</p> <p class="note"><strong>Note:</strong> One drawback of {@link android.view.ViewStub} is that it doesn’t currently support the {@code <merge>} tag in the layouts to be inflated.</p>