Lemberg Lemberg - 26 days ago 11
Android Question

Change view transparrency in CoordinatorLayout

I have the following screen

main screen

What I want to achieve is when I scroll up the view, and the

AppBarLayout
is collapsed the "TEST TEXT" becomes transparrent. What is the best way to do this? May I achieve this with xml only or do I need to write code.

enter image description here

Here is my xml

<android.support.design.widget.CoordinatorLayout
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/background_light"
android:fitsSystemWindows="true">

<android.support.design.widget.AppBarLayout
android:id="@+id/main.appbar"
android:layout_width="match_parent"
android:layout_height="300dp"
android:background="@android:color/transparent"
android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
android:fitsSystemWindows="true">

<android.support.design.widget.CollapsingToolbarLayout
android:id="@+id/main.collapsing"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_scrollFlags="scroll|exitUntilCollapsed"
android:fitsSystemWindows="true"
app:contentScrim="@android:color/transparent"
app:expandedTitleMarginStart="48dp"
app:expandedTitleMarginEnd="64dp">

<ImageView
android:id="@+id/main.backdrop"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="centerCrop"
android:fitsSystemWindows="true"
android:src="@drawable/material_flat"
app:layout_collapseMode="parallax"/>

<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:scaleType="centerCrop"
android:gravity="center"
android:textSize="26sp"
android:text="TEST TEXT"
app:layout_collapseMode="parallax"/>

<android.support.v7.widget.Toolbar
android:id="@+id/main.toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
app:popupTheme="@style/ThemeOverlay.AppCompat.Light"
app:layout_collapseMode="pin"
/>
</android.support.design.widget.CollapsingToolbarLayout>
</android.support.design.widget.AppBarLayout>

<android.support.v4.widget.NestedScrollView
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
>

<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textSize="20sp"
android:lineSpacingExtra="8dp"
android:text="@string/lorem"
android:padding="@dimen/activity_horizontal_margin"
/>
</android.support.v4.widget.NestedScrollView>

<android.support.design.widget.FloatingActionButton
android:layout_height="wrap_content"
android:layout_width="wrap_content"
android:layout_margin="@dimen/activity_horizontal_margin"
android:src="@drawable/ic_comment_24dp"
app:layout_anchor="@id/main.appbar"
app:layout_anchorGravity="bottom|right|end"
/>



Answer
mAppBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener() {
    @Override
    public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
        if (verticalOffset == -mCollapsingToolbarLayout.getHeight() + mToolbar.getHeight()) {

           //change color of textview.
           textview.setBackgroundColor(Color.TRANSPARENT);
        }
    }
});