在Application中初始化

LeakCanary.install(this);

使用build设计模式，创建RefWatcher对象

public static @NonNull RefWatcher install(@NonNull Application application) {
return refWatcher(application).listenerServiceClass(DisplayLeakService.class)
    .excludedRefs(AndroidExcludedRefs.createAppDefaults().build())
    .buildAndInstall();
}

设置heap监听 ServiceHeapDumpListener

public @NonNull AndroidRefWatcherBuilder   listenerServiceClass(
  @NonNull Class<? extends AbstractAnalysisResultService> listenerServiceClass) {
 enableDisplayLeakActivity =   DisplayLeakService.class.isAssignableFrom(listenerServiceClass);
 return heapDumpListener(new ServiceHeapDumpListener(context, listenerServiceClass));
 }
 
 
 public @NonNull RefWatcher buildAndInstall() {
if (LeakCanaryInternals.installedRefWatcher != null) {
  throw new UnsupportedOperationException("buildAndInstall() should only be called once.");
}
RefWatcher refWatcher = build();
if (refWatcher != DISABLED) {
  if (enableDisplayLeakActivity) {
    LeakCanaryInternals.setEnabledAsync(context, DisplayLeakActivity.class, true);
  }
  //观察activity
  if (watchActivities) {
    ActivityRefWatcher.install(context, refWatcher);
  }
  //观察fragment
  if (watchFragments) {
    FragmentRefWatcher.Helper.install(context, refWatcher);
  }
}
LeakCanaryInternals.installedRefWatcher = refWatcher;
return refWatcher;
}
在ActivityRefWatcher 中，处理activity引用观察情况

//观察activity
public static void install(@NonNull Context context, @NonNull RefWatcher refWatcher) {
Application application = (Application) context.getApplicationContext();
//创建activity引用观察类
ActivityRefWatcher activityRefWatcher = new ActivityRefWatcher(application, refWatcher);
//activity生命周期回调
application.registerActivityLifecycleCallbacks(activityRefWatcher.lifecycleCallbacks);
}

接下来看activity回调

private final Application.ActivityLifecycleCallbacks lifecycleCallbacks =
  new ActivityLifecycleCallbacksAdapter() {
    @Override public void onActivityDestroyed(Activity activity) {
    //在onDestroy中添加观察
      refWatcher.watch(activity);
    }
  };

调用RefWatcher中 watch

public void watch(Object watchedReference, String referenceName) {
...
final long watchStartNanoTime = System.nanoTime();
String key = UUID.randomUUID().toString();
//保存一个随机key，用于判断当前对象是否被回收
retainedKeys.add(key);
//把activity放到弱引用池中
final KeyedWeakReference reference =
    new KeyedWeakReference(watchedReference, key, referenceName, queue);
    
ensureGoneAsync(watchStartNanoTime, reference);
}
RefWatcher.ensureGoneAsync方法中会调用ensureGone(reference, watchStartNanoTime); 所以接下来看这个方法

Retryable.Result ensureGone(final KeyedWeakReference reference, final long watchStartNanoTime) {
long gcStartNanoTime = System.nanoTime();
long watchDurationMs = NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);
//移除引用池中key
removeWeaklyReachableReferences();

if (debuggerControl.isDebuggerAttached()) {
  // The debugger can create false leaks.
  return RETRY;
}
//判断此引用是否还存在
if (gone(reference)) {
  return DONE;
}
//出发gc
gcTrigger.runGc();
//再次移除
removeWeaklyReachableReferences();
//此引用还存在，说明此引用还未回收，存在内存泄漏的风险
if (!gone(reference)) {
  long startDumpHeap = System.nanoTime();
  long gcDurationMs = NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime);
 //生成hprof文件 AndroidHeapDumper 文件路径 File downloadsDirectory = Environment.getExternalStoragePublicDirectory(DIRECTORY_DOWNLOADS);
 //Debug.dumpHprofData(heapDumpFile.getAbsolutePath());
  File heapDumpFile = heapDumper.dumpHeap();
  if (heapDumpFile == RETRY_LATER) {
    // Could not dump the heap.
    return RETRY;
  }
  long heapDumpDurationMs = NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap);
    
  HeapDump heapDump = heapDumpBuilder.heapDumpFile(heapDumpFile).referenceKey(reference.key)
      .referenceName(reference.name)
      .watchDurationMs(watchDurationMs)
      .gcDurationMs(gcDurationMs)
      .heapDumpDurationMs(heapDumpDurationMs)
      .build();
 //堆内存分析
  heapdumpListener.analyze(heapDump);
}
return DONE;
}

ServiceHeapDumpListener 中analyze方法会调用 HeapAnalyzerService.runAnalysis(context, heapDump, listenerServiceClass); 创建一个服务HeapAnalyzerService来分析

public static void runAnalysis(Context context, HeapDump heapDump,
  Class<? extends AbstractAnalysisResultService> listenerServiceClass) {
setEnabledBlocking(context, HeapAnalyzerService.class, true);
setEnabledBlocking(context, listenerServiceClass, true);
Intent intent = new Intent(context, HeapAnalyzerService.class);
intent.putExtra(LISTENER_CLASS_EXTRA, listenerServiceClass.getName());
intent.putExtra(HEAPDUMP_EXTRA, heapDump);
ContextCompat.startForegroundService(context, intent);
 }
 //在onHandleIntent调用
 @Override protected void onHandleIntentInForeground(@Nullable Intent intent) {
 ...
 String listenerClassName =  intent.getStringExtra(LISTENER_CLASS_EXTRA);
 HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAPDUMP_EXTRA);
//核心类，堆内存
HeapAnalyzer heapAnalyzer =
    new HeapAnalyzer(heapDump.excludedRefs, this, heapDump.reachabilityInspectorClasses);

AnalysisResult result = heapAnalyzer.checkForLeak(heapDump.heapDumpFile, heapDump.referenceKey,
    heapDump.computeRetainedHeapSize);
AbstractAnalysisResultService.sendResultToListener(this, listenerClassName, heapDump, result);
}