[AppBarLayout] Make a new setter for scroll effect and make SCROLL_EFFECT_COMPRESS public

resolves #2894

PiperOrigin-RevId: 471289613

Author: imhappi

lib/java/com/google/android/material/appbar/AppBarLayout.java

@@ -1199,14 +1199,24 @@ public static class LayoutParams extends LinearLayout.LayoutParams {
      * No effect should be placed on this view. It will scroll 1:1 with the AppBarLayout/scrolling
      * content.
      */
-    private static final int SCROLL_EFFECT_NONE = 0;
+    public static final int SCROLL_EFFECT_NONE = 0;
 
     /**
      * An effect that will "compress" this view as it hits the scroll ceiling (typically the top of
      * the screen). This is a parallax effect that masks this view and decreases its scroll ratio
      * in relation to the AppBarLayout's offset.
      */
-    private static final int SCROLL_EFFECT_COMPRESS = 1;
+    public static final int SCROLL_EFFECT_COMPRESS = 1;
+
+    /**
+     * The scroll effect to be applied when the AppBarLayout's offset changes.
+     *
+     * @hide
+     */
+    @RestrictTo(LIBRARY_GROUP)
+    @IntDef({SCROLL_EFFECT_NONE, SCROLL_EFFECT_COMPRESS})
+    @Retention(RetentionPolicy.SOURCE)
+    public @interface ScrollEffect {}
 
     private ChildScrollEffect scrollEffect;
 
@@ -1219,7 +1229,7 @@ public LayoutParams(Context c, AttributeSet attrs) {
 
       int scrollEffectInt =
           a.getInt(R.styleable.AppBarLayout_Layout_layout_scrollEffect, SCROLL_EFFECT_NONE);
-      setScrollEffect(createScrollEffectFromInt(scrollEffectInt));
+      setScrollEffect(scrollEffectInt);
 
       if (a.hasValue(R.styleable.AppBarLayout_Layout_layout_scrollInterpolator)) {
         int resId = a.getResourceId(R.styleable.AppBarLayout_Layout_layout_scrollInterpolator, 0);
@@ -1313,6 +1323,17 @@ public void setScrollEffect(@Nullable ChildScrollEffect scrollEffect) {
       this.scrollEffect = scrollEffect;
     }
 
+    /**
+     * Set the scroll effect to be applied when the AppBarLayout's offset changes.
+     *
+     * @param scrollEffect An {@code AppBarLayoutChildScrollEffect} implementation. If
+     * {@link #SCROLL_EFFECT_NONE} is passed, the scroll effect will be cleared and no
+     * effect will be applied.
+     */
+    public void setScrollEffect(@ScrollEffect int scrollEffect) {
+      this.scrollEffect = createScrollEffectFromInt(scrollEffect);
+    }
+
     /**
      * Set the interpolator to when scrolling the view associated with this {@link LayoutParams}.
      *

lib/javatests/com/google/android/material/appbar/AppBarLayoutTest.java

@@ -177,6 +177,24 @@ public void testDownNestedScrollRange_whenFirstChildNotScrollable_returnZero() {
     assertThat(appBarLayout.getDownNestedScrollRange()).isEqualTo(0);
   }
 
+  @Test
+  public void testSetScrollEffectNone_returnsNull() {
+    AppBarLayout.LayoutParams lp =
+        (AppBarLayout.LayoutParams) firstScrollableChild.getLayoutParams();
+    lp.setScrollEffect(LayoutParams.SCROLL_EFFECT_NONE);
+
+    assertThat(lp.getScrollEffect()).isEqualTo(null);
+  }
+
+  @Test
+  public void testSetScrollEffectCompress() {
+    AppBarLayout.LayoutParams lp =
+        (AppBarLayout.LayoutParams) firstScrollableChild.getLayoutParams();
+    lp.setScrollEffect(LayoutParams.SCROLL_EFFECT_COMPRESS);
+
+    assertThat(lp.getScrollEffect()).isInstanceOf(AppBarLayout.CompressChildScrollEffect.class);
+  }
+
   private static int getChildScrollRange(View child) {
     final LayoutParams lp = (LayoutParams) child.getLayoutParams();
     return getChildFullHeight(child, lp)