Make RecyclerView smooth scroll speed customizable

app/src/main/java/com/hippo/ehviewer/widget/ContentLayout.java

@@ -350,7 +350,9 @@ public class ContentLayout extends FrameLayout {
                         if (mCurrentTaskType == TYPE_PRE_PAGE_KEEP_POS) {
                             mFirstIndex += pageVolume;
                             mLastIndex += pageVolume;
-                            // TODO
+
+                            mRecyclerView.stopScroll();
+                            LayoutManagerUtils.smoothScrollToPosition(mLayoutManager, mContext, mFirstIndex - 1, 100);
                         } else {
                             mCurrentPage = mFirstPage;
                             mFirstIndex = 0;
@@ -464,7 +466,8 @@ public class ContentLayout extends FrameLayout {
             if (mViewTransition.getShownViewIndex() == 0) {
                 // Go to top
                 mRecyclerView.stopScroll();
-                mLayoutManager.smoothScrollToPosition(mRecyclerView, null, 0);
+                LayoutManagerUtils.scrollToPositionWithOffset(mLayoutManager, 0, 0);
+                onScrollToPosition();
                 // Show header refresh
                 mRefreshLayout.setFooterRefreshing(false);
                 mRefreshLayout.setHeaderRefreshing(true);

app/src/main/java/com/hippo/util/LayoutManagerUtils.java

@@ -15,10 +15,14 @@
 
 package com.hippo.util;
 
+import android.content.Context;
+import android.graphics.PointF;
 import android.support.v7.widget.LinearLayoutManager;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.StaggeredGridLayoutManager;
 
+import com.hippo.widget.recyclerview.SimpleSmoothScroller;
+
 public final class LayoutManagerUtils {
 
     public static void scrollToPositionWithOffset(
@@ -33,6 +37,47 @@ public final class LayoutManagerUtils {
         }
     }
 
+    public static void smoothScrollToPosition(
+            RecyclerView.LayoutManager layoutManager, Context context, int position) {
+        smoothScrollToPosition(layoutManager, context, position, -1);
+    }
+
+    public static void smoothScrollToPosition(
+            RecyclerView.LayoutManager layoutManager, Context context, int position,
+            int millisecondsPerInch) {
+        SimpleSmoothScroller smoothScroller;
+        if (layoutManager instanceof LinearLayoutManager) {
+            final LinearLayoutManager linearLayoutManager = (LinearLayoutManager) layoutManager;
+            smoothScroller = new SimpleSmoothScroller(context, millisecondsPerInch) {
+                @Override
+                public PointF computeScrollVectorForPosition(int targetPosition) {
+                    return linearLayoutManager.computeScrollVectorForPosition(targetPosition);
+                }
+            };
+        } else if (layoutManager instanceof StaggeredGridLayoutManager) {
+            final StaggeredGridLayoutManager staggeredGridLayoutManager = (StaggeredGridLayoutManager) layoutManager;
+            smoothScroller = new SimpleSmoothScroller(context, millisecondsPerInch) {
+                @Override
+                public PointF computeScrollVectorForPosition(int targetPosition) {
+                    final int direction = staggeredGridLayoutManager.calculateScrollDirectionForPosition(targetPosition);
+                    if (direction == 0) {
+                        return null;
+                    }
+                    if (staggeredGridLayoutManager.getOrientation() == StaggeredGridLayoutManager.HORIZONTAL) {
+                        return new PointF(direction, 0);
+                    } else {
+                        return new PointF(0, direction);
+                    }
+                }
+            };
+        } else {
+            throw new IllegalStateException("Can't do smoothScrollToPosition for " +
+                    layoutManager.getClass().getName());
+        }
+        smoothScroller.setTargetPosition(position);
+        layoutManager.startSmoothScroll(smoothScroller);
+    }
+
     public static int getFirstVisibleItemPostion(RecyclerView.LayoutManager layoutManager) {
         if (layoutManager instanceof LinearLayoutManager) {
             return ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();

app/src/main/java/com/hippo/widget/recyclerview/SimpleSmoothScroller.java

@@ -0,0 +1,38 @@
+/*
+ * Copyright (C) 2015 Hippo Seven
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.hippo.widget.recyclerview;
+
+import android.content.Context;
+import android.support.v7.widget.LinearSmoothScroller;
+
+public abstract class SimpleSmoothScroller extends LinearSmoothScroller {
+
+    private float mMillisecondsPerPx;
+
+    public SimpleSmoothScroller(Context context, float millisecondsPerInch) {
+        super(context);
+        mMillisecondsPerPx = millisecondsPerInch / context.getResources().getDisplayMetrics().densityDpi;
+    }
+
+    @Override
+    protected int calculateTimeForScrolling(int dx) {
+        if (mMillisecondsPerPx <= 0) {
+            return super.calculateTimeForScrolling(dx);
+        } else {
+            return (int) Math.ceil(Math.abs(dx) * mMillisecondsPerPx);
+        }
+    }
+}