Add progressive disclsoure

- Add a ProgressiveDisclosureMixin that contains all logic for collapse
  preference list when it's too long
- Refactored PreferenceController's updateState to take a preference
  instead of PreferenceScreen, because with progressive disclosure the
  preference can either be in screen or the mixin. DashboardFragment is
  responsible finding the preference before passing it to controller.

Bug: 32255863
Test: RunSettingsRoboTests

Change-Id: I6713abd61c954ce12732902e5b3ca4d4c0b1563e

src/com/android/settings/dashboard/ProgressiveDisclosureMixin.java

@@ -0,0 +1,168 @@
+/*
+ * 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.dashboard;
+
+import android.content.Context;
+import android.os.Bundle;
+import android.support.v14.preference.PreferenceFragment;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceScreen;
+import android.text.TextUtils;
+import android.util.Log;
+
+import com.android.settings.core.lifecycle.LifecycleObserver;
+import com.android.settings.core.lifecycle.events.OnCreate;
+import com.android.settings.core.lifecycle.events.OnSaveInstanceState;
+import com.android.settings.overlay.FeatureFactory;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class ProgressiveDisclosureMixin implements Preference.OnPreferenceClickListener,
+        LifecycleObserver, OnCreate, OnSaveInstanceState {
+
+    private static final String TAG = "ProgressiveDisclosure";
+    private static final String STATE_USER_EXPANDED = "state_user_expanded";
+    private static final int DEFAULT_TILE_LIMIT = 3;
+
+    private int mTileLimit = DEFAULT_TILE_LIMIT;
+
+    private final DashboardFeatureProvider mDashboardFeatureProvider;
+    private final List<Preference> collapsedPrefs = new ArrayList<>();
+    private final ExpandPreference mExpandButton;
+    private final PreferenceFragment mFragment;
+
+    private boolean mUserExpanded;
+
+    public ProgressiveDisclosureMixin(Context context, PreferenceFragment fragment) {
+        mFragment = fragment;
+        mExpandButton = new ExpandPreference(context);
+        mExpandButton.setOnPreferenceClickListener(this);
+        mDashboardFeatureProvider = FeatureFactory.getFactory(context)
+                .getDashboardFeatureProvider(context);
+    }
+
+    @Override
+    public void onCreate(Bundle savedInstanceState) {
+        if (savedInstanceState != null) {
+            mUserExpanded = savedInstanceState.getBoolean(STATE_USER_EXPANDED, false);
+        }
+    }
+
+    @Override
+    public void onSaveInstanceState(Bundle outState) {
+        outState.putBoolean(STATE_USER_EXPANDED, mUserExpanded);
+    }
+
+    @Override
+    public boolean onPreferenceClick(Preference preference) {
+        if (preference instanceof ExpandPreference) {
+            final PreferenceScreen screen = mFragment.getPreferenceScreen();
+            if (screen != null) {
+                screen.removePreference(preference);
+                for (Preference pref : collapsedPrefs) {
+                    screen.addPreference(pref);
+                }
+                mUserExpanded = true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Sets the threshold to start collapsing preferences when there are too many.
+     */
+    public void setTileLimit(int limit) {
+        mTileLimit = limit;
+    }
+
+    /**
+     * Whether the controller is in collapsed state.
+     */
+    public boolean isCollapsed() {
+        return !collapsedPrefs.isEmpty();
+    }
+
+    /**
+     * Whether the screen should be collapsed.
+     */
+    public boolean shouldCollapse(PreferenceScreen screen) {
+        return mDashboardFeatureProvider.isEnabled() && screen.getPreferenceCount() >= mTileLimit
+                && !mUserExpanded;
+    }
+
+    /**
+     * Collapse extra preferences and show a "More" button
+     */
+    public void collapse(PreferenceScreen screen) {
+        final int itemCount = screen.getPreferenceCount();
+        if (!shouldCollapse(screen)) {
+            return;
+        }
+        if (!collapsedPrefs.isEmpty()) {
+            Log.w(TAG, "collapsed list should ALWAYS BE EMPTY before collapsing!");
+        }
+
+        for (int i = itemCount - 1; i >= mTileLimit; i--) {
+            final Preference preference = screen.getPreference(i);
+            addToCollapsedList(preference);
+            screen.removePreference(preference);
+        }
+        screen.addPreference(mExpandButton);
+    }
+
+    /**
+     * Add preference to collapsed list.
+     */
+    public void addToCollapsedList(Preference preference) {
+        collapsedPrefs.add(preference);
+    }
+
+    /**
+     * Remove preference from collapsed list. If the preference is not in list, do nothing.
+     */
+    public void removePreference(PreferenceScreen screen, String key) {
+        if (!isCollapsed()) {
+            return;
+        }
+        for (int i = 0; i < collapsedPrefs.size(); i++) {
+            final Preference pref = collapsedPrefs.get(i);
+            if (TextUtils.equals(key, pref.getKey())) {
+                collapsedPrefs.remove(pref);
+                if (collapsedPrefs.isEmpty()) {
+                    // Removed last element, remove expand button too.
+                    screen.removePreference(mExpandButton);
+                }
+                return;
+            }
+        }
+    }
+
+    /**
+     * Find whether a preference is in collapsed list.
+     */
+    public Preference findPreference(CharSequence key) {
+        for (int i = 0; i < collapsedPrefs.size(); i++) {
+            final Preference pref = collapsedPrefs.get(i);
+            if (TextUtils.equals(key, pref.getKey())) {
+                return pref;
+            }
+        }
+        return null;
+    }
+
+}