LeakCanary 是由 Square 开源的针对 Android 和 Java 的内存泄漏检测工具。

使用

LeakCanary 的集成过程很简单，首先在 build.gradle 文件中添加依赖：

dependencies {debugImplementation 'com.squareup.leakcanary:leakcanary-android:1.5.4'releaseImplementation 'com.squareup.leakcanary:leakcanary-android-no-op:1.5.4'
}

debug 和 release 版本中使用的是不同的库。LeakCanary 运行时会经常执行 GC 操作，在 release 版本中会影响效率。android-no-op 版本中基本没有逻辑实现，用于 release 版本。

然后实现自己的 Application 类：

public class ExampleApplication extends Application {@Override public void onCreate() {super.onCreate();if (LeakCanary.isInAnalyzerProcess(this)) {// This process is dedicated to LeakCanary for heap analysis.// You should not init your app in this process.return;}LeakCanary.install(this);// Normal app init code...}
}

这样就集成完成了。当 LeakCanary 检测到内存泄露时，会自动弹出 Notification 通知开发者发生内存泄漏的 Activity 和引用链，以便进行修复。

源码分析

从入口函数 LeakCanary.install(this) 开始分析：

LeakCanary.install

LeakCanary.java

/*** Creates a {@link RefWatcher} that works out of the box, and starts watching activity* references (on ICS+).*/
public static RefWatcher install(Application application) {return refWatcher(application).listenerServiceClass(DisplayLeakService.class).excludedRefs(AndroidExcludedRefs.createAppDefaults().build()).buildAndInstall();
}

LeakCanary.refWatcher
LeakCanary.java

/** Builder to create a customized {@link RefWatcher} with appropriate Android defaults. */
public static AndroidRefWatcherBuilder refWatcher(Context context) {return new AndroidRefWatcherBuilder(context);
}

refWatcher() 方法新建了一个 AndroidRefWatcherBuilder 对象，该对象继承于 RefWatcherBuilder 类，配置了一些默认参数，利用建造者构建一个 RefWatcher 对象。

AndroidRefWatcherBuilder.listenerServiceClass
AndroidRefWatcherBuilder.java

public AndroidRefWatcherBuilder listenerServiceClass(Class<? extends AbstractAnalysisResultService> listenerServiceClass) {return heapDumpListener(new ServiceHeapDumpListener(context, listenerServiceClass));
}

RefWatcherBuilder.java

/** @see HeapDump.Listener */
public final T heapDumpListener(HeapDump.Listener heapDumpListener) {this.heapDumpListener = heapDumpListener;return self();
}

DisplayLeakService.java

/*** Logs leak analysis results, and then shows a notification which will start {@link* DisplayLeakActivity}.** You can extend this class and override {@link #afterDefaultHandling(HeapDump, AnalysisResult,* String)} to add custom behavior, e.g. uploading the heap dump.*/
public class DisplayLeakService extends AbstractAnalysisResultService {}

listenerServiceClass() 方法绑定了一个后台服务 DisplayLeakService，这个服务主要用来分析内存泄漏结果并发送通知。你可以继承并重写这个类来进行一些自定义操作，比如上传分析结果等。

RefWatcherBuilder.excludedRefs
RefWatcherBuilder.java

public final T excludedRefs(ExcludedRefs excludedRefs) {this.excludedRefs = excludedRefs;return self();
}

AndroidExcludedRefs.java

/*** This returns the references in the leak path that can be ignored for app developers. This* doesn't mean there is no memory leak, to the contrary. However, some leaks are caused by bugs* in AOSP or manufacturer forks of AOSP. In such cases, there is very little we can do as app* developers except by resorting to serious hacks, so we remove the noise caused by those leaks.*/
public static ExcludedRefs.Builder createAppDefaults() {return createBuilder(EnumSet.allOf(AndroidExcludedRefs.class));
}public static ExcludedRefs.Builder createBuilder(EnumSet<AndroidExcludedRefs> refs) {ExcludedRefs.Builder excluded = ExcludedRefs.builder();for (AndroidExcludedRefs ref : refs) {if (ref.applies) {ref.add(excluded);((ExcludedRefs.BuilderWithParams) excluded).named(ref.name());}}return excluded;
}

excludedRefs() 方法定义了一些对于开发者可以忽略的路径，意思就是即使这里发生了内存泄漏，LeakCanary 也不会弹出通知。这大多是系统 Bug 导致的，无需用户进行处理。

AndroidRefWatcherBuilder.buildAndInstall

最后调用 buildAndInstall() 方法构建 RefWatcher 实例并开始监听 Activity 的引用：

AndroidRefWatcherBuilder.java

/*** Creates a {@link RefWatcher} instance and starts watching activity references (on ICS+).*/
public RefWatcher buildAndInstall() {RefWatcher refWatcher = build();if (refWatcher != DISABLED) {LeakCanary.enableDisplayLeakActivity(context);ActivityRefWatcher.install((Application) context, refWatcher);}return refWatcher;
}

看一下主要的 build() 和 install() 方法：

RefWatcherBuilder.build

RefWatcherBuilder.java

/** Creates a {@link RefWatcher}. */public final RefWatcher build() {if (isDisabled()) {return RefWatcher.DISABLED;}ExcludedRefs excludedRefs = this.excludedRefs;if (excludedRefs == null) {excludedRefs = defaultExcludedRefs();}HeapDump.Listener heapDumpListener = this.heapDumpListener;if (heapDumpListener == null) {heapDumpListener = defaultHeapDumpListener();}DebuggerControl debuggerControl = this.debuggerControl;if (debuggerControl == null) {debuggerControl = defaultDebuggerControl();}HeapDumper heapDumper = this.heapDumper;if (heapDumper == null) {heapDumper = defaultHeapDumper();}WatchExecutor watchExecutor = this.watchExecutor;if (watchExecutor == null) {watchExecutor = defaultWatchExecutor();}GcTrigger gcTrigger = this.gcTrigger;if (gcTrigger == null) {gcTrigger = defaultGcTrigger();}return new RefWatcher(watchExecutor, debuggerControl, gcTrigger, heapDumper, heapDumpListener,excludedRefs);}

build() 方法利用建造者模式构建 RefWatcher 实例，看一下其中的主要参数：

• watchExecutor : 线程控制器，在 onDestroy() 之后并且主线程空闲时执行内存泄漏检测

• debuggerControl : 判断是否处于调试模式，调试模式中不会进行内存泄漏检测

• gcTrigger : 用于 GC，watchExecutor 首次检测到可能的内存泄漏，会主动进行 GC，GC 之后会再检测一次，仍然泄漏的判定为内存泄漏，进行后续操作

• heapDumper : dump 内存泄漏处的 heap 信息，写入 hprof 文件

• heapDumpListener : 解析完 hprof 文件并通知 DisplayLeakService 弹出提醒

• excludedRefs : 排除可以忽略的泄漏路径

LeakCanary.enableDisplayLeakActivity

接下来就是最核心的 install() 方法，这里就开始观察 Activity 的引用了。在这之前还执行了一步操作，LeakCanary.enableDisplayLeakActivity(context); ：

public static void enableDisplayLeakActivity(Context context) {setEnabled(context, DisplayLeakActivity.class, true);
}

最后执行到 LeakCanaryInternals#setEnabledBlocking ：

public static void setEnabledBlocking(Context appContext, Class<?> componentClass,boolean enabled) {ComponentName component = new ComponentName(appContext, componentClass);PackageManager packageManager = appContext.getPackageManager();int newState = enabled ? COMPONENT_ENABLED_STATE_ENABLED : COMPONENT_ENABLED_STATE_DISABLED;// Blocks on IPC.packageManager.setComponentEnabledSetting(component, newState, DONT_KILL_APP);
}

这里启用了 DisplayLeakActivity 并且显示应用图标。注意，这是指的不是你自己的应用图标，是一个单独的 LeakCanary 的应用，用于展示内存泄露历史的，入口函数是 DisplayLeakActivity，在 AndroidManifest.xml 中可以看到默认情况下 android:enabled="false" :

<activityandroid:theme="@style/leak_canary_LeakCanary.Base"android:name=".internal.DisplayLeakActivity"android:process=":leakcanary"android:enabled="false"android:label="@string/leak_canary_display_activity_label"android:icon="@mipmap/leak_canary_icon"android:taskAffinity="com.squareup.leakcanary.${applicationId}"><intent-filter><action android:name="android.intent.action.MAIN"/><category android:name="android.intent.category.LAUNCHER"/></intent-filter>
</activity>

ActivityRefWatcher.install

ActivityRefWatcher.java

public static void install(Application application, RefWatcher refWatcher) {new ActivityRefWatcher(application, refWatcher).watchActivities();
}public void watchActivities() {// Make sure you don't get installed twice.stopWatchingActivities();application.registerActivityLifecycleCallbacks(lifecycleCallbacks);
}

watchActivities() 方法中先解绑生命周期回调注册 lifecycleCallbacks，再重新绑定，避免重复绑定。lifecycleCallbacks 监听了 Activity 的各个生命周期，在 onDestroy() 中开始检测当前 Activity 的引用。

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

下面着重分析 RefWatcher 是如何检测 Activity 的。

RefWatcher.watch

调用 RefWatcher#watch 检测 Activity。
RefWatcher.java

/*** Identical to {@link #watch(Object, String)} with an empty string reference name.** @see #watch(Object, String)*/
public void watch(Object watchedReference) {watch(watchedReference, "");
}/*** Watches the provided references and checks if it can be GCed. This method is non blocking,* the check is done on the {@link WatchExecutor} this {@link RefWatcher} has been constructed* with.** @param referenceName An logical identifier for the watched object.*/
public void watch(Object watchedReference, String referenceName) {if (this == DISABLED) {return;}checkNotNull(watchedReference, "watchedReference");checkNotNull(referenceName, "referenceName");final long watchStartNanoTime = System.nanoTime();String key = UUID.randomUUID().toString();retainedKeys.add(key);final KeyedWeakReference reference =new KeyedWeakReference(watchedReference, key, referenceName, queue);ensureGoneAsync(watchStartNanoTime, reference);
}

watch() 方法的参数是 Object ，LeakCanary 并不仅仅是针对 Android 的，它可以检测任何对象的内存泄漏，原理都是一致的。

这里出现了几个新面孔，先来了解一下各自是什么：

• retainedKeys : 一个 Set<String> 集合，每个检测的对象都对应着一个唯一的 key，存储在 retainedKeys 中

• KeyedWeakReference :  自定义的弱引用，持有检测对象和对用的 key 值

final class KeyedWeakReference extends WeakReference<Object> {public final String key;public final String name;KeyedWeakReference(Object referent, String key, String name,ReferenceQueue<Object> referenceQueue) {super(checkNotNull(referent, "referent"), checkNotNull(referenceQueue, "referenceQueue"));this.key = checkNotNull(key, "key");this.name = checkNotNull(name, "name");}
}

• queue : ReferenceQueue 对象，和 KeyedWeakReference 配合使用

这里有个小知识点，弱引用和引用队列 ReferenceQueue 联合使用时，如果弱引用持有的对象被垃圾回收，Java 虚拟机就会把这个弱引用加入到与之关联的引用队列中。即 KeyedWeakReference 持有的 Activity 对象如果被垃圾回收，该对象就会加入到引用队列 queue 中。

接着看看具体的内存泄漏判断过程：

RefWatcher.ensureGoneAsync

private void ensureGoneAsync(final long watchStartNanoTime, final KeyedWeakReference reference) {watchExecutor.execute(new Retryable() {@Override public Retryable.Result run() {return ensureGone(reference, watchStartNanoTime);}});
}

通过 watchExecutor 执行检测操作，这里的 watchExecutor 是 AndroidWatchExecutor 对象。

@Override protected WatchExecutor defaultWatchExecutor() {return new AndroidWatchExecutor(DEFAULT_WATCH_DELAY_MILLIS);
}

DEFAULT_WATCH_DELAY_MILLIS 为 5 s。

public AndroidWatchExecutor(long initialDelayMillis) {mainHandler = new Handler(Looper.getMainLooper());HandlerThread handlerThread = new HandlerThread(LEAK_CANARY_THREAD_NAME);handlerThread.start();backgroundHandler = new Handler(handlerThread.getLooper());this.initialDelayMillis = initialDelayMillis;maxBackoffFactor = Long.MAX_VALUE / initialDelayMillis;
}

看看其中用到的几个对象：

• mainHandler : 主线程消息队列

• handlerThread : 后台线程，HandlerThread 对象，线程名为 LeakCanary-Heap-Dump

• backgroundHandler : 上面的后台线程的消息队列

• initialDelayMillis : 5 s，即之前的 DEFAULT_WATCH_DELAY_MILLIS

@Override public void execute(Retryable retryable) {if (Looper.getMainLooper().getThread() == Thread.currentThread()) {waitForIdle(retryable, 0);} else {postWaitForIdle(retryable, 0);}
}void postWaitForIdle(final Retryable retryable, final int failedAttempts) {mainHandler.post(new Runnable() {@Override public void run() {waitForIdle(retryable, failedAttempts);}});
}void waitForIdle(final Retryable retryable, final int failedAttempts) {// This needs to be called from the main thread.Looper.myQueue().addIdleHandler(new MessageQueue.IdleHandler() {@Override public boolean queueIdle() {postToBackgroundWithDelay(retryable, failedAttempts);return false;}});
}

在具体的 execute() 过程中，不管是 waitForIdle 还是 postWaitForIdle，最终还是要切换到主线程中执行。要注意的是，这里的 IdleHandler 到底是什么时候去执行？

我们都知道 Handler 是循环处理 MessageQueue 中的消息的，当消息队列中没有更多消息需要处理的时候，且声明了 IdleHandler 接口，这是就会去处理这里的操作。即指定一些操作，当线程空闲的时候来处理。当主线程空闲时，就会通知后台线程延时 5 秒执行内存泄漏检测工作。

void postToBackgroundWithDelay(final Retryable retryable, final int failedAttempts) {long exponentialBackoffFactor = (long) Math.min(Math.pow(2, failedAttempts), maxBackoffFactor);long delayMillis = initialDelayMillis * exponentialBackoffFactor;backgroundHandler.postDelayed(new Runnable() {@Override public void run() {Retryable.Result result = retryable.run();if (result == RETRY) {postWaitForIdle(retryable, failedAttempts + 1);}}}, delayMillis);
}

下面是真正的检测过程，AndroidWatchExecutor 在执行时调用 ensureGone() 方法：

RefWatcher.ensureGone

Retryable.Result ensureGone(final KeyedWeakReference reference, final long watchStartNanoTime) {long gcStartNanoTime = System.nanoTime();long watchDurationMs = NANOSECONDS.toMillis(gcStartNanoTime - watchStartNanoTime);removeWeaklyReachableReferences();if (debuggerControl.isDebuggerAttached()) {// The debugger can create false leaks.return RETRY;}if (gone(reference)) {return DONE;}gcTrigger.runGc();removeWeaklyReachableReferences();if (!gone(reference)) {long startDumpHeap = System.nanoTime();long gcDurationMs = NANOSECONDS.toMillis(startDumpHeap - gcStartNanoTime);File heapDumpFile = heapDumper.dumpHeap();if (heapDumpFile == RETRY_LATER) {// Could not dump the heap.return RETRY;}long heapDumpDurationMs = NANOSECONDS.toMillis(System.nanoTime() - startDumpHeap);heapdumpListener.analyze(new HeapDump(heapDumpFile, reference.key, reference.name, excludedRefs, watchDurationMs,gcDurationMs, heapDumpDurationMs));}return DONE;
}

再重复一次几个变量的含义，retainedKeys 是一个 Set集合，存储检测对象对应的唯一 key 值，queue是一个引用队列，存储被垃圾回收的对象。

主要过程有一下几步：

RefWatcher.emoveWeaklyReachableReferences()

private void removeWeaklyReachableReferences() {// WeakReferences are enqueued as soon as the object to which they point to becomes weakly// reachable. This is before finalization or garbage collection has actually happened.KeyedWeakReference ref;while ((ref = (KeyedWeakReference) queue.poll()) != null) {retainedKeys.remove(ref.key);}
}

遍历引用队列 queue，判断队列中是否存在当前 Activity 的弱引用，存在则删除 retainedKeys 中对应的引用的 key值。

RefWatcher.gone()

private boolean gone(KeyedWeakReference reference) {return !retainedKeys.contains(reference.key);
}

判断 retainedKeys 中是否包含当前 Activity 引用的 key 值。

如果不包含，说明上一步操作中 retainedKeys 移除了该引用的 key 值，也就说上一步操作之前引用队列 queue 中包含该引用，GC 处理了该引用，未发生内存泄漏，返回 DONE，不再往下执行。

如果包含，并不会立即判定发生内存泄漏，可能存在某个对象已经不可达，但是尚未进入引用队列 queue。这时会主动执行一次 GC 操作之后再次进行判断。

gcTrigger.runGc()

/*** Called when a watched reference is expected to be weakly reachable, but hasn't been enqueued* in the reference queue yet. This gives the application a hook to run the GC before the {@link* RefWatcher} checks the reference queue again, to avoid taking a heap dump if possible.*/
public interface GcTrigger {GcTrigger DEFAULT = new GcTrigger() {@Override public void runGc() {// Code taken from AOSP FinalizationTest:// https://android.googlesource.com/platform/libcore/+/master/support/src/test/java/libcore/// java/lang/ref/FinalizationTester.java// System.gc() does not garbage collect every time. Runtime.gc() is// more likely to perfom a gc.Runtime.getRuntime().gc();enqueueReferences();System.runFinalization();}private void enqueueReferences() {// Hack. We don't have a programmatic way to wait for the reference queue daemon to move// references to the appropriate queues.try {Thread.sleep(100);} catch (InterruptedException e) {throw new AssertionError();}}};void runGc();
}

注意这里调用 GC 的写法，并不是使用 System.gc。System.gc 仅仅只是通知系统在合适的时间进行一次垃圾回收操作，实际上并不能保证一定执行。

主动进行 GC 之后会再次进行判定，过程同上。首先调用 removeWeaklyReachableReferences() 清除 retainedKeys 中弱引用的 key 值，再判断是否移除。如果仍然没有移除，判定为内存泄漏。

内存泄露结果处理

AndroidHeapDumper.dumpHeap

判定内存泄漏之后，调用 heapDumper.dumpHeap() 进行处理：

AndroidHeapDumper.java

@SuppressWarnings("ReferenceEquality") // Explicitly checking for named null.
@Override public File dumpHeap() {File heapDumpFile = leakDirectoryProvider.newHeapDumpFile();if (heapDumpFile == RETRY_LATER) {return RETRY_LATER;}FutureResult<Toast> waitingForToast = new FutureResult<>();showToast(waitingForToast);if (!waitingForToast.wait(5, SECONDS)) {CanaryLog.d("Did not dump heap, too much time waiting for Toast.");return RETRY_LATER;}Toast toast = waitingForToast.get();try {Debug.dumpHprofData(heapDumpFile.getAbsolutePath());cancelToast(toast);return heapDumpFile;} catch (Exception e) {CanaryLog.d(e, "Could not dump heap");// Abort heap dumpreturn RETRY_LATER;}
}

leakDirectoryProvider.newHeapDumpFile() 新建了 hprof 文件，然后调用 Debug.dumpHprofData() 方法 dump 当前堆内存并写入刚才创建的文件。

回到 RefWatcher.ensureGone() 方法中，生成 heapDumpFile 文件之后，通过 heapdumpListener 分析。

ServiceHeapDumpListener.analyze

heapdumpListener.analyze(new HeapDump(heapDumpFile, reference.key, reference.name, excludedRefs, watchDurationMs,gcDurationMs, heapDumpDurationMs));

这里的 heapdumpListener 是 ServiceHeapDumpListener 对象，接着进入 ServiceHeapDumpListener.runAnalysis() 方法。

@Override public void analyze(HeapDump heapDump) {checkNotNull(heapDump, "heapDump");HeapAnalyzerService.runAnalysis(context, heapDump, listenerServiceClass);
}

这里的 listenerServiceClass 指的是 DisplayLeakService.class，文章开头提到的 AndroidRefWatcherBuilder 中进行了配置。

@Override protected HeapDump.Listener defaultHeapDumpListener() {return new ServiceHeapDumpListener(context, DisplayLeakService.class);
}

HeapAnalyzerService.runAnalysis
HeapAnalyzerService.runAnalysis() 方法中启动了它自己，传递了两个参数，DisplayLeakService 类名和要分析的 heapDump。启动自己后，在 onHandleIntent 中进行处理。

/*** This service runs in a separate process to avoid slowing down the app process or making it run* out of memory.*/
public final class HeapAnalyzerService extends IntentService {private static final String LISTENER_CLASS_EXTRA = "listener_class_extra";private static final String HEAPDUMP_EXTRA = "heapdump_extra";public static void runAnalysis(Context context, HeapDump heapDump,Class<? extends AbstractAnalysisResultService> listenerServiceClass) {Intent intent = new Intent(context, HeapAnalyzerService.class);intent.putExtra(LISTENER_CLASS_EXTRA, listenerServiceClass.getName());intent.putExtra(HEAPDUMP_EXTRA, heapDump);context.startService(intent);}public HeapAnalyzerService() {super(HeapAnalyzerService.class.getSimpleName());}@Override protected void onHandleIntent(Intent intent) {if (intent == null) {CanaryLog.d("HeapAnalyzerService received a null intent, ignoring.");return;}String listenerClassName = intent.getStringExtra(LISTENER_CLASS_EXTRA);HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAPDUMP_EXTRA);HeapAnalyzer heapAnalyzer = new HeapAnalyzer(heapDump.excludedRefs);AnalysisResult result = heapAnalyzer.checkForLeak(heapDump.heapDumpFile, heapDump.referenceKey);AbstractAnalysisResultService.sendResultToListener(this, listenerClassName, heapDump, result);}
}

heapAnalyzer.checkForLeak

checkForLeak 方法中主要使用了 Square 公司的另一个库 haha 来分析 Android heap dump，得到结果后回调给 DisplayLeakService。

AbstractAnalysisResultService.sendResultToListener

public static void sendResultToListener(Context context, String listenerServiceClassName,HeapDump heapDump, AnalysisResult result) {Class<?> listenerServiceClass;try {listenerServiceClass = Class.forName(listenerServiceClassName);} catch (ClassNotFoundException e) {throw new RuntimeException(e);}Intent intent = new Intent(context, listenerServiceClass);intent.putExtra(HEAP_DUMP_EXTRA, heapDump);intent.putExtra(RESULT_EXTRA, result);context.startService(intent);
}

同样在 onHandleIntent 中进行处理。

DisplayLeakService.onHandleIntent

@Override protected final void onHandleIntent(Intent intent) {HeapDump heapDump = (HeapDump) intent.getSerializableExtra(HEAP_DUMP_EXTRA);AnalysisResult result = (AnalysisResult) intent.getSerializableExtra(RESULT_EXTRA);try {onHeapAnalyzed(heapDump, result);} finally {//noinspection ResultOfMethodCallIgnoredheapDump.heapDumpFile.delete();}
}

DisplayLeakService.onHeapAnalyzed

调用 onHeapAnalyzed() 之后，会将 hprof 文件删除。

DisplayLeakService.java

@Override protected final void onHeapAnalyzed(HeapDump heapDump, AnalysisResult result) {String leakInfo = leakInfo(this, heapDump, result, true);CanaryLog.d("%s", leakInfo);boolean resultSaved = false;boolean shouldSaveResult = result.leakFound || result.failure != null;if (shouldSaveResult) {heapDump = renameHeapdump(heapDump);resultSaved = saveResult(heapDump, result);}PendingIntent pendingIntent;String contentTitle;String contentText;if (!shouldSaveResult) {contentTitle = getString(R.string.leak_canary_no_leak_title);contentText = getString(R.string.leak_canary_no_leak_text);pendingIntent = null;} else if (resultSaved) {pendingIntent = DisplayLeakActivity.createPendingIntent(this, heapDump.referenceKey);if (result.failure == null) {String size = formatShortFileSize(this, result.retainedHeapSize);String className = classSimpleName(result.className);if (result.excludedLeak) {contentTitle = getString(R.string.leak_canary_leak_excluded, className, size);} else {contentTitle = getString(R.string.leak_canary_class_has_leaked, className, size);}} else {contentTitle = getString(R.string.leak_canary_analysis_failed);}contentText = getString(R.string.leak_canary_notification_message);} else {contentTitle = getString(R.string.leak_canary_could_not_save_title);contentText = getString(R.string.leak_canary_could_not_save_text);pendingIntent = null;}// New notification id every second.int notificationId = (int) (SystemClock.uptimeMillis() / 1000);showNotification(this, contentTitle, contentText, pendingIntent, notificationId);afterDefaultHandling(heapDump, result, leakInfo);
}

根据分析结果，调用 showNotification() 方法构建了一个 Notification 向开发者通知内存泄漏。

public static void showNotification(Context context, CharSequence contentTitle,CharSequence contentText, PendingIntent pendingIntent, int notificationId) {NotificationManager notificationManager =(NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);Notification notification;Notification.Builder builder = new Notification.Builder(context) //.setSmallIcon(R.drawable.leak_canary_notification).setWhen(System.currentTimeMillis()).setContentTitle(contentTitle).setContentText(contentText).setAutoCancel(true).setContentIntent(pendingIntent);if (SDK_INT >= O) {String channelName = context.getString(R.string.leak_canary_notification_channel);setupNotificationChannel(channelName, notificationManager, builder);}if (SDK_INT < JELLY_BEAN) {notification = builder.getNotification();} else {notification = builder.build();}notificationManager.notify(notificationId, notification);
}

DisplayLeakService.afterDefaultHandling

最后还会执行一个空实现的方法 afterDefaultHandling：

/*** You can override this method and do a blocking call to a server to upload the leak trace and* the heap dump. Don't forget to check {@link AnalysisResult#leakFound} and {@link* AnalysisResult#excludedLeak} first.*/
protected void afterDefaultHandling(HeapDump heapDump, AnalysisResult result, String leakInfo) {
}

你可以重写这个方法进行一些自定义的操作，比如向服务器上传泄漏的堆栈信息等。

这样，LeakCanary 就完成了整个内存泄漏检测的过程。可以看到，LeakCanary 的设计思路十分巧妙，同时也很清晰，有很多有意思的知识点，像对于弱引用和 ReferenceQueue 的使用， IdleHandler 的使用，四大组件的开启和关闭等等，都很值的大家去深究。

原创投稿：孙路遥

原文链接：https://www.jianshu.com/p/751f99918711