How a gradient can be applied to the Toolbar but only when it is extended if it belongs within a CollapsingToolbarLayout .
That is, I have a Toolbar that below it an image is displayed, which expands to the Statusbar and I want to highlight the controls that are shown above the image, the guide of Google Material Design style says you should use a gradient, dark to transparent.
I have solved by overlaying the gradient on top of the image using a RelativeLayout
Before
After
<android.support.design.widget.AppBarLayout
android:id="@+id/app_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fitsSystemWindows="true"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">
<android.support.design.widget.CollapsingToolbarLayout
android:id="@+id/collapsing_toolbar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:fitsSystemWindows="true"
app:contentScrim="?attr/colorPrimary"
app:layout_scrollFlags="scroll|exitUntilCollapsed|snap"
app:titleEnabled="true">
<RelativeLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:fitsSystemWindows="true"
app:layout_collapseMode="parallax">
<ImageView
android:id="@+id/image_header"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:background="@drawable/about_background_header"
android:contentDescription="@string/desc_empty"
android:fitsSystemWindows="true"
android:scaleType="centerCrop" />
<View
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@drawable/scrim_top_linear" />
</RelativeLayout>
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:layout_collapseMode="pin"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>
Resource for gradient scrim_top_linear.xml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle" >
<gradient
android:type="linear"
android:centerX="40%"
android:startColor="#99000000"
android:centerColor="#00474747"
android:endColor="#00000000"
android:angle="270"/>
</shape>