Managing Edge Glow Color in Nested ScrollView in Open Event Android App

After the introduction of material design by Google many new UI elements have been introduced. Material design is based on the interaction and movement of colours and objects in real world rather than synthetic unnatural phenomenon. Sometimes it gets messy when we try to keep up with our material aesthetic. The most popular example of it is edge glow colour. The edge glow colour of ListView, RecyclerView, ScrollView and NestedScrollView is managed by the accent colour declared in the styles. We cannot change the accent colour of a particular activity as it is a constant, so it is same across entire app but in popular apps like Contacts by Google it appears different for every individual contacts. Fixing an issue in Open Event Android app, I came across the same problem. In this tutorial I solve this problem particularly for NestedScrollView. See the bottom of screenshots for comparison.

   
  • You need to pre check if the Android version is above or equal to LOLLIPOP before doing this as the setColor() function for edge glow is introduced in LOLLIPOP
  • The fields are declared as “mEdgeGlowTop” and “mEdgeGlowBottom” that we have to modify.
  • We get the glow property of NestedScrollView through EdgeEffectCompat class instead of EdgeEffect class directly, unlike for ListView due its new introduction.

Let’s have a look at the function which accepts arguments color as an integer and nested scroll view of which the color has to be set.

First you have to get the fields “mEdgeGlowTop” and “mEdgeGlowBottom” that signifies the bubbles that are generated when you scroll up and down from Nested Scroll View Class. Similarly “mEdgeGlowLeft”  and “mEdgeGlowRight” for the horizontal scrolling.

public static void changeGlowColor(int color, NestedScrollView scrollView) {
   try {

       Field edgeGlowTop = NestedScrollView.class.getDeclaredField("mEdgeGlowTop");

       edgeGlowTop.setAccessible(true);

       Field edgeGlowBottom = NestedScrollView.class.getDeclaredField("mEdgeGlowBottom");

       edgeGlowBottom.setAccessible(true);

Get the reference to edge effect which is the different part unlike recycler view or list view of setting the edge glow color in nested scrollview.

EdgeEffectCompat edgeEffect = (EdgeEffectCompat) edgeGlowTop.get(scrollView);

       if (edgeEffect == null) {
           edgeEffect = new EdgeEffectCompat(scrollView.getContext());
           edgeGlowTop.set(scrollView, edgeEffect);
       }

       Views.setEdgeGlowColor(edgeEffect, color);

       edgeEffect = (EdgeEffectCompat) edgeGlowBottom.get(scrollView);
       if (edgeEffect == null) {
           edgeEffect = new EdgeEffectCompat(scrollView.getContext());
           edgeGlowBottom.set(scrollView, edgeEffect);
       }

       Views.setEdgeGlowColor(edgeEffect, color);

   } catch (Exception ex) {

       ex.printStackTrace();
   }

}

Finally set the edge glow color. This only works for the versions that are above or equal to LOLLIPOP as edge effect was introduced in the android beginning from those versions.

@TargetApi(Build.VERSION_CODES.LOLLIPOP)

public static void setEdgeGlowColor(@NonNull EdgeEffectCompat edgeEffect, @ColorInt int color) throws Exception {
        Field field = EdgeEffectCompat.class.getDeclaredField("mEdgeEffect");

        field.setAccessible(true);
        EdgeEffect effect = (EdgeEffect) field.get(edgeEffect);
        
        if (effect != null)
            effect.setColor(color);
    }

 

(Don’t forget to catch any exception. You can monitor them by using Log.e(“Error”, ”Message”, e ); for debugging and testing).

Resources

  • https://developer.android.com/reference/android/support/v4/widget/NestedScrollView.html