Fireperf fragments: lifecycle callbacks

firebase-perf/src/main/java/com/google/firebase/perf/application/AppStateMonitor.java

@@ -22,6 +22,7 @@
 import android.util.SparseIntArray;
 import androidx.annotation.NonNull;
 import androidx.core.app.FrameMetricsAggregator;
+import androidx.fragment.app.FragmentActivity;
 import com.google.android.gms.common.util.VisibleForTesting;
 import com.google.firebase.perf.config.ConfigResolver;
 import com.google.firebase.perf.logging.AndroidLogger;
@@ -140,7 +141,19 @@ public void incrementTsnsCount(int value) {
   }
 
   @Override
-  public void onActivityCreated(Activity activity, Bundle savedInstanceState) {}
+  public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
+    if (isScreenTraceSupported(activity) && configResolver.isPerformanceMonitoringEnabled()) {
+      if (activity instanceof FragmentActivity) {
+        FragmentActivity fragmentActivity = (FragmentActivity) activity;
+        fragmentActivity
+            .getSupportFragmentManager()
+            .registerFragmentLifecycleCallbacks(
+                new FragmentStateMonitor(
+                    fragmentActivity, clock, transportManager, this, frameMetricsAggregator),
+                true);
+      }
+    }
+  }
 
   @Override
   public void onActivityDestroyed(Activity activity) {}

firebase-perf/src/main/java/com/google/firebase/perf/application/FragmentStateMonitor.java

@@ -0,0 +1,71 @@
+// Copyright 2022 Google LLC
+//
+// 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.google.firebase.perf.application;
+
+import androidx.annotation.NonNull;
+import androidx.core.app.FrameMetricsAggregator;
+import androidx.fragment.app.Fragment;
+import androidx.fragment.app.FragmentActivity;
+import androidx.fragment.app.FragmentManager;
+import com.google.firebase.perf.logging.AndroidLogger;
+import com.google.firebase.perf.transport.TransportManager;
+import com.google.firebase.perf.util.Clock;
+import com.google.firebase.perf.util.Constants;
+
+public class FragmentStateMonitor extends FragmentManager.FragmentLifecycleCallbacks {
+  private static final AndroidLogger logger = AndroidLogger.getInstance();
+  private final FragmentActivity activity;
+  private final Clock clock;
+  private final TransportManager transportManager;
+  private final AppStateMonitor appStateMonitor;
+  private final FrameMetricsAggregator frameMetricsAggregator;
+
+  public FragmentStateMonitor(
+      FragmentActivity activity,
+      Clock clock,
+      TransportManager transportManager,
+      AppStateMonitor appStateMonitor,
+      FrameMetricsAggregator fma) {
+    this.activity = activity;
+    this.clock = clock;
+    this.transportManager = transportManager;
+    this.appStateMonitor = appStateMonitor;
+    this.frameMetricsAggregator = fma;
+  }
+
+  /**
+   * Fragment screen trace name is prefix "_st_" concatenates with Fragment's class name.
+   *
+   * @param fragment fragment object.
+   * @return Fragment screen trace name.
+   */
+  public static String getFragmentScreenTraceName(Fragment fragment) {
+    return Constants.SCREEN_TRACE_PREFIX + fragment.getClass().getSimpleName();
+  }
+
+  @Override
+  public void onFragmentResumed(@NonNull FragmentManager fm, @NonNull Fragment f) {
+    super.onFragmentResumed(fm, f);
+    // Start Fragment screen trace
+    logger.debug("FragmentMonitor %s.onFragmentResumed", f.getClass().getSimpleName());
+  }
+
+  @Override
+  public void onFragmentPaused(@NonNull FragmentManager fm, @NonNull Fragment f) {
+    super.onFragmentPaused(fm, f);
+    // Stop Fragment screen trace
+    logger.debug("FragmentMonitor %s.onFragmentPaused ", f.getClass().getSimpleName());
+  }
+}