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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.
Define a ViewStub
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 ViewStub
simply needs to include the android:layout
attribute to
specify the layout to inflate.
The following ViewStub
is for a translucent progress bar overlay. It should
be visible only when new items are being imported into the application.
<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
visible by calling setVisibility(View.VISIBLE)
or call
inflate()
.
((ViewStub) 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/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
the one 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/inflated.)
Note: One drawback of ViewStub
is that it
doesn’t currently support the <merge/>
tag in the layouts to be inflated.