A small android library for tagging views inside a ScrollView as "sticky" making them stick to the top of the scroll container until a new sticky view comes and takes it's place
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StickyScrollViewItems

StickyScrollViewItems is a ScrollView subclass that allowed you to mark items inside the ScrollView as sticky. The items marked as sticky will stick to the top of the ScrollView until another sticky items comes by and pushes it out of the way.

Installing

Add the following gradle dependency exchanging x.x.x for the latest release.

dependencies {
    compile 'se.emilsjolander:StickyScrollViewItems:x.x.x'
}

Usage

First of all replace any instance of ScrollView with StickyScrollView. So you go from this:

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
	android:layout_height="match_parent" android:layout_width="match_parent">
	<!-- scroll view child goes here -->
</ScrollView>

to this:

<StickyScrollView xmlns:android="http://schemas.android.com/apk/res/android"
	android:layout_height="match_parent" android:layout_width="match_parent"
	android:id="@+id/sticky_scroll">
	<!-- scroll view child goes here -->
</StickyScrollView>

As with a regular ScrollView you are only allowed one child. But that child can contain any number of children. It is these children or any of their children that can be tagged as a sticky view. If you want t view to stick to the top when you scroll passed it add a sticky tag with the android:tag attribute to it like this:

<StickyScrollView xmlns:android="http://schemas.android.com/apk/res/android"
	android:id="@+id/sticky_scroll"
	android:layout_height="match_parent" android:layout_width="match_parent">

	<LinearLayout 
		android:layout_height="match_parent" android:layout_width="match_parent" 
		android:orientation="horizontal">

		<!-- other children -->

		<View 
			android:layout_height="300dp" 
			android:layout_width="match_parent"
			android:tag="sticky"/>

		<!-- other children -->

	</LinearLayout>

</StickyScrollView>

There are also two additional flags that can be set on views that were added to optimize performance for the most usual cases. If the view you want to stick either has transparency or does not have a constant representation than you must supply one or both of the following flags. -hastransparancy for views that have transparancy and -nonconstant for views that will change appearance during there sticky time (examples are buttons with pressed states as well as progress spinners).

So this ends up with 4 different ways to tag a view as sticky resulting is slightly different behaviour android:tag="sticky" android:tag="sticky-hastransparancy" android:tag="sticky-nonconstant" and android:tag="sticky-hastransparancy-nonconstant".

If you want to add a shadow drawable below the stuck items, you must declare a namespace to find the shadow attributes xmlns:whatever="http://schemas.android.com/apk/res-auto". Usually you do this in the root layout element in you layout.xml file. You can then specify the shadow drawable with whatever:stuckShadowDrawable="" and the shadow height with whatever:stuckShadowHeight="" in xml. Note that when left unspecified, the default shadow height is 10dip.

<StickyScrollView xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:whatever="http://schemas.android.com/apk/res-auto"
  android:layout_height="match_parent" android:layout_width="match_parent"
  android:id="@+id/sticky_scroll"
  whatever:stuckShadowDrawable="@drawable/sticky_shadow_default"
  whatever:stuckShadowHeight="50dip" >
  <!-- scroll view child goes here -->
</StickyScrollView>

These shadow height and drawable can also be set programatically. Note that, unlike the xml attribute, setShadowHeight(pixels) only takes the values in pixels.

StickyScrollView stickyScroll = (StickyScrollView) findViewById(R.id.sticky_scroll);
stickyScroll.setShadowDrawable(getResources().getDrawable(
        R.drawable.shadow_drawable));
stickyScroll.setShadowHeight(50); // in pixels