diff --git a/core/java/android/provider/Settings.java b/core/java/android/provider/Settings.java
index 58595c2..de677f6 100755
--- a/core/java/android/provider/Settings.java
+++ b/core/java/android/provider/Settings.java
@@ -5511,6 +5511,16 @@
                 "accessibility_shortcut_target_service";
 
         /**
+         * Setting specifying the accessibility service or feature to be toggled via the
+         * accessibility button in the navigation bar. This is either a flattened
+         * {@link ComponentName} or the class name of a system class implementing a supported
+         * accessibility feature.
+         * @hide
+         */
+        public static final String ACCESSIBILITY_BUTTON_TARGET_COMPONENT =
+                "accessibility_button_target_component";
+
+        /**
          * If touch exploration is enabled.
          */
         public static final String TOUCH_EXPLORATION_ENABLED = "touch_exploration_enabled";
@@ -6997,6 +7007,7 @@
             TOUCH_EXPLORATION_ENABLED,
             ACCESSIBILITY_ENABLED,
             ACCESSIBILITY_SHORTCUT_TARGET_SERVICE,
+            ACCESSIBILITY_BUTTON_TARGET_COMPONENT,
             ACCESSIBILITY_SHORTCUT_DIALOG_SHOWN,
             ACCESSIBILITY_SHORTCUT_ENABLED,
             ACCESSIBILITY_SHORTCUT_ON_LOCK_SCREEN,
diff --git a/core/java/android/view/accessibility/AccessibilityManager.java b/core/java/android/view/accessibility/AccessibilityManager.java
index c9f9f31..35276cc 100644
--- a/core/java/android/view/accessibility/AccessibilityManager.java
+++ b/core/java/android/view/accessibility/AccessibilityManager.java
@@ -22,6 +22,7 @@
 import android.accessibilityservice.AccessibilityServiceInfo;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
+import android.annotation.SdkConstant;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.pm.PackageManager;
@@ -97,6 +98,22 @@
     /** @hide */
     public static final int AUTOCLICK_DELAY_DEFAULT = 600;
 
+    /**
+     * Activity action: Launch UI to manage which accessibility service or feature is assigned
+     * to the navigation bar Accessibility button.
+     * <p>
+     * Input: Nothing.
+     * </p>
+     * <p>
+     * Output: Nothing.
+     * </p>
+     *
+     * @hide
+     */
+    @SdkConstant(SdkConstant.SdkConstantType.ACTIVITY_INTENT_ACTION)
+    public static final String ACTION_CHOOSE_ACCESSIBILITY_BUTTON =
+            "android.intent.action.CHOOSE_ACCESSIBILITY_BUTTON";
+
     static final Object sInstanceSync = new Object();
 
     private static AccessibilityManager sInstance;
diff --git a/core/java/com/android/internal/app/AccessibilityButtonChooserActivity.java b/core/java/com/android/internal/app/AccessibilityButtonChooserActivity.java
new file mode 100644
index 0000000..ee5d339
--- /dev/null
+++ b/core/java/com/android/internal/app/AccessibilityButtonChooserActivity.java
@@ -0,0 +1,174 @@
+/*
+ * Copyright (C) 2017 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.internal.app;
+
+import android.accessibilityservice.AccessibilityServiceInfo;
+import android.annotation.NonNull;
+import android.annotation.Nullable;
+import android.app.Activity;
+import android.content.Context;
+import android.graphics.drawable.Drawable;
+import android.os.Bundle;
+import android.provider.Settings;
+import android.text.TextUtils;
+import android.view.LayoutInflater;
+import android.view.View;
+import android.view.ViewGroup;
+import android.view.accessibility.AccessibilityManager;
+import android.widget.BaseAdapter;
+import android.widget.GridView;
+import android.widget.ImageView;
+import android.widget.TextView;
+
+import com.android.internal.R;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Activity used to display and persist a service or feature target for the Accessibility button.
+ */
+public class AccessibilityButtonChooserActivity extends Activity {
+
+    private static final String MAGNIFICATION_COMPONENT_ID =
+            "com.android.server.accessibility.MagnificationController";
+
+    private AccessibilityButtonTarget mMagnificationTarget = null;
+
+    private List<AccessibilityButtonTarget> mTargets = null;
+
+    @Override
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+        setContentView(R.layout.accessibility_button_chooser);
+
+        String component = Settings.Secure.getString(getContentResolver(),
+                Settings.Secure.ACCESSIBILITY_BUTTON_TARGET_COMPONENT);
+        if (TextUtils.isEmpty(component)) {
+            TextView prompt = (TextView) findViewById(R.id.accessibility_button_prompt);
+            prompt.setVisibility(View.VISIBLE);
+        }
+
+        mMagnificationTarget = new AccessibilityButtonTarget(this, MAGNIFICATION_COMPONENT_ID,
+                R.string.accessibility_magnification_chooser_text,
+                R.drawable.resolver_icon_placeholder);
+
+        mTargets = getServiceAccessibilityButtonTargets(this);
+        if (Settings.Secure.getInt(getContentResolver(),
+                Settings.Secure.ACCESSIBILITY_DISPLAY_MAGNIFICATION_NAVBAR_ENABLED, 0) == 1) {
+            mTargets.add(mMagnificationTarget);
+        }
+
+        if (mTargets.size() < 2) {
+            // Why are we here?
+            finish();
+        }
+
+        GridView gridview = (GridView) findViewById(R.id.accessibility_button_chooser_grid);
+        gridview.setAdapter(new TargetAdapter());
+        gridview.setOnItemClickListener((parent, view, position, id) -> {
+            onTargetSelected(mTargets.get(position));
+        });
+    }
+
+    private static List<AccessibilityButtonTarget> getServiceAccessibilityButtonTargets(
+            @NonNull Context context) {
+        AccessibilityManager ams = (AccessibilityManager) context.getSystemService(
+                Context.ACCESSIBILITY_SERVICE);
+        List<AccessibilityServiceInfo> services = ams.getEnabledAccessibilityServiceList(
+                AccessibilityServiceInfo.FEEDBACK_ALL_MASK);
+        if (services == null) {
+            return Collections.emptyList();
+        }
+
+        ArrayList<AccessibilityButtonTarget> targets = new ArrayList<>(services.size());
+        for (AccessibilityServiceInfo info : services) {
+            if ((info.flags & AccessibilityServiceInfo.FLAG_REQUEST_ACCESSIBILITY_BUTTON) != 0) {
+                targets.add(new AccessibilityButtonTarget(context, info));
+            }
+        }
+
+        return targets;
+    }
+
+    private void onTargetSelected(AccessibilityButtonTarget target) {
+        Settings.Secure.putString(getContentResolver(),
+                Settings.Secure.ACCESSIBILITY_BUTTON_TARGET_COMPONENT, target.getId());
+        finish();
+    }
+
+    private class TargetAdapter extends BaseAdapter {
+        @Override
+        public int getCount() {
+            return mTargets.size();
+        }
+
+        @Override
+        public Object getItem(int position) {
+            return null;
+        }
+
+        @Override
+        public long getItemId(int position) {
+            return position;
+        }
+
+        @Override
+        public View getView(int position, View convertView, ViewGroup parent) {
+            LayoutInflater inflater = AccessibilityButtonChooserActivity.this.getLayoutInflater();
+            View root = inflater.inflate(R.layout.accessibility_button_chooser_item, parent, false);
+            final AccessibilityButtonTarget target = mTargets.get(position);
+            ImageView iconView = root.findViewById(R.id.accessibility_button_target_icon);
+            TextView labelView = root.findViewById(R.id.accessibility_button_target_label);
+            iconView.setImageDrawable(target.getDrawable());
+            labelView.setText(target.getLabel());
+            return root;
+        }
+    }
+
+    private static class AccessibilityButtonTarget {
+        public String mId;
+        public CharSequence mLabel;
+        public Drawable mDrawable;
+
+        public AccessibilityButtonTarget(@NonNull Context context,
+                @NonNull AccessibilityServiceInfo serviceInfo) {
+            this.mId = serviceInfo.getComponentName().flattenToString();
+            this.mLabel = serviceInfo.getResolveInfo().loadLabel(context.getPackageManager());
+            this.mDrawable = serviceInfo.getResolveInfo().loadIcon(context.getPackageManager());
+        }
+
+        public AccessibilityButtonTarget(Context context, @NonNull String id, int labelResId,
+                int iconRes) {
+            this.mId = id;
+            this.mLabel = context.getText(labelResId);
+            this.mDrawable = context.getDrawable(iconRes);
+        }
+
+        public String getId() {
+            return mId;
+        }
+
+        public CharSequence getLabel() {
+            return mLabel;
+        }
+
+        public Drawable getDrawable() {
+            return mDrawable;
+        }
+    }
+}
\ No newline at end of file
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 8abd022..8721f34 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -3344,6 +3344,19 @@
                 <category android:name="android.intent.category.VOICE" />
             </intent-filter>
         </activity>
+        <activity android:name="com.android.internal.app.AccessibilityButtonChooserActivity"
+                  android:theme="@style/Theme.DeviceDefault.Resolver"
+                  android:finishOnCloseSystemDialogs="true"
+                  android:excludeFromRecents="true"
+                  android:documentLaunchMode="never"
+                  android:relinquishTaskIdentity="true"
+                  android:configChanges="screenSize|smallestScreenSize|screenLayout|orientation|keyboard|keyboardHidden"
+                  android:process=":ui">
+            <intent-filter>
+                <action android:name="android.intent.action.CHOOSE_ACCESSIBILITY_BUTTON" />
+                <category android:name="android.intent.category.DEFAULT" />
+            </intent-filter>
+        </activity>
         <activity android:name="com.android.internal.app.IntentForwarderActivity"
                 android:finishOnCloseSystemDialogs="true"
                 android:theme="@style/Theme.NoDisplay"
diff --git a/core/res/res/layout/accessibility_button_chooser.xml b/core/res/res/layout/accessibility_button_chooser.xml
new file mode 100644
index 0000000..0ef785f
--- /dev/null
+++ b/core/res/res/layout/accessibility_button_chooser.xml
@@ -0,0 +1,76 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+/*
+* Copyright 2017, 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.
+*/
+-->
+<com.android.internal.widget.ResolverDrawerLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:maxWidth="@dimen/resolver_max_width"
+    android:maxCollapsedHeight="256dp"
+    android:maxCollapsedHeightSmall="56dp"
+    android:id="@id/contentPanel">
+
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:orientation="vertical"
+        android:background="?attr/colorBackground"
+        android:paddingTop="8dp"
+        android:paddingBottom="8dp">
+
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:minHeight="56dp"
+            android:textAppearance="?attr/textAppearanceMedium"
+            android:text="@string/accessibility_button_prompt_text"
+            android:gravity="start|center_vertical"
+            android:layout_alignParentStart="true"
+            android:paddingStart="?attr/dialogPreferredPadding"
+            android:paddingEnd="?attr/dialogPreferredPadding"
+            android:paddingTop="8dp"
+            android:paddingBottom="8dp"/>
+
+        <GridView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:id="@+id/accessibility_button_chooser_grid"
+            android:columnWidth="90dp"
+            android:numColumns="auto_fit"
+            android:verticalSpacing="10dp"
+            android:horizontalSpacing="10dp"
+            android:stretchMode="columnWidth"
+            android:paddingStart="?attr/dialogPreferredPadding"
+            android:paddingEnd="?attr/dialogPreferredPadding"
+            android:gravity="center"/>
+
+        <TextView
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:id="@+id/accessibility_button_prompt"
+            android:layout_alwaysShow="true"
+            android:textAppearance="?attr/textAppearanceMedium"
+            android:text="@string/accessibility_button_instructional_text"
+            android:gravity="start|center_vertical"
+            android:paddingStart="?attr/dialogPreferredPadding"
+            android:paddingEnd="?attr/dialogPreferredPadding"
+            android:paddingTop="8dp"
+            android:paddingBottom="8dp"
+            android:visibility="gone"/>
+    </LinearLayout>
+</com.android.internal.widget.ResolverDrawerLayout>
diff --git a/core/res/res/layout/accessibility_button_chooser_item.xml b/core/res/res/layout/accessibility_button_chooser_item.xml
new file mode 100644
index 0000000..76a9308
--- /dev/null
+++ b/core/res/res/layout/accessibility_button_chooser_item.xml
@@ -0,0 +1,52 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+/*
+** Copyright 2017, 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.
+*/
+-->
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+              android:orientation="vertical"
+              android:layout_width="wrap_content"
+              android:layout_height="wrap_content"
+              android:minWidth="80dp"
+              android:gravity="center"
+              android:paddingTop="8dp"
+              android:paddingBottom="8dp"
+              android:background="?attr/selectableItemBackgroundBorderless">
+
+    <ImageView android:id="@+id/accessibility_button_target_icon"
+               android:layout_width="48dp"
+               android:layout_height="48dp"
+               android:layout_marginLeft="3dp"
+               android:layout_marginRight="3dp"
+               android:layout_marginBottom="3dp"
+               android:scaleType="fitCenter"/>
+
+    <TextView android:id="@+id/accessibility_button_target_label"
+              android:layout_width="wrap_content"
+              android:layout_height="wrap_content"
+              android:layout_marginTop="8dp"
+              android:layout_marginLeft="4dp"
+              android:layout_marginRight="4dp"
+              android:textAppearance="?attr/textAppearanceSmall"
+              android:textColor="?attr/textColorPrimary"
+              android:textSize="12sp"
+              android:fontFamily="sans-serif-condensed"
+              android:gravity="top|center_horizontal"
+              android:minLines="2"
+              android:maxLines="2"
+              android:ellipsize="marquee"/>
+</LinearLayout>
+
diff --git a/core/res/res/values/strings.xml b/core/res/res/values/strings.xml
index 566ba02..868e256 100644
--- a/core/res/res/values/strings.xml
+++ b/core/res/res/values/strings.xml
@@ -3958,6 +3958,15 @@
     <string name="accessibility_shortcut_disabling_service">Accessibility Shortcut turned
         <xliff:g id="service_name" example="TalkBack">%1$s</xliff:g> off</string>
 
+    <!-- Text appearing in a prompt at the top of UI allowing the user to select a target service or feature to be assigned to the Accessibility button in the navigation bar. -->
+    <string name="accessibility_button_prompt_text">Choose a feature to use when you tap the Accessibility button:</string>
+
+    <!-- Text describing how to display UI allowing a user to select a target service or feature to be assigned to the Accessibility button in the navigation bar. -->
+    <string name="accessibility_button_instructional_text">To change features, touch &amp; hold the Accessibility button.</string>
+
+    <!-- Text used to describe system navigation features, shown within a UI allowing a user to assign system magnification features to the Accessibility button in the navigation bar. -->
+    <string name="accessibility_magnification_chooser_text">Magnification</string>
+
     <!-- Text spoken when the current user is switched if accessibility is enabled. [CHAR LIMIT=none] -->
     <string name="user_switched">Current user <xliff:g id="name" example="Bob">%1$s</xliff:g>.</string>
     <!-- Message shown when switching to a user [CHAR LIMIT=none] -->
diff --git a/core/res/res/values/symbols.xml b/core/res/res/values/symbols.xml
index f4d490a..b23c96c 100644
--- a/core/res/res/values/symbols.xml
+++ b/core/res/res/values/symbols.xml
@@ -2841,6 +2841,15 @@
   <java-symbol type="string" name="leave_accessibility_shortcut_on" />
   <java-symbol type="string" name="config_defaultAccessibilityService" />
 
+  <!-- Accessibility Button -->
+  <java-symbol type="layout" name="accessibility_button_chooser" />
+  <java-symbol type="layout" name="accessibility_button_chooser_item" />
+  <java-symbol type="id" name="accessibility_button_chooser_grid" />
+  <java-symbol type="id" name="accessibility_button_prompt" />
+  <java-symbol type="id" name="accessibility_button_target_icon" />
+  <java-symbol type="id" name="accessibility_button_target_label" />
+  <java-symbol type="string" name="accessibility_magnification_chooser_text" />
+
   <!-- com.android.internal.widget.RecyclerView -->
   <java-symbol type="id" name="item_touch_helper_previous_elevation"/>
   <java-symbol type="dimen" name="item_touch_helper_max_drag_scroll_per_frame"/>
diff --git a/packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarFragment.java b/packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarFragment.java
index 5fb642f..1f03024 100644
--- a/packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarFragment.java
+++ b/packages/SystemUI/src/com/android/systemui/statusbar/phone/NavigationBarFragment.java
@@ -557,9 +557,9 @@
     }
 
     private boolean onAccessibilityLongClick(View v) {
-        // TODO(b/34720082): Target service selection via long click
-        android.widget.Toast.makeText(getContext(), "Service selection coming soon...",
-                android.widget.Toast.LENGTH_LONG).show();
+        Intent intent = new Intent(AccessibilityManager.ACTION_CHOOSE_ACCESSIBILITY_BUTTON);
+        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
+        v.getContext().startActivity(intent);
         return true;
     }
 
diff --git a/services/accessibility/java/com/android/server/accessibility/AccessibilityManagerService.java b/services/accessibility/java/com/android/server/accessibility/AccessibilityManagerService.java
index 3666763..05c6592 100644
--- a/services/accessibility/java/com/android/server/accessibility/AccessibilityManagerService.java
+++ b/services/accessibility/java/com/android/server/accessibility/AccessibilityManagerService.java
@@ -70,6 +70,7 @@
 import android.os.UserManager;
 import android.os.UserManagerInternal;
 import android.provider.Settings;
+import android.provider.SettingsStringUtil;
 import android.provider.SettingsStringUtil.ComponentNameSet;
 import android.provider.SettingsStringUtil.SettingStringHelper;
 import android.text.TextUtils;
@@ -100,7 +101,6 @@
 import com.android.internal.R;
 import com.android.internal.annotations.GuardedBy;
 import com.android.internal.content.PackageMonitor;
-import com.android.internal.os.HandlerCaller;
 import com.android.internal.os.SomeArgs;
 import com.android.internal.util.IntPair;
 import com.android.server.LocalServices;
@@ -1154,17 +1154,55 @@
 
     private void notifyAccessibilityButtonClickedLocked() {
         final UserState state = getCurrentUserStateLocked();
-        if (state.mIsNavBarMagnificationEnabled) {
-            mMainHandler.obtainMessage(
-                    MainHandler.MSG_SEND_ACCESSIBILITY_BUTTON_TO_INPUT_FILTER).sendToTarget();
-        } else {
-            for (int i = state.mBoundServices.size() - 1; i >= 0; i--) {
-                final Service service = state.mBoundServices.get(i);
-                // TODO(b/34720082): Only notify a single user-defined service
-                if (service.mRequestAccessibilityButton) {
-                    service.notifyAccessibilityButtonClickedLocked();
+
+        int potentialTargets = state.mIsNavBarMagnificationEnabled ? 1 : 0;
+        for (int i = state.mBoundServices.size() - 1; i >= 0; i--) {
+            final Service service = state.mBoundServices.get(i);
+            if (service.mRequestAccessibilityButton) {
+                potentialTargets++;
+            }
+        }
+
+        if (potentialTargets == 0) {
+            return;
+        }
+        if (potentialTargets == 1) {
+            if (state.mIsNavBarMagnificationEnabled) {
+                mMainHandler.obtainMessage(
+                        MainHandler.MSG_SEND_ACCESSIBILITY_BUTTON_TO_INPUT_FILTER).sendToTarget();
+                return;
+            } else {
+                for (int i = state.mBoundServices.size() - 1; i >= 0; i--) {
+                    final Service service = state.mBoundServices.get(i);
+                    if (service.mRequestAccessibilityButton) {
+                        service.notifyAccessibilityButtonClickedLocked();
+                        return;
+                    }
                 }
             }
+        } else {
+            if (state.mServiceAssignedToAccessibilityButton == null
+                    && !state.mIsNavBarMagnificationAssignedToAccessibilityButton) {
+                mMainHandler.obtainMessage(
+                        MainHandler.MSG_SHOW_ACCESSIBILITY_BUTTON_CHOOSER).sendToTarget();
+            } else if (state.mIsNavBarMagnificationEnabled
+                    && state.mIsNavBarMagnificationAssignedToAccessibilityButton) {
+                mMainHandler.obtainMessage(
+                        MainHandler.MSG_SEND_ACCESSIBILITY_BUTTON_TO_INPUT_FILTER).sendToTarget();
+                return;
+            } else {
+                for (int i = state.mBoundServices.size() - 1; i >= 0; i--) {
+                    final Service service = state.mBoundServices.get(i);
+                    if (service.mRequestAccessibilityButton && (service.mComponentName.equals(
+                            state.mServiceAssignedToAccessibilityButton))) {
+                        service.notifyAccessibilityButtonClickedLocked();
+                        return;
+                    }
+                }
+            }
+            // The user may have turned off the assigned service or feature
+            mMainHandler.obtainMessage(
+                    MainHandler.MSG_SHOW_ACCESSIBILITY_BUTTON_CHOOSER).sendToTarget();
         }
     }
 
@@ -1534,6 +1572,12 @@
         }
     }
 
+    private void showAccessibilityButtonTargetSelection() {
+        Intent intent = new Intent(AccessibilityManager.ACTION_CHOOSE_ACCESSIBILITY_BUTTON);
+        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
+        mContext.startActivity(intent);
+    }
+
     private void scheduleNotifyClientsOfServicesStateChange(UserState userState) {
         mMainHandler.obtainMessage(MainHandler.MSG_SEND_SERVICES_STATE_CHANGED_TO_CLIENTS,
                 userState.mUserId).sendToTarget();
@@ -1681,6 +1725,7 @@
         scheduleUpdateInputFilter(userState);
         scheduleUpdateClientsIfNeededLocked(userState);
         updateRelevantEventsLocked(userState);
+        updateAccessibilityButtonTargets(userState);
     }
 
     private void updateAccessibilityFocusBehaviorLocked(UserState userState) {
@@ -1794,6 +1839,7 @@
         somethingChanged |= readMagnificationEnabledSettingsLocked(userState);
         somethingChanged |= readAutoclickEnabledSettingLocked(userState);
         somethingChanged |= readAccessibilityShortcutSettingLocked(userState);
+        somethingChanged |= readAccessibilityButtonSettingsLocked(userState);
         return somethingChanged;
     }
 
@@ -1928,6 +1974,37 @@
         return true;
     }
 
+    private boolean readAccessibilityButtonSettingsLocked(UserState userState) {
+        String componentId = Settings.Secure.getStringForUser(mContext.getContentResolver(),
+                Settings.Secure.ACCESSIBILITY_BUTTON_TARGET_COMPONENT, userState.mUserId);
+        if (TextUtils.isEmpty(componentId)) {
+            if ((userState.mServiceAssignedToAccessibilityButton == null)
+                    && !userState.mIsNavBarMagnificationAssignedToAccessibilityButton) {
+                return false;
+            }
+            userState.mServiceAssignedToAccessibilityButton = null;
+            userState.mIsNavBarMagnificationAssignedToAccessibilityButton = false;
+            return true;
+        }
+
+        if (componentId.equals(MagnificationController.class.getName())) {
+            if (userState.mIsNavBarMagnificationAssignedToAccessibilityButton) {
+                return false;
+            }
+            userState.mServiceAssignedToAccessibilityButton = null;
+            userState.mIsNavBarMagnificationAssignedToAccessibilityButton = true;
+            return true;
+        }
+
+        ComponentName componentName = ComponentName.unflattenFromString(componentId);
+        if (componentName.equals(userState.mServiceAssignedToAccessibilityButton)) {
+            return false;
+        }
+        userState.mServiceAssignedToAccessibilityButton = componentName;
+        userState.mIsNavBarMagnificationAssignedToAccessibilityButton = false;
+        return true;
+    }
+
     /**
      * Check if the service that will be enabled by the shortcut is installed. If it isn't,
      * clear the value and the associated setting so a sideloaded service can't spoof the
@@ -2138,6 +2215,22 @@
         }
     }
 
+    private void updateAccessibilityButtonTargets(UserState userState) {
+        final List<Service> services;
+        synchronized (mLock) {
+            services = userState.mBoundServices;
+            int numServices = services.size();
+            for (int i = 0; i < numServices; i++) {
+                final Service service = services.get(i);
+                if (service.mRequestAccessibilityButton) {
+                    boolean available = service.mComponentName.equals(
+                            userState.mServiceAssignedToAccessibilityButton);
+                    service.notifyAccessibilityButtonAvailabilityChangedLocked(available);
+                }
+            }
+        }
+    }
+
     @GuardedBy("mLock")
     private MagnificationSpec getCompatibleMagnificationSpecLocked(int windowId) {
         IBinder windowToken = mGlobalWindowTokens.get(windowId);
@@ -2212,7 +2305,7 @@
      * Disables accessibility service specified by {@param componentName} for the {@param userId}.
      */
     private void disableAccessibilityServiceLocked(ComponentName componentName, int userId) {
-        final SettingStringHelper setting =
+        final SettingsStringUtil.SettingStringHelper setting =
                 new SettingStringHelper(
                         mContext.getContentResolver(),
                         Settings.Secure.ENABLED_ACCESSIBILITY_SERVICES,
@@ -2342,6 +2435,7 @@
         public static final int MSG_UPDATE_FINGERPRINT = 11;
         public static final int MSG_SEND_RELEVANT_EVENTS_CHANGED_TO_CLIENTS = 12;
         public static final int MSG_SEND_ACCESSIBILITY_BUTTON_TO_INPUT_FILTER = 13;
+        public static final int MSG_SHOW_ACCESSIBILITY_BUTTON_CHOOSER = 14;
 
         public MainHandler(Looper looper) {
             super(looper);
@@ -2435,6 +2529,10 @@
                             mInputFilter.notifyAccessibilityButtonClicked();
                         }
                     }
+                } break;
+
+                case MSG_SHOW_ACCESSIBILITY_BUTTON_CHOOSER: {
+                    showAccessibilityButtonTargetSelection();
                 }
             }
         }
@@ -4813,6 +4911,8 @@
         public int mSoftKeyboardShowMode = 0;
 
         public boolean mIsAccessibilityButtonAvailable;
+        public boolean mIsNavBarMagnificationAssignedToAccessibilityButton;
+        public ComponentName mServiceAssignedToAccessibilityButton;
 
         public boolean mIsTouchExplorationEnabled;
         public boolean mIsTextHighContrastEnabled;
@@ -4888,6 +4988,8 @@
             mIsEnhancedWebAccessibilityEnabled = false;
             mIsDisplayMagnificationEnabled = false;
             mIsNavBarMagnificationEnabled = false;
+            mServiceAssignedToAccessibilityButton = null;
+            mIsNavBarMagnificationAssignedToAccessibilityButton = false;
             mIsAutoclickEnabled = false;
             mSoftKeyboardShowMode = 0;
 
@@ -4953,6 +5055,9 @@
         private final Uri mAccessibilityShortcutServiceIdUri = Settings.Secure.getUriFor(
                 Settings.Secure.ACCESSIBILITY_SHORTCUT_TARGET_SERVICE);
 
+        private final Uri mAccessibilityButtonComponentIdUri = Settings.Secure.getUriFor(
+                Settings.Secure.ACCESSIBILITY_BUTTON_TARGET_COMPONENT);
+
         public AccessibilityContentObserver(Handler handler) {
             super(handler);
         }
@@ -4985,6 +5090,8 @@
                     mAccessibilitySoftKeyboardModeUri, false, this, UserHandle.USER_ALL);
             contentResolver.registerContentObserver(
                     mAccessibilityShortcutServiceIdUri, false, this, UserHandle.USER_ALL);
+            contentResolver.registerContentObserver(
+                    mAccessibilityButtonComponentIdUri, false, this, UserHandle.USER_ALL);
         }
 
         @Override
@@ -5042,6 +5149,10 @@
                     if (readAccessibilityShortcutSettingLocked(userState)) {
                         onUserStateChangedLocked(userState);
                     }
+                } else if (mAccessibilityButtonComponentIdUri.equals(uri)) {
+                    if (readAccessibilityButtonSettingsLocked(userState)) {
+                        onUserStateChangedLocked(userState);
+                    }
                 }
             }
         }