Accomodating multiple preview screen with ViewPager for the users to

swipe across, along with some UI refinements.

Change-Id: I9487bcce88cdab490a4b6baa752224acddc5be52

src/com/android/settings/PreviewPagerAdapter.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright (C) 2016 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 com.android.settings;
+
+import android.content.Context;
+import android.content.res.Configuration;
+import android.support.v4.view.PagerAdapter;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.animation.AccelerateInterpolator;
+import android.view.animation.DecelerateInterpolator;
+import android.view.animation.Interpolator;
+import android.widget.FrameLayout;
+
+/**
+ * A PagerAdapter used by PreviewSeekBarPreferenceFragment that for showing multiple preview screen
+ * regarding a single setting and allowing the user to swipe across them.
+ */
+public class PreviewPagerAdapter extends PagerAdapter {
+
+    private TouchBlockingFrameLayout[] mPreviewFrames;
+
+    /** Duration to use when cross-fading between previews. */
+    private static final long CROSS_FADE_DURATION_MS = 400;
+
+    /** Interpolator to use when cross-fading between previews. */
+    private static final Interpolator FADE_IN_INTERPOLATOR = new DecelerateInterpolator();
+
+    /** Interpolator to use when cross-fading between previews. */
+    private static final Interpolator FADE_OUT_INTERPOLATOR = new AccelerateInterpolator();
+
+    public PreviewPagerAdapter(Context context, int[] previewSampleResIds,
+                               Configuration[] configurations) {
+        mPreviewFrames = new TouchBlockingFrameLayout[previewSampleResIds.length];
+
+        for (int i = 0; i < previewSampleResIds.length; ++i) {
+            mPreviewFrames[i] = (TouchBlockingFrameLayout) LayoutInflater.from(context)
+                    .inflate(R.layout.preview_frame_container, null);
+
+            for (Configuration configuration : configurations) {
+                // Create a new configuration for the specified value. It won't
+                // have any theme set, so manually apply the current theme.
+                final Context configContext = context.createConfigurationContext(configuration);
+                configContext.setTheme(context.getThemeResId());
+
+                final LayoutInflater configInflater = LayoutInflater.from(configContext);
+                final View sampleView = configInflater.inflate(previewSampleResIds[i],
+                        mPreviewFrames[i], false);
+                sampleView.setAlpha(0);
+                sampleView.setVisibility(View.INVISIBLE);
+
+                mPreviewFrames[i].addView(sampleView);
+            }
+        }
+    }
+
+    @Override
+    public void destroyItem (ViewGroup container, int position, Object object) {
+        container.removeView((View) object);
+    }
+
+    @Override
+    public int getCount() {
+        return mPreviewFrames.length;
+    }
+
+    @Override
+    public Object instantiateItem(ViewGroup container, int position) {
+        container.addView(mPreviewFrames[position]);
+        return mPreviewFrames[position];
+    }
+
+    @Override
+    public boolean isViewFromObject(View view, Object object) {
+        return (view == object);
+    }
+
+    void setPreviewLayer(int newIndex, int currentIndex, int currentItem, boolean animate) {
+        for (FrameLayout previewFrame : mPreviewFrames) {
+            if (currentIndex >= 0) {
+                final View lastLayer = previewFrame.getChildAt(currentIndex);
+                if (animate && previewFrame == mPreviewFrames[currentItem]) {
+                    lastLayer.animate()
+                            .alpha(0)
+                            .setInterpolator(FADE_OUT_INTERPOLATOR)
+                            .setDuration(CROSS_FADE_DURATION_MS)
+                            .withEndAction(new Runnable() {
+                                @Override
+                                public void run() {
+                                    lastLayer.setVisibility(View.INVISIBLE);
+                                }
+                            });
+                } else {
+                    lastLayer.setAlpha(0);
+                    lastLayer.setVisibility(View.INVISIBLE);
+                }
+            }
+
+            final View nextLayer = previewFrame.getChildAt(newIndex);
+            if (animate && previewFrame == mPreviewFrames[currentItem]) {
+                nextLayer.animate()
+                        .alpha(1)
+                        .setInterpolator(FADE_IN_INTERPOLATOR)
+                        .setDuration(CROSS_FADE_DURATION_MS)
+                        .withStartAction(new Runnable() {
+                            @Override
+                            public void run() {
+                                nextLayer.setVisibility(View.VISIBLE);
+                            }
+                        });
+            } else {
+                nextLayer.setVisibility(View.VISIBLE);
+                nextLayer.setAlpha(1);
+            }
+        }
+    }
+}