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      1 page.title=Loading Views On Demand
      2 parent.title=Improving Layout Performance
      3 parent.link=index.html
      4 
      5 trainingnavtop=true
      6 previous.title=Re-using Layouts with <include/>
      7 previous.link=reusing-layouts.html
      8 next.title=Making ListView Scrolling Smooth
      9 next.link=smooth-scrolling.html
     10 
     11 @jd:body
     12 
     13 
     14 <div id="tb-wrapper">
     15 <div id="tb">
     16 
     17 <!-- table of contents -->
     18 <h2>This lesson teaches you to</h2>
     19 <ol>
     20   <li><a href="#ViewStub">Define a ViewStub</a></li>
     21   <li><a href="#Load">Load the ViewStub Layout</a></li>
     22 </ol>
     23 
     24 <!-- other docs (NOT javadocs) -->
     25 <h2>You should also read</h2>
     26 <ul>
     27   <li><a href="{@docRoot}resources/articles/layout-tricks-stubs.html">Using ViewStubs</a></li>
     28 </ul>
     29 
     30 </div>
     31 </div>
     32 
     33 
     34 <p>Sometimes your layout might require complex views that are rarely used. Whether
     35 they are item details, progress indicators, or undo messages, you can reduce memory usage and speed
     36 up rendering by loading the views only when they are needed.</p>
     37 
     38 
     39 <h2 id="ViewStub">Define a ViewStub</h2>
     40 
     41 <p>{@link android.view.ViewStub} is a lightweight view with no dimension and doesnt draw anything
     42 or participate in the layout. As such, it's cheap to inflate and cheap to leave in a view hierarchy.
     43 Each {@link android.view.ViewStub} simply needs to include the {@code android:layout} attribute to
     44 specify the layout to inflate.</p>
     45 
     46 <p>The following {@link android.view.ViewStub} is for a translucent progress bar overlay. It should
     47 be visible only when new items are being imported into the application.</p>
     48 
     49 <pre>
     50 &lt;ViewStub
     51     android:id="@+id/stub_import"
     52     android:inflatedId="@+id/panel_import"
     53     android:layout="@layout/progress_overlay"
     54     android:layout_width="fill_parent"
     55     android:layout_height="wrap_content"
     56     android:layout_gravity="bottom" /&gt;
     57 </pre>
     58 
     59 
     60 <h2 id="Load">Load the ViewStub Layout</h2>
     61 
     62 <p>When you want to load the layout specified by the {@link android.view.ViewStub}, either set it
     63 visible by calling {@link android.view.View#setVisibility setVisibility(View.VISIBLE)} or call
     64 {@link android.view.ViewStub#inflate()}.</p>
     65 
     66 <pre>
     67 ((ViewStub) findViewById(R.id.stub_import)).setVisibility(View.VISIBLE);
     68 // or
     69 View importPanel = ((ViewStub) findViewById(R.id.stub_import)).inflate();
     70 </pre>
     71 
     72 <p class="note"><strong>Note:</strong> The {@link android.view.ViewStub#inflate()} method returns
     73 the inflated {@link android.view.View} once complete. so you don't need to call {@link
     74 android.app.Activity#findViewById findViewById()} if you need to interact with the layout.</p>
     75 
     76 <p>Once visible/inflated, the {@link android.view.ViewStub} element is no longer part of the view
     77 hierarchy. It is replaced by the inflated layout and the ID for the root view of that layout is
     78 the one specified by the {@code android:inflatedId} attribute of the ViewStub. (The ID {@code
     79 android:id} specified for the {@link android.view.ViewStub} is valid only until the {@link
     80 android.view.ViewStub} layout is visible/inflated.)</p>
     81 
     82 <p class="note"><strong>Note:</strong> One drawback of {@link android.view.ViewStub} is that it
     83 doesnt currently support the {@code &lt;merge/&gt;} tag in the layouts to be inflated.</p>
     84 
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