Add RecyclerView helper

app/src/main/java/android/support/v7/widget/helper/ItemTouchUIUtil.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * 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
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * 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 android.support.v7.widget.helper;
+
+import android.graphics.Canvas;
+import android.support.v7.widget.RecyclerView;
+import android.view.View;
+
+/**
+ * Utility class for {@link ItemTouchHelper} which handles item transformations for different
+ * API versions.
+ * <p/>
+ * This class has methods that map to {@link ItemTouchHelper.Callback}'s drawing methods. Default
+ * implementations in {@link ItemTouchHelper.Callback} call these methods with
+ * {@link RecyclerView.ViewHolder#itemView} and {@link ItemTouchUIUtil} makes necessary changes
+ * on the View depending on the API level. You can access the instance of {@link ItemTouchUIUtil}
+ * via {@link ItemTouchHelper.Callback#getDefaultUIUtil()} and call its methods with the children
+ * of ViewHolder that you want to apply default effects.
+ *
+ * @see ItemTouchHelper.Callback#getDefaultUIUtil()
+ */
+public interface ItemTouchUIUtil {
+
+    /**
+     * The default implementation for {@link ItemTouchHelper.Callback#onChildDraw(Canvas,
+     * RecyclerView, RecyclerView.ViewHolder, float, float, int, boolean)}
+     */
+    void onDraw(Canvas c, RecyclerView recyclerView, View view,
+            float dX, float dY, int actionState, boolean isCurrentlyActive);
+
+    /**
+     * The default implementation for {@link ItemTouchHelper.Callback#onChildDrawOver(Canvas,
+     * RecyclerView, RecyclerView.ViewHolder, float, float, int, boolean)}
+     */
+    void onDrawOver(Canvas c, RecyclerView recyclerView, View view,
+            float dX, float dY, int actionState, boolean isCurrentlyActive);
+
+    /**
+     * The default implementation for {@link ItemTouchHelper.Callback#clearView(RecyclerView,
+     * RecyclerView.ViewHolder)}
+     */
+    void clearView(View view);
+
+    /**
+     * The default implementation for {@link ItemTouchHelper.Callback#onSelectedChanged(
+     * RecyclerView.ViewHolder, int)}
+     */
+    void onSelected(View view);
+}
+

app/src/main/java/android/support/v7/widget/helper/ItemTouchUIUtilImpl.java

@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2015 The Android Open Source Project
+ *
+ * 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
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * 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 android.support.v7.widget.helper;
+
+import android.graphics.Canvas;
+import android.support.v4.view.ViewCompat;
+import android.support.v7.widget.RecyclerView;
+import android.view.View;
+
+import com.hippo.ehviewer.R;
+
+/**
+ * Package private class to keep implementations. Putting them inside ItemTouchUIUtil makes them
+ * public API, which is not desired in this case.
+ */
+class ItemTouchUIUtilImpl {
+    static class Lollipop extends Honeycomb {
+        @Override
+        public void onDraw(Canvas c, RecyclerView recyclerView, View view,
+                float dX, float dY, int actionState, boolean isCurrentlyActive) {
+            if (isCurrentlyActive) {
+                Object originalElevation = view.getTag(R.id.item_touch_helper_previous_elevation);
+                if (originalElevation == null) {
+                    originalElevation = ViewCompat.getElevation(view);
+                    float newElevation = 1f + findMaxElevation(recyclerView, view);
+                    ViewCompat.setElevation(view, newElevation);
+                    view.setTag(R.id.item_touch_helper_previous_elevation, originalElevation);
+                }
+            }
+            super.onDraw(c, recyclerView, view, dX, dY, actionState, isCurrentlyActive);
+        }
+
+        private float findMaxElevation(RecyclerView recyclerView, View itemView) {
+            final int childCount = recyclerView.getChildCount();
+            float max = 0;
+            for (int i = 0; i < childCount; i++) {
+                final View child = recyclerView.getChildAt(i);
+                if (child == itemView) {
+                    continue;
+                }
+                final float elevation = ViewCompat.getElevation(child);
+                if (elevation > max) {
+                    max = elevation;
+                }
+            }
+            return max;
+        }
+
+        @Override
+        public void clearView(View view) {
+            final Object tag = view.getTag(R.id.item_touch_helper_previous_elevation);
+            if (tag != null && tag instanceof Float) {
+                ViewCompat.setElevation(view, (Float) tag);
+            }
+            view.setTag(R.id.item_touch_helper_previous_elevation, null);
+            super.clearView(view);
+        }
+    }
+
+    static class Honeycomb implements ItemTouchUIUtil {
+
+        @Override
+        public void clearView(View view) {
+            ViewCompat.setTranslationX(view, 0f);
+            ViewCompat.setTranslationY(view, 0f);
+        }
+
+        @Override
+        public void onSelected(View view) {
+
+        }
+
+        @Override
+        public void onDraw(Canvas c, RecyclerView recyclerView, View view,
+                float dX, float dY, int actionState, boolean isCurrentlyActive) {
+            ViewCompat.setTranslationX(view, dX);
+            ViewCompat.setTranslationY(view, dY);
+        }
+
+        @Override
+        public void onDrawOver(Canvas c, RecyclerView recyclerView,
+                View view, float dX, float dY, int actionState, boolean isCurrentlyActive) {
+
+        }
+    }
+
+    static class Gingerbread implements ItemTouchUIUtil {
+
+        private void draw(Canvas c, RecyclerView parent, View view,
+                float dX, float dY) {
+            c.save();
+            c.translate(dX, dY);
+            parent.drawChild(c, view, 0);
+            c.restore();
+        }
+
+        @Override
+        public void clearView(View view) {
+            view.setVisibility(View.VISIBLE);
+        }
+
+        @Override
+        public void onSelected(View view) {
+            view.setVisibility(View.INVISIBLE);
+        }
+
+        @Override
+        public void onDraw(Canvas c, RecyclerView recyclerView, View view,
+                float dX, float dY, int actionState, boolean isCurrentlyActive) {
+            if (actionState != ItemTouchHelper.ACTION_STATE_DRAG) {
+                draw(c, recyclerView, view, dX, dY);
+            }
+        }
+
+        @Override
+        public void onDrawOver(Canvas c, RecyclerView recyclerView,
+                View view, float dX, float dY,
+                int actionState, boolean isCurrentlyActive) {
+            if (actionState == ItemTouchHelper.ACTION_STATE_DRAG) {
+                draw(c, recyclerView, view, dX, dY);
+            }
+        }
+    }
+}