一步步拆解 LeakCanary(3)

接下来，我们一起来看一下 ActivityRefWatcher.install 方法

ActivityRefWatcher.install((Application) context, refWatcher);

public final class ActivityRefWatcher {

  /** @deprecated Use {@link #install(Application, RefWatcher)}. */
  @Deprecated
  public static void installOnIcsPlus(Application application, RefWatcher refWatcher) {
    install(application, refWatcher);
  }

  public static void install(Application application, RefWatcher refWatcher) {
    new ActivityRefWatcher(application, refWatcher).watchActivities();
  }

  private final Application.ActivityLifecycleCallbacks lifecycleCallbacks =
      new Application.ActivityLifecycleCallbacks() {
        @Override 
        public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
        }

        @Override 
        public void onActivityStarted(Activity activity) {
        }

        @Override 
        public void onActivityResumed(Activity activity) {
        }

        @Override 
        public void onActivityPaused(Activity activity) {
        }

        @Override 
        public void onActivityStopped(Activity activity) {
        }

        @Override 
        public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
        }

        @Override 
        public void onActivityDestroyed(Activity activity) {
          ActivityRefWatcher.this.onActivityDestroyed(activity);
        }
      };

  private final Application application;
  private final RefWatcher refWatcher;

  /**
   * Constructs an {@link ActivityRefWatcher} that will make sure the activities are not leaking
   * after they have been destroyed.
   */
  public ActivityRefWatcher(Application application, RefWatcher refWatcher) {
    this.application = checkNotNull(application, "application");
    this.refWatcher = checkNotNull(refWatcher, "refWatcher");
  }

  void onActivityDestroyed(Activity activity) {
    refWatcher.watch(activity);
  }

  public void watchActivities() {
    // Make sure you don"t get installed twice.
    stopWatchingActivities();
    application.registerActivityLifecycleCallbacks(lifecycleCallbacks);
  }

  public void stopWatchingActivities() {
    application.unregisterActivityLifecycleCallbacks(lifecycleCallbacks);
  }
}

install 来说，主要做以下事情