diff --git a/native/android/Android.bp b/native/android/Android.bp
index 7793d6c..6db4da9 100644
--- a/native/android/Android.bp
+++ b/native/android/Android.bp
@@ -36,6 +36,7 @@
     defaults: ["libandroid_defaults"],
 
     srcs: [
+        "activity_manager.cpp",
         "asset_manager.cpp",
         "choreographer.cpp",
         "configuration.cpp",
@@ -95,6 +96,10 @@
 
     include_dirs: ["bionic/libc/dns/include"],
 
+    local_include_dirs: [ "include_platform", ],
+
+    export_include_dirs: [ "include_platform", ],
+
     version_script: "libandroid.map.txt",
     stubs: {
         symbol_file: "libandroid.map.txt",
diff --git a/native/android/activity_manager.cpp b/native/android/activity_manager.cpp
new file mode 100644
index 0000000..82f4569
--- /dev/null
+++ b/native/android/activity_manager.cpp
@@ -0,0 +1,226 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#define LOG_NDEBUG 0
+#define LOG_TAG "AActivityManager"
+#include <utils/Log.h>
+
+#include <android/activity_manager.h>
+#include <binder/ActivityManager.h>
+
+namespace android {
+namespace activitymanager {
+
+// Global instance of ActivityManager, service is obtained only on first use.
+static ActivityManager gAm;
+// String tag used with ActivityManager.
+static const String16& getTag() {
+    static String16 tag("libandroid");
+    return tag;
+}
+
+struct UidObserver : public BnUidObserver, public virtual IBinder::DeathRecipient {
+    explicit UidObserver(const AActivityManager_onUidImportance& cb,
+                         int32_t cutpoint, void* cookie)
+          : mCallback(cb), mImportanceCutpoint(cutpoint), mCookie(cookie), mRegistered(false) {}
+    bool registerSelf();
+    void unregisterSelf();
+
+    // IUidObserver
+    void onUidGone(uid_t uid, bool disabled) override;
+    void onUidActive(uid_t uid) override;
+    void onUidIdle(uid_t uid, bool disabled) override;
+    void onUidStateChanged(uid_t uid, int32_t procState, int64_t procStateSeq,
+                           int32_t capability) override;
+
+    // IBinder::DeathRecipient implementation
+    void binderDied(const wp<IBinder>& who) override;
+
+    static int32_t procStateToImportance(int32_t procState);
+    static int32_t importanceToProcState(int32_t importance);
+
+    AActivityManager_onUidImportance mCallback;
+    int32_t mImportanceCutpoint;
+    void* mCookie;
+    std::mutex mRegisteredLock;
+    bool mRegistered GUARDED_BY(mRegisteredLock);
+};
+
+//static
+int32_t UidObserver::procStateToImportance(int32_t procState) {
+    // TODO: remove this after adding Importance to onUidStateChanged callback.
+    if (procState == ActivityManager::PROCESS_STATE_NONEXISTENT) {
+        return AACTIVITYMANAGER_IMPORTANCE_GONE;
+    } else if (procState >= ActivityManager::PROCESS_STATE_HOME) {
+        return AACTIVITYMANAGER_IMPORTANCE_CACHED;
+    } else if (procState == ActivityManager::PROCESS_STATE_HEAVY_WEIGHT) {
+        return AACTIVITYMANAGER_IMPORTANCE_CANT_SAVE_STATE;
+    } else if (procState >= ActivityManager::PROCESS_STATE_TOP_SLEEPING) {
+        return AACTIVITYMANAGER_IMPORTANCE_TOP_SLEEPING;
+    } else if (procState >= ActivityManager::PROCESS_STATE_SERVICE) {
+        return AACTIVITYMANAGER_IMPORTANCE_SERVICE;
+    } else if (procState >= ActivityManager::PROCESS_STATE_TRANSIENT_BACKGROUND) {
+        return AACTIVITYMANAGER_IMPORTANCE_PERCEPTIBLE;
+    } else if (procState >= ActivityManager::PROCESS_STATE_IMPORTANT_FOREGROUND) {
+        return AACTIVITYMANAGER_IMPORTANCE_VISIBLE;
+    } else if (procState >= ActivityManager::PROCESS_STATE_FOREGROUND_SERVICE) {
+        return AACTIVITYMANAGER_IMPORTANCE_FOREGROUND_SERVICE;
+    } else {
+        return AACTIVITYMANAGER_IMPORTANCE_FOREGROUND;
+    }
+}
+
+//static
+int32_t UidObserver::importanceToProcState(int32_t importance) {
+    // TODO: remove this after adding Importance to onUidStateChanged callback.
+    if (importance == AACTIVITYMANAGER_IMPORTANCE_GONE) {
+        return ActivityManager::PROCESS_STATE_NONEXISTENT;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_CACHED) {
+        return ActivityManager::PROCESS_STATE_HOME;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_CANT_SAVE_STATE) {
+        return ActivityManager::PROCESS_STATE_HEAVY_WEIGHT;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_TOP_SLEEPING) {
+        return ActivityManager::PROCESS_STATE_TOP_SLEEPING;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_SERVICE) {
+        return ActivityManager::PROCESS_STATE_SERVICE;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_PERCEPTIBLE) {
+        return ActivityManager::PROCESS_STATE_TRANSIENT_BACKGROUND;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_VISIBLE) {
+        return ActivityManager::PROCESS_STATE_IMPORTANT_FOREGROUND;
+    } else if (importance >= AACTIVITYMANAGER_IMPORTANCE_FOREGROUND_SERVICE) {
+        return ActivityManager::PROCESS_STATE_FOREGROUND_SERVICE;
+    } else {
+        return ActivityManager::PROCESS_STATE_TOP;
+    }
+}
+
+
+void UidObserver::onUidGone(uid_t uid, bool disabled __unused) {
+    std::scoped_lock lock{mRegisteredLock};
+
+    if (mRegistered && mCallback) {
+        mCallback(uid, AACTIVITYMANAGER_IMPORTANCE_GONE, mCookie);
+    }
+}
+
+void UidObserver::onUidActive(uid_t uid __unused) {}
+
+void UidObserver::onUidIdle(uid_t uid __unused, bool disabled __unused) {}
+
+void UidObserver::onUidStateChanged(uid_t uid, int32_t procState,
+                                    int64_t procStateSeq __unused,
+                                    int32_t capability __unused) {
+    std::scoped_lock lock{mRegisteredLock};
+
+    if (mRegistered && mCallback) {
+        mCallback(uid, procStateToImportance(procState), mCookie);
+    }
+}
+
+void UidObserver::binderDied(const wp<IBinder>& /*who*/) {
+    // ActivityManager is dead, try to re-register.
+    {
+        std::scoped_lock lock{mRegisteredLock};
+        // If client already unregistered, don't try to re-register.
+        if (!mRegistered) {
+            return;
+        }
+        // Clear mRegistered to re-register.
+        mRegistered = false;
+    }
+    registerSelf();
+}
+
+bool UidObserver::registerSelf() {
+    std::scoped_lock lock{mRegisteredLock};
+    if (mRegistered) {
+        return true;
+    }
+
+    status_t res = gAm.linkToDeath(this);
+    if (res != OK) {
+        ALOGE("UidObserver: Failed to linkToDeath with ActivityManager (err %d)", res);
+        return false;
+    }
+
+    // TODO: it seems only way to get all changes is to set cutoff to PROCESS_STATE_UNKNOWN.
+    // But there is no equivalent of PROCESS_STATE_UNKNOWN in the UidImportance.
+    // If mImportanceCutpoint is < 0, use PROCESS_STATE_UNKNOWN instead.
+    res = gAm.registerUidObserver(
+            this,
+            ActivityManager::UID_OBSERVER_GONE | ActivityManager::UID_OBSERVER_PROCSTATE,
+            (mImportanceCutpoint < 0) ? ActivityManager::PROCESS_STATE_UNKNOWN
+                                      : importanceToProcState(mImportanceCutpoint),
+            getTag());
+    if (res != OK) {
+        ALOGE("UidObserver: Failed to register with ActivityManager (err %d)", res);
+        gAm.unlinkToDeath(this);
+        return false;
+    }
+
+    mRegistered = true;
+    ALOGV("UidObserver: Registered with ActivityManager");
+    return true;
+}
+
+void UidObserver::unregisterSelf() {
+    std::scoped_lock lock{mRegisteredLock};
+
+    if (mRegistered) {
+        gAm.unregisterUidObserver(this);
+        gAm.unlinkToDeath(this);
+        mRegistered = false;
+    }
+
+    ALOGV("UidObserver: Unregistered with ActivityManager");
+}
+
+} // activitymanager
+} // android
+
+using namespace android;
+using namespace activitymanager;
+
+struct AActivityManager_UidImportanceListener : public UidObserver {
+};
+
+AActivityManager_UidImportanceListener* AActivityManager_addUidImportanceListener(
+        AActivityManager_onUidImportance onUidImportance, int32_t importanceCutpoint, void* cookie) {
+    sp<UidObserver> observer(new UidObserver(onUidImportance, importanceCutpoint, cookie));
+    if (observer == nullptr || !observer->registerSelf()) {
+        return nullptr;
+    }
+    observer->incStrong((void *)AActivityManager_addUidImportanceListener);
+    return static_cast<AActivityManager_UidImportanceListener*>(observer.get());
+}
+
+void AActivityManager_removeUidImportanceListener(
+        AActivityManager_UidImportanceListener* listener) {
+    if (listener != nullptr) {
+        UidObserver* observer = static_cast<UidObserver*>(listener);
+        observer->unregisterSelf();
+        observer->decStrong((void *)AActivityManager_addUidImportanceListener);
+    }
+}
+
+bool AActivityManager_isUidActive(uid_t uid) {
+    return gAm.isUidActive(uid, getTag());
+}
+
+int32_t AActivityManager_getUidImportance(uid_t uid) {
+    return UidObserver::procStateToImportance(gAm.getUidProcessState(uid, getTag()));
+}
+
diff --git a/native/android/include_platform/android/activity_manager.h b/native/android/include_platform/android/activity_manager.h
new file mode 100644
index 0000000..0ecd56d
--- /dev/null
+++ b/native/android/include_platform/android/activity_manager.h
@@ -0,0 +1,176 @@
+/*
+ * Copyright (C) 2020 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.
+ */
+
+#ifndef __AACTIVITYMANAGER_H__
+#define __AACTIVITYMANAGER_H__
+
+#include <sys/cdefs.h>
+#include <sys/types.h>
+
+__BEGIN_DECLS
+
+struct AActivityManager_UidImportanceListener;
+typedef struct AActivityManager_UidImportanceListener AActivityManager_UidImportanceListener;
+
+/**
+ * Callback interface when Uid Importance has changed for a uid.
+ *
+ * This callback will be called on an arbitrary thread. Calls to a given listener will be
+ * serialized.
+ *
+ * @param uid the uid for which the importance has changed.
+ * @param uidImportance the new uidImportance for the uid.
+ * @cookie the same cookie when the UidImportanceListener was added.
+ *
+ * Introduced in API 31.
+ */
+typedef void (*AActivityManager_onUidImportance)(uid_t uid, int32_t uidImportance, void* cookie);
+
+/**
+ * ActivityManager Uid Importance constants.
+ *
+ * Introduced in API 31.
+ */
+enum {
+    /**
+     * Constant for Uid Importance: This process is running the
+     * foreground UI; that is, it is the thing currently at the top of the screen
+     * that the user is interacting with.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_FOREGROUND = 100,
+
+    /**
+     * Constant for Uid Importance: This process is running a foreground
+     * service, for example to perform music playback even while the user is
+     * not immediately in the app.  This generally indicates that the process
+     * is doing something the user actively cares about.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_FOREGROUND_SERVICE = 125,
+
+    /**
+     * Constant for Uid Importance: This process is running something
+     * that is actively visible to the user, though not in the immediate
+     * foreground.  This may be running a window that is behind the current
+     * foreground (so paused and with its state saved, not interacting with
+     * the user, but visible to them to some degree); it may also be running
+     * other services under the system's control that it inconsiders important.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_VISIBLE = 200,
+
+    /**
+     * Constant for Uid Importance: This process is not something the user
+     * is directly aware of, but is otherwise perceptible to them to some degree.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_PERCEPTIBLE = 230,
+
+    /**
+     * Constant for Uid Importance: This process contains services
+     * that should remain running.  These are background services apps have
+     * started, not something the user is aware of, so they may be killed by
+     * the system relatively freely (though it is generally desired that they
+     * stay running as long as they want to).
+     */
+    AACTIVITYMANAGER_IMPORTANCE_SERVICE = 300,
+
+    /**
+     * Constant for Uid Importance: This process is running the foreground
+     * UI, but the device is asleep so it is not visible to the user.  Though the
+     * system will try hard to keep its process from being killed, in all other
+     * ways we consider it a kind of cached process, with the limitations that go
+     * along with that state: network access, running background services, etc.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_TOP_SLEEPING = 325,
+
+    /**
+     * Constant for Uid Importance: This process is running an
+     * application that can not save its state, and thus can't be killed
+     * while in the background.  This will be used with apps that have
+     * {@link android.R.attr#cantSaveState} set on their application tag.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_CANT_SAVE_STATE = 350,
+
+    /**
+     * Constant for Uid Importance: This process process contains
+     * cached code that is expendable, not actively running any app components
+     * we care about.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_CACHED = 400,
+
+    /**
+     * Constant for Uid Importance: This process does not exist.
+     */
+    AACTIVITYMANAGER_IMPORTANCE_GONE = 1000,
+};
+
+#if __ANDROID_API__ >= 31
+
+/**
+ * Adds a UidImportanceListener to the ActivityManager.
+ *
+ * This API requires android.Manifest.permission.PACKAGE_USAGE_STATS permission.
+ *
+ * @param onUidImportance the listener callback that will receive change reports.
+ *
+ * @param importanceCutpoint the level of importance in which the caller is interested
+ * in differences. For example, if AACTIVITYMANAGER_IMPORTANCE_PERCEPTIBLE is used
+ * here, you will receive a call each time a uid's importance transitions between being
+ * <= AACTIVITYMANAGER_IMPORTANCE_PERCEPTIBLE and > AACTIVITYMANAGER_IMPORTANCE_PERCEPTIBLE.
+ *
+ * @param cookie a cookie that will be passed back to the listener callback.
+ *
+ * @return an opaque pointer of AActivityManager_UidImportanceListener, or nullptr
+ * upon failure. Upon success, the returned AActivityManager_UidImportanceListener pointer
+ * must be removed and released through AActivityManager_removeUidImportanceListener.
+ */
+AActivityManager_UidImportanceListener* AActivityManager_addUidImportanceListener(
+        AActivityManager_onUidImportance onUidImportance,
+        int32_t importanceCutpoint,
+        void* cookie) __INTRODUCED_IN(31);
+
+/**
+ * Removes a UidImportanceListener that was added with AActivityManager_addUidImportanceListener.
+ *
+ * When this returns, it's guaranteed the listener callback will no longer be invoked.
+ *
+ * @param listener the UidImportanceListener to be removed.
+ */
+void AActivityManager_removeUidImportanceListener(
+        AActivityManager_UidImportanceListener* listener) __INTRODUCED_IN(31);
+
+/**
+ * Queries if a uid is currently active.
+ *
+ * This API requires android.Manifest.permission.PACKAGE_USAGE_STATS permission.
+ *
+ * @return true if the uid is active, false otherwise.
+ */
+bool AActivityManager_isUidActive(uid_t uid) __INTRODUCED_IN(31);
+
+/**
+ * Queries the current Uid Importance value of a uid.
+ *
+ * This API requires android.Manifest.permission.PACKAGE_USAGE_STATS permission.
+ *
+ * @param uid the uid for which the importance value is queried.
+ * @return the current uid importance value for uid.
+ */
+int32_t AActivityManager_getUidImportance(uid_t uid) __INTRODUCED_IN(31);
+
+#endif // __ANDROID_API__ >= 31
+
+__END_DECLS
+
+#endif  // __AACTIVITYMANAGER_H__
diff --git a/native/android/libandroid.map.txt b/native/android/libandroid.map.txt
index 3027eac..5b6039c 100644
--- a/native/android/libandroid.map.txt
+++ b/native/android/libandroid.map.txt
@@ -1,5 +1,9 @@
 LIBANDROID {
   global:
+    AActivityManager_addUidImportanceListener; # apex # introduced=31
+    AActivityManager_removeUidImportanceListener; # apex # introduced=31
+    AActivityManager_isUidActive; # apex # introduced=31
+    AActivityManager_getUidImportance; # apex # introduced=31
     AAssetDir_close;
     AAssetDir_getNextFileName;
     AAssetDir_rewind;