上一篇文章总结了一些常见的内存泄露场景及优化方案，这篇文章继续总结内存泄露的一些常用的检测和分析方法。
Lint代码检查
AndroidStudio自动Lint代码检查工具，一些常见的代码警告Lint工具都会给我们提示。使用也比较简单：
Analyze —> Inspect Code 然后选择检查范围：
Lint使用-1
Lint使用-2
Lint使用-3
比如如果存在非静态内部类的Handler，可能会导致内存泄露，检查结果就会显示在AndroidStudio的控制台。
其实，只要我们在设置里面勾选了Lint代码检查（AnroidStudio默认是勾选了的），在写代码的时候就会自动提示可能发生内存泄露。
Lint检查代码内存泄露
Lint提示内存泄露
通常在写Handler、静态字段、标记对象等可能存在的内存泄露时，Lint检查工具都会有一个警告提示信息，我们可以根据Lint检查的提示信息来避免这些有可能发生的内存泄露。
Android Monitor
在AndroidStudio中，可以通过Monitors来监控Memory、CPU、Network、GPU等。在Monitors监控中，我们可以获取内存的各种信息来分析内存泄露。
首先运行工程后，打开控制台的Android Monitor：
Android Monitor
在运行设备中使用app（各个页面的跳转，使用相应的各种功能），就可以看到内存使用的不断变化：
内存使用变化
淡蓝色和浅灰色区域就是内存分配的变化过程，浅灰色表示空闲内存，淡蓝色表示使用内存。
通常，我们在打开一个新的页面后，使用的内存就会增加，相应的，关闭一个页面后，系统执行了GC，使用的内存应该下降。如果我们在退出界面并执行GC后，内存使用并未下降明显，或者使用内存没有下降初始的使用大小，那么有可能就发生了内存泄露。
运行工程，在设备上操作app，观察Monitor中内存的变化，点击 initiate GC 触发GC，然后点击Dump Java Heap转出堆信息，稍等片刻，生成hprof文件，生成后会在Studio中自动打开。
hprof文件
点击右侧的Analyzer Tasks，再点击Perform Analyzer，展开下面分析结果
中的 Leaked Activities 就可以看到发生内存泄露的Activity了。
Monitor内存泄露分析
可以根据左侧的引用树，来查找持有Activity引用的位置，从而判断出哪个地方导致了内存泄露。
Mat
使用第三方的Mat工具来分析内存泄露，需要在官网下载独立版的Mat。
将Android Monitor生成的hprof文件导出为标准的hprof文件（必须这样导出，直接copy出来会报错的）：
导出hprof文件
使用Mat打开导出的hprof文件：
Mat打开hprof文件
点击Histogram（直方图），可以看到类对应的实例数量的统计。
直方图
在Class Name下面输入需要匹配的类名，根据类来查看它的实例的引用，进而分析是否存在内存泄露。
类的实例
可以看到TestActivity和MyHandler都只有一个实例被引用。
TestActivity点击右键—>Merge Shortest Paths to GC Roots —>exclude all phantom/weak/soft etc.references。
Merge Shortest Paths to GC Roots 可以查看一个对象到RC Roots是否存在引用链相连接， 在JAVA中是通过可达性（Reachability Analysis)来判断对象是否存活，这个算法的基本思想是通过一系列的称谓"GC Roots"的对象作为起始点，从这些节点开始向下搜索，搜索所走得路径称为引用链，当一个对象到GC Roots没有任何引用链相连则该对象被判定为可以被回收的对象，反之不能被回收，我们可以选择 exclude all phantom/weak/soft etc.references(排查虚引用/弱引用/软引用等）因为被虚引用/弱引用/软引用的对象可以直接被GC给回收。
参考自Android 性能优化之使用MAT分析内存泄露问题。
TestActivity实例 RC Roots引用链
可以看到TestActivity实例存在GC Roots链，TextActivity实例被mMessageQueue.mMessae.target.this$0持有，那么发生了内存泄露，我们可以根据引用链来在代码中找到内存泄露的位置。
LeakCanary
LeakCanary是square开源的检测内存泄露的第三方库。它最大的有点就是开发者只需要添加简单代码，app在运行时如果发生了内存泄露，就会很直观的将内存泄露的详细信息展示在通知栏上，这样避免了Android Monitor或者Mat等工具的繁琐的分析过程。
项目地址：https://github.com/square/leakcanary
在Gradle文件中添加依赖：
dependencies {
debugCompile 'com.squareup.leakcanary:leakcanary-android:1.5'
releaseCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'
testCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.5'
}
在入口的Application中进行初始化：
public class App extends Application {
// 模拟内存泄露场景
public static ArrayList sActivities = new ArrayList<>();
@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...
}
}
在Application中新建一个静态List，里面存储Activity，来模拟内存泄露案例：
public class TestActivity extends AppCompatActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test);
App.sActivities.add(this);
}
public void back(View view) {
finish();
}
}
运行app后，在控制台可以看到LeakCanary的日志：
04-25 10:20:46.793 D/LeakCanary: In com.xiao.memoryleakexample:1.0:1.
04-25 10:20:46.793 D/LeakCanary: * com.xiao.memoryleakexample.TestActivity has leaked:
04-25 10:20:46.793 D/LeakCanary: * GC ROOT static com.xiao.memoryleakexample.app.App.sActivities
04-25 10:20:46.793 D/LeakCanary: * references java.util.ArrayList.array
04-25 10:20:46.793 D/LeakCanary: * references array java.lang.Object[].[0]
04-25 10:20:46.793 D/LeakCanary: * leaks com.xiao.memoryleakexample.TestActivity instance
04-25 10:20:46.793 D/LeakCanary: * Retaining: 88 KB.
04-25 10:20:46.793 D/LeakCanary: * Reference Key: 915bf11a-db9f-468e-8064-d6fb103710e9
04-25 10:20:46.793 D/LeakCanary: * Device: OPPO OPPO OPPO R9 Plusm A R9PlusmA
04-25 10:20:46.793 D/LeakCanary: * Android Version: 5.1.1 API: 22 LeakCanary: 1.5 00f37f5
04-25 10:20:46.793 D/LeakCanary: * Durations: watch=5049ms, gc=207ms, heap dump=979ms, analysis=122889ms
04-25 10:20:46.793 D/LeakCanary: * Details:
04-25 10:20:46.793 D/LeakCanary: * Class com.xiao.memoryleakexample.app.App
04-25 10:20:46.793 D/LeakCanary: | static $staticOverhead = byte[24]@314667009 (0x12c17001)
04-25 10:20:46.793 D/LeakCanary: | static sActivities = java.util.ArrayList@315492800 (0x12ce09c0)
04-25 10:20:46.793 D/LeakCanary: | static serialVersionUID = -920324649544707127
04-25 10:20:46.793 D/LeakCanary: | static $change = null
04-25 10:20:46.793 D/LeakCanary: * Instance of java.util.ArrayList
04-25 10:20:46.793 D/LeakCanary: | static $staticOverhead = byte[16]@1893824473 (0x70e177d9)
04-25 10:20:46.793 D/LeakCanary: | static MIN_CAPACITY_INCREMENT = 12
04-25 10:20:46.793 D/LeakCanary: | static serialVersionUID = 8683452581122892189
04-25 10:20:46.793 D/LeakCanary: | array = java.lang.Object[12]@318048768 (0x12f50a00)
04-25 10:20:46.793 D/LeakCanary: | size = 1
04-25 10:20:46.793 D/LeakCanary: | modCount = 1
04-25 10:20:46.793 D/LeakCanary: * Array of java.lang.Object[]
04-25 10:20:46.793 D/LeakCanary: | [0] = com.xiao.memoryleakexample.TestActivity@316091520 (0x12d72c80)
04-25 10:20:46.793 D/LeakCanary: | [1] = null
04-25 10:20:46.793 D/LeakCanary: | [2] = null
04-25 10:20:46.793 D/LeakCanary: | [3] = null
04-25 10:20:46.793 D/LeakCanary: | [4] = null
04-25 10:20:46.793 D/LeakCanary: | [5] = null
04-25 10:20:46.793 D/LeakCanary: | [6] = null
04-25 10:20:46.793 D/LeakCanary: | [7] = null
04-25 10:20:46.793 D/LeakCanary: | [8] = null
04-25 10:20:46.793 D/LeakCanary: | [9] = null
04-25 10:20:46.793 D/LeakCanary: | [10] = null
04-25 10:20:46.793 D/LeakCanary: | [11] = null
04-25 10:20:46.793 D/LeakCanary: * Instance of com.xiao.memoryleakexample.TestActivity
04-25 10:20:46.793 D/LeakCanary: | static $staticOverhead = byte[16]@316125185 (0x12d7b001)
04-25 10:20:46.793 D/LeakCanary: | static serialVersionUID = 836998863274086997
04-25 10:20:46.793 D/LeakCanary: | static $change = null
04-25 10:20:46.793 D/LeakCanary: | mHandler = com.xiao.memoryleakexample.TestActivity$MyHandler@318005952 (0x12f462c0)
04-25 10:20:46.793 D/LeakCanary: | mDelegate = android.support.v7.app.AppCompatDelegateImplV14@314816320 (0x12c3b740)
04-25 10:20:46.793 D/LeakCanary: | mEatKeyUpEvent = false
04-25 10:20:46.793 D/LeakCanary: | mResources = null
04-25 10:20:46.793 D/LeakCanary: | mThemeId = 2131230884
04-25 10:20:46.793 D/LeakCanary: | mCreated = true
04-25 10:20:46.793 D/LeakCanary: | mFragments = android.support.v4.app.FragmentController@317876896 (0x12f26aa0)
04-25 10:20:46.793 D/LeakCanary: | mHandler = android.support.v4.app.FragmentActivity$1@318005920 (0x12f462a0)
04-25 10:20:46.793 D/LeakCanary: | mNextCandidateRequestIndex = 0
04-25 10:20:46.793 D/LeakCanary: | mOptionsMenuInvalidated = false
04-25 10:20:46.793 D/LeakCanary: | mPendingFragmentActivityResults = android.support.v4.util.SparseArrayCompat@318008352 (0x12f46c20)
04-25 10:20:46.793 D/LeakCanary: | mReallyStopped = true
04-25 10:20:46.793 D/LeakCanary: | mRequestedPermissionsFromFragment = false
04-25 10:20:46.793 D/LeakCanary: | mResumed = false
04-25 10:20:46.793 D/LeakCanary: | mRetaining = false
04-25 10:20:46.793 D/LeakCanary: | mStopped = true
04-25 10:20:46.793 D/LeakCanary: | mStartedActivityFromFragment = false
04-25 10:20:46.793 D/LeakCanary: | mStartedIntentSenderFromFragment = false
04-25 10:20:46.793 D/LeakCanary: | mExtraDataMap = android.support.v4.util.SimpleArrayMap@318005888 (0x12f46280)
04-25 10:20:46.793 D/LeakCanary: | mActionBar = null
04-25 10:20:46.793 D/LeakCanary: | mActivityInfo = android.content.pm.ActivityInfo@318009472 (0x12f47080)
04-25 10:20:46.793 D/LeakCanary: | mActivityTransitionState = android.app.ActivityTransitionState@317937344 (0x12f356c0)
04-25 10:20:46.793 D/LeakCanary: | mAllLoaderManagers = android.util.ArrayMap@318081312 (0x12f58920)
04-25 10:20:46.793 D/LeakCanary: | mApplication = com.xiao.memoryleakexample.app.App@315492832 (0x12ce09e0)
04-25 10:20:46.793 D/LeakCanary: | mCalled = true
04-25 10:20:46.793 D/LeakCanary: | mChangeCanvasToTranslucent = false
04-25 10:20:46.793 D/LeakCanary: | mChangingConfigurations = false
04-25 10:20:46.793 D/LeakCanary: | mCheckedForLoaderManager = true
04-25 10:20:46.793 D/LeakCanary: | mComponent = android.content.ComponentName@314990768 (0x12c660b0)
04-25 10:20:46.793 D/LeakCanary: | mConfigChangeFlags = 0
04-25 10:20:46.793 D/LeakCanary: | mContainer = android.app.Activity$1@317876848 (0x12f26a70)
04-25 10:20:46.793 D/LeakCanary: | mCurrentConfig = android.content.res.Configuration@317856672 (0x12f21ba0)
04-25 10:20:46.793 D/LeakCanary: | mDecor = null
04-25 10:20:46.793 D/LeakCanary: | mDefaultKeyMode = 0
04-25 10:20:46.793 D/LeakCanary: | mDefaultKeySsb = null
04-25 10:20:46.793 D/LeakCanary: | mDestroyed = true
04-25 10:20:46.793 D/LeakCanary: | mDoReportFullyDrawn = false
04-25 10:20:46.793 D/LeakCanary: | mEmbeddedID = null
04-25 10:20:46.793 D/LeakCanary: | mEnableDefaultActionBarUp = false
04-25 10:20:46.793 D/LeakCanary: | mEnterTransitionListener = android.app.SharedElementCallback$1@1893595344 (0x70ddf8d0)
04-25 10:20:46.793 D/LeakCanary: | mExitTransitionListener = android.app.SharedElementCallback$1@1893595344 (0x70ddf8d0)
04-25 10:20:46.793 D/LeakCanary: | mFinished = true
04-25 10:20:46.793 D/LeakCanary: | mFragments = android.app.FragmentManagerImpl@317856448 (0x12f21ac0)
04-25 10:20:46.793 D/LeakCanary: | mHandler = android.os.Handler@318005856 (0x12f46260)
04-25 10:20:46.793 D/LeakCanary: | mIdent = 578025123
04-25 10:20:46.793 D/LeakCanary: | mInstanceTracker = android.os.StrictMode$InstanceTracker@317876864 (0x12f26a80)
04-25 10:20:46.793 D/LeakCanary: | mInstrumentation = android.app.Instrumentation@315352176 (0x12cbe470)
04-25 10:20:46.793 D/LeakCanary: | mIntent = android.content.Intent@317362304 (0x12ea9080)
04-25 10:20:46.793 D/LeakCanary: | mLastNonConfigurationInstances = null
04-25 10:20:46.793 D/LeakCanary: | mLoaderManager = null
04-25 10:20:46.793 D/LeakCanary: | mLoadersStarted = false
04-25 10:20:46.793 D/LeakCanary: | mMainThread = android.app.ActivityThread@314856000 (0x12c45240)
04-25 10:20:46.803 D/LeakCanary: | mManagedCursors = java.util.ArrayList@318005792 (0x12f46220)
04-25 10:20:46.803 D/LeakCanary: | mManagedDialogs = null
04-25 10:20:46.803 D/LeakCanary: | mMenuInflater = null
04-25 10:20:46.803 D/LeakCanary: | mParent = null
04-25 10:20:46.803 D/LeakCanary: | mReferrer = java.lang.String@314984512 (0x12c64840)
04-25 10:20:46.803 D/LeakCanary: | mResultCode = 0
04-25 10:20:46.803 D/LeakCanary: | mResultData = null
04-25 10:20:46.803 D/LeakCanary: | mResumed = false
04-25 10:20:46.803 D/LeakCanary: | mSearchManager = null
04-25 10:20:46.803 D/LeakCanary: | mStartedActivity = false
04-25 10:20:46.803 D/LeakCanary: | mStopped = true
04-25 10:20:46.803 D/LeakCanary: | mTemporaryPause = false
04-25 10:20:46.803 D/LeakCanary: | mTitle = java.lang.String@316164352 (0x12d84900)
04-25 10:20:46.803 D/LeakCanary: | mTitleColor = 0
04-25 10:20:46.803 D/LeakCanary: | mTitleReady = true
04-25 10:20:46.803 D/LeakCanary: | mToken = android.os.BinderProxy@314983040 (0x12c64280)
04-25 10:20:46.803 D/LeakCanary: | mTranslucentCallback = null
04-25 10:20:46.803 D/LeakCanary: | mUiThread = java.lang.Thread@1967775656 (0x7549dfa8)
04-25 10:20:46.803 D/LeakCanary: | mVisibleBehind = false
04-25 10:20:46.803 D/LeakCanary: | mVisibleFromClient = true
04-25 10:20:46.803 D/LeakCanary: | mVisibleFromServer = true
04-25 10:20:46.803 D/LeakCanary: | mVoiceInteractor = null
04-25 10:20:46.803 D/LeakCanary: | mWindow = com.android.internal.policy.impl.PhoneWindow@315631936 (0x12d02940)
04-25 10:20:46.803 D/LeakCanary: | mWindowAdded = true
04-25 10:20:46.803 D/LeakCanary: | mWindowManager = android.view.WindowManagerImpl@318006848 (0x12f46640)
04-25 10:20:46.803 D/LeakCanary: | mInflater = com.android.internal.policy.impl.PhoneLayoutInflater@317929312 (0x12f33760)
04-25 10:20:46.803 D/LeakCanary: | mOverrideConfiguration = null
04-25 10:20:46.803 D/LeakCanary: | mResources = android.content.res.Resources@314591360 (0x12c04880)
04-25 10:20:46.803 D/LeakCanary: | mTheme = android.content.res.Resources$Theme@318006400 (0x12f46480)
04-25 10:20:46.803 D/LeakCanary: | mThemeResource = 2131230884
04-25 10:20:46.803 D/LeakCanary: | mBase = android.app.ContextImpl@317145792 (0x12e742c0)
04-25 10:20:46.803 D/LeakCanary: * Excluded Refs:
04-25 10:20:46.803 D/LeakCanary: | Field: android.view.inputmethod.InputMethodManager.mNextServedView
04-25 10:20:46.803 D/LeakCanary: | Field: android.view.inputmethod.InputMethodManager.mServedView
04-25 10:20:46.803 D/LeakCanary: | Field: android.view.inputmethod.InputMethodManager.mServedInputConnection
04-25 10:20:46.803 D/LeakCanary: | Field: android.view.inputmethod.InputMethodManager.mCurRootView
04-25 10:20:46.803 D/LeakCanary: | Field: android.animation.LayoutTransition$1.val$parent
04-25 10:20:46.803 D/LeakCanary: | Field: android.view.textservice.SpellCheckerSession$1.this$0
04-25 10:20:46.803 D/LeakCanary: | Field: android.support.v7.internal.widget.ActivityChooserModel.mActivityChoserModelPolicy
04-25 10:20:46.803 D/LeakCanary: | Field: android.widget.ActivityChooserModel.mActivityChoserModelPolicy
04-25 10:20:46.803 D/LeakCanary: | Field: android.accounts.AccountManager$AmsTask$Response.this$1
04-25 10:20:46.803 D/LeakCanary: | Field: android.media.MediaScannerConnection.mContext
04-25 10:20:46.803 D/LeakCanary: | Field: android.os.UserManager.mContext
04-25 10:20:46.803 D/LeakCanary: | Field: android.media.AudioManager$1.this$0
04-25 10:20:46.803 D/LeakCanary: | Field: android.widget.Editor$Blink.this$0
04-25 10:20:46.803 D/LeakCanary: | Field: android.net.ConnectivityManager.sInstance
04-25 10:20:46.803 D/LeakCanary: | Field: android.view.Choreographer$FrameDisplayEventReceiver.mMessageQueue (always)
04-25 10:20:46.803 D/LeakCanary: | Static field: android.text.TextLine.sCached
04-25 10:20:46.803 D/LeakCanary: | Thread:FinalizerWatchdogDaemon (always)
04-25 10:20:46.803 D/LeakCanary: | Thread:main (always)
04-25 10:20:46.803 D/LeakCanary: | Thread:LeakCanary-Heap-Dump (always)
04-25 10:20:46.803 D/LeakCanary: | Class:java.lang.ref.WeakReference (always)
04-25 10:20:46.803 D/LeakCanary: | Class:java.lang.ref.SoftReference (always)
04-25 10:20:46.803 D/LeakCanary: | Class:java.lang.ref.PhantomReference (always)
04-25 10:20:46.803 D/LeakCanary: | Class:java.lang.ref.Finalizer (always)
04-25 10:20:46.803 D/LeakCanary: | Class:java.lang.ref.FinalizerReference (always)
日志当中展示了详细的内存泄露信息。同时，在运行设备上，会以通知的形式展示内存泄露：
LeakCanary内存泄露通知
点击通知栏后会展示消息的内存泄露信息，包括泄露的具体实例、以及发生在哪个类中的具体引用位置：
LeakCanary内存泄露详细信息-1
LeakCanary内存泄露详细信息-2
最后
Lint、Android Monitor、Mat，以及LeakCanary都能让我们在平常的开发过程中非常有效的避免内存泄露，至于选择哪个工具，那种方式，就看自己平常的习惯了。个人还是更喜欢使用LeakCanary，只需要简单的集成，就可以更加快速，直观展示内存泄露的信息。