Centering cells working

Author: Iain Connor

library/src/main/java/com/tippingcanoe/dewey/Dewey.java

@@ -10,6 +10,7 @@
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.util.AttributeSet;
+import android.util.Log;
 import android.view.animation.AccelerateDecelerateInterpolator;
 import android.view.animation.AccelerateInterpolator;
 import android.view.animation.Interpolator;
@@ -77,7 +78,23 @@ protected void setup ( Context context, @Nullable AttributeSet attrs ) {
 		setHasFixedSize(true);
 		setHorizontalScrollBarEnabled(false);
 
-		setFocusedPosition(0, false);
+		setFocusedPosition(0, false, true);
+	}
+
+	protected int adjustPositionToCenterIfNeeded(int inputPosition) {
+		if ( inputPosition != focusedPosition && layoutManager != null && layoutManager.areCellsUniform() && layoutManager.getUniformCellWidth() != 0 ) {
+			boolean scrollingRight = inputPosition > focusedPosition;
+			float cellsInView = ((float) getMeasuredWidth() / (float) layoutManager.getUniformCellWidth());
+			int cellsToCenter = (int) Math.floor((cellsInView / 2.0f));
+			int offset = (scrollingRight ? 1 : -1) * cellsToCenter;
+			int adjustedPosition = Math.min(inputPosition + offset, getAdapter().getItemCount() - 1);
+
+			if ( adjustedPosition >= 0 && inputPosition >= offset ) {
+				return adjustedPosition;
+			}
+		}
+
+		return inputPosition;
 	}
 
 	public void setFocusedPosition ( int position, boolean animated ) {
@@ -89,20 +106,23 @@ public void setFocusedPosition ( int position, boolean animated, boolean silentl
 			onFocusedPositionChangedListener.onFocusedPositionChanged(focusedPosition, position);
 		}
 
-		boolean requestedPositionIsVisible = position >= getChildAdapterPosition(getChildAt(0)) && position <= getChildAdapterPosition(getChildAt(getChildCount() - 1));
+		int adjustedScrollTarget = adjustPositionToCenterIfNeeded(position);
 
-		// @TODO, enhance this by attempting to center the focused position.
-		if (requestedPositionIsVisible && animated) {
+		if (requestedPositionIsVisible(position) && requestedPositionIsVisible(adjustedScrollTarget) && animated) {
 			deweyDecorator.startAnimation(focusedPosition, position);
 		} else if (animated) {
-			smoothScrollToPosition(position);
+			smoothScrollToPosition(adjustedScrollTarget);
 		} else {
-			scrollToPosition(position);
+			scrollToPosition(adjustedScrollTarget);
 		}
 
 		focusedPosition = position;
 	}
 
+	public boolean requestedPositionIsVisible ( int position ) {
+		return position >= getChildAdapterPosition(getChildAt(0)) && position <= getChildAdapterPosition(getChildAt(getChildCount() - 1));
+	}
+
 	@Override
 	public void setAdapter ( Adapter adapter ) {
 		super.setAdapter(adapter);

library/src/main/java/com/tippingcanoe/dewey/DeweyDecorator.java

@@ -324,7 +324,7 @@ public void startAnimation ( int previouslyFocusedPosition, int newFocusedPositi
 			int maxVisiblePos = 0;
 
 			for (int i = 0; i < dewey.getChildCount(); i++) {
-				int childPosition = dewey.getChildPosition(dewey.getChildAt(i));
+				int childPosition = dewey.getChildLayoutPosition(dewey.getChildAt(i));
 
 				if (childPosition != RecyclerView.NO_POSITION) {
 					if (childPosition == previouslyFocusedPosition) {

library/src/main/java/com/tippingcanoe/dewey/DeweyLayoutManager.java

@@ -128,6 +128,10 @@ public boolean areCellsUniform() {
 		return uniformCells;
 	}
 
+	public int getUniformCellWidth() {
+		return uniformCellWidth;
+	}
+
 	public void setUniformCells(boolean uniformCells) {
 		this.uniformCells = uniformCells;
 	}