Build a new FooterPreference UI.

- Create a new layout for footer prefs.
- Create a new FooterPreference type to use the layout
- Create a Mixin to create and add the pref to screen
- Create a new lifecycle observer type to invoke mixin at right time
- Switch SettingsPreferenceFragment to use footer mixin.
- Switch FingerprintSettings to use the new footer pref.

Bug: 33579394
Test: RunSettingsRoboTests
Change-Id: I548ac39a0d120196a7ffed09b4f98bd9a80bae90

src/com/android/settings/widget/FooterPreference.java

@@ -0,0 +1,71 @@
+/*
+ * 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.widget;
+
+import android.content.Context;
+import android.support.v7.preference.Preference;
+import android.support.v7.preference.PreferenceViewHolder;
+import android.text.method.LinkMovementMethod;
+import android.util.AttributeSet;
+import android.widget.TextView;
+
+import com.android.settings.R;
+
+/**
+ * A custom preference acting as "footer" of a page. It has a field for icon and text. It is added
+ * to screen as the last preference.
+ */
+public class FooterPreference extends Preference {
+
+    static final int ORDER_FOOTER = Integer.MAX_VALUE - 1;
+    static final String KEY_FOOTER = "footer_preference";
+
+    public FooterPreference(Context context, AttributeSet attrs,
+            int defStyleAttr, int defStyleRes) {
+        super(context, attrs, defStyleAttr, defStyleRes);
+        init();
+    }
+
+    public FooterPreference(Context context, AttributeSet attrs, int defStyleAttr) {
+        super(context, attrs, defStyleAttr);
+        init();
+    }
+
+    public FooterPreference(Context context, AttributeSet attrs) {
+        super(context, attrs);
+        init();
+    }
+
+    public FooterPreference(Context context) {
+        super(context);
+        init();
+    }
+
+    @Override
+    public void onBindViewHolder(PreferenceViewHolder holder) {
+        super.onBindViewHolder(holder);
+        TextView title = (TextView) holder.itemView.findViewById(android.R.id.title);
+        title.setMovementMethod(new LinkMovementMethod());
+    }
+
+    private void init() {
+        setLayoutResource(R.layout.preference_footer);
+        setIcon(R.drawable.ic_info_outline_24dp);
+        setKey(KEY_FOOTER);
+        setOrder(ORDER_FOOTER);
+    }
+}

src/com/android/settings/widget/FooterPreferenceMixin.java

@@ -0,0 +1,71 @@
+/*
+ * 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.widget;
+
+import android.content.Context;
+import android.support.v14.preference.PreferenceFragment;
+import android.support.v7.preference.PreferenceScreen;
+
+import com.android.settings.core.lifecycle.Lifecycle;
+import com.android.settings.core.lifecycle.LifecycleObserver;
+import com.android.settings.core.lifecycle.events.SetPreferenceScreen;
+
+public class FooterPreferenceMixin implements LifecycleObserver, SetPreferenceScreen {
+
+    private final PreferenceFragment mFragment;
+    private FooterPreference mFooterPreference;
+
+    public FooterPreferenceMixin(PreferenceFragment fragment, Lifecycle lifecycle) {
+        mFragment = fragment;
+        lifecycle.addObserver(this);
+    }
+
+    @Override
+    public void setPreferenceScreen(PreferenceScreen preferenceScreen) {
+        if (mFooterPreference != null) {
+            preferenceScreen.addPreference(mFooterPreference);
+        }
+    }
+
+    /**
+     * Creates a new {@link FooterPreference}.
+     */
+    public FooterPreference createFooterPreference() {
+        final PreferenceScreen screen = mFragment.getPreferenceScreen();
+        if (mFooterPreference != null && screen != null) {
+            screen.removePreference(mFooterPreference);
+        }
+        mFooterPreference = new FooterPreference(getPrefContext());
+
+        if (screen != null) {
+            screen.addPreference(mFooterPreference);
+        }
+        return mFooterPreference;
+    }
+
+    /**
+     * Returns an UI context with theme properly set for new Preference objects.
+     */
+    private Context getPrefContext() {
+        return mFragment.getPreferenceManager().getContext();
+    }
+
+    public boolean hasFooter() {
+        return mFooterPreference != null;
+    }
+}
+