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Code Recipes¶

This page contains code recipes to customize LeakCanary to your needs. Read through the section titles and cook your own meal! Also don’t forget to check out the FAQ.

Bug

If you think a recipe might be missing or you’re not sure that what you’re trying to achieve is possible with the current APIs, please file an issue. Your feedback helps us make LeakCanary better for the entire community.

Watching objects with a lifecycle¶

The default configuration of LeakCanary will automatically watch Activity, Fragment, Fragment View and ViewModel instances.

In your application, you may have other objects with a lifecycle, such as services, Dagger components, etc. Use AppWatcher.objectWatcher to watch instances that should be garbage collected:

class MyService : Service {

  // ...

  override fun onDestroy() {
    super.onDestroy()
    AppWatcher.objectWatcher.watch(
      watchedObject = this,
      description = "MyService received Service#onDestroy() callback"
    )
  }
}

Configuration¶

LeakCanary has a default configuration that works well for most apps. You can also customize it to your needs. The LeakCanary configuration is held by two singleton objects (AppWatcher and LeakCanary) and can be updated at any time. Most developers configure LeakCanary in their debug Application class:

class DebugExampleApplication : ExampleApplication() {

  override fun onCreate() {
    super.onCreate()
    AppWatcher.config = AppWatcher.config.copy(watchFragmentViews = false)
  }
}

Info

Create a debug application class in your src/debug/java folder. Don’t forget to also register it in src/debug/AndroidManifest.xml.

To customize the detection of retained objects at runtime, specify the watchers you wish to install via AppWatcher.manualInstall():

val watchersToInstall = AppWatcher.appDefaultWatchers(this)
  .filter { it !is FragmentAndViewModelWatcher }
AppWatcher.manualInstall(
  application = this,
  watchersToInstall = watchersToInstall
)

To customize the heap dumping & analysis, update LeakCanary.config:

LeakCanary.config = LeakCanary.config.copy(retainedVisibleThreshold = 3)

Java

In Java, use LeakCanary.Config.Builder instead:

LeakCanary.Config config = LeakCanary.getConfig().newBuilder()
   .retainedVisibleThreshold(3)
   .build();
LeakCanary.setConfig(config);

Configure the LeakCanary UI by overriding the following resources:

mipmap/leak_canary_icon see Icon and label
string/leak_canary_display_activity_label see Icon and label
bool/leak_canary_add_dynamic_shortcut see Disabling LeakCanary
bool/leak_canary_add_launcher_icon see Disabling LeakCanary
layout/leak_canary_heap_dump_toast the layout for the toast shown when the heap is dumped

Disabling LeakCanary¶

Sometimes it’s necessary to disable LeakCanary temporarily, for example for a product demo or when running performance tests. You have different options, depending on what you’re trying to achieve:

Create a build variant that does not include the LeakCanary dependencies, see Setting up LeakCanary for different product flavors.
Disable the heap dumping & analysis: LeakCanary.config = LeakCanary.config.copy(dumpHeap = false).
Hide the leak display activity launcher icon: override R.bool.leak_canary_add_launcher_icon or call LeakCanary.showLeakDisplayActivityLauncherIcon(false)

Info

When you set LeakCanary.Config.dumpHeap to false, AppWatcher.objectWatcher will still keep track of retained objects, and LeakCanary will look for these objects when you change LeakCanary.Config.dumpHeap back to true.

LeakCanary test environment detection¶

By default, LeakCanary will look for the org.junit.Test class in your classpath and if found, will disable itself to avoid running in tests. However, some apps may ship JUnit in their debug classpaths (for example, when using OkHttp’s MockWebServer) so we offer a way to customise the class that is used to determine that the app is running in a test environment.

<resources>
  <string name="leak_canary_test_class_name">assertk.Assert</string>
</resources>

Counting retained instances in release builds¶

The com.squareup.leakcanary:leakcanary-android dependency should only be used in debug builds. It depends on com.squareup.leakcanary:leakcanary-object-watcher-android which you can use in release builds to track and count retained instances.

In your build.gradle:

dependencies {
  implementation 'com.squareup.leakcanary:leakcanary-object-watcher-android:2.14'
}

In your leak reporting code:

val retainedInstanceCount = AppWatcher.objectWatcher.retainedObjectCount

LeakCanary in release builds¶

We do not recommend including LeakCanary in release builds, as it could negatively impact the experience of your customers. To avoid accidentally including the com.squareup.leakcanary:leakcanary-android dependency in a release build, LeakCanary crashes during initialization if the APK is not debuggable. You may have a good reason to create a non debuggable build that includes LeakCanary, for example for a QA build. If necessary, the crashing check can be disabled by overriding the bool/leak_canary_allow_in_non_debuggable_build resource, e.g. by creating a file under res/values with the following contents:

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <bool name="leak_canary_allow_in_non_debuggable_build">true</bool>
</resources>

Android TV¶

LeakCanary works on Android TV devices (FireTV, Nexus player, Nvidia Shield, MiBox, etc.) without any additional setup. However, there are couple things you need to be aware of:

Android TV doesn’t have notifications. LeakCanary will display Toast messages when objects become retained and when leak analysis completes. You can also check Logcat for more details.
Due to lack of notifications, the only way to manually trigger a heap dump is to background the app.
There’s a bug on API 26+ devices that prevents the activity that displays leaks from appearing in apps list. As a workaround, LeakCanary prints an adb shell command in Logcat after heap dump analysis that launches leak list activity:
```
adb shell am start -n "com.your.package.name/leakcanary.internal.activity.LeakLauncherActivity"
```
Some Android TV devices have very little memory available per app process and this might impact LeakCanary. Running the LeakCanary analysis in a separate process might help in such cases.

Icon and label¶

The activity that displays leaks comes with a default icon and label, which you can change by providing R.mipmap.leak_canary_icon and R.string.leak_canary_display_activity_label in your app:

res/
  mipmap-hdpi/
    leak_canary_icon.png
  mipmap-mdpi/
    leak_canary_icon.png
  mipmap-xhdpi/
    leak_canary_icon.png
  mipmap-xxhdpi/
    leak_canary_icon.png
  mipmap-xxxhdpi/
    leak_canary_icon.png
   mipmap-anydpi-v26/
     leak_canary_icon.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
  <string name="leak_canary_display_activity_label">MyLeaks</string>
</resources>

Matching known library leaks¶

Set LeakCanary.Config.referenceMatchers to a list that builds on top of AndroidReferenceMatchers.appDefaults:

class DebugExampleApplication : ExampleApplication() {

  override fun onCreate() {
    super.onCreate()
    LeakCanary.config = LeakCanary.config.copy(
        referenceMatchers = AndroidReferenceMatchers.appDefaults +
            AndroidReferenceMatchers.staticFieldLeak(
                className = "com.samsing.SomeSingleton",
                fieldName = "sContext",
                description = "SomeSingleton has a static field leaking a context.",
                patternApplies = {
                  manufacturer == "Samsing" && sdkInt == 26
                }
            )
    )
  }
}

Ignoring specific activities or fragment classes¶

Sometimes a 3^rd party library provides its own activities or fragments which contain a number of bugs leading to leaks of those specific 3^rd party activities and fragments. You should push hard on that library to fix their memory leaks as it’s directly impacting your application. That being said, until those are fixed, you have two options:

Add the specific leaks as known library leaks (see Matching known library leaks). LeakCanary will run when those leaks are detected and then report them as known library leaks.
Disable LeakCanary automatic activity or fragment watching (e.g. AppWatcher.config = AppWatcher.config.copy(watchActivities = false)) and then manually pass objects to AppWatcher.objectWatcher.watch.

Identifying leaking objects and labeling objects¶

class DebugExampleApplication : ExampleApplication() {

  override fun onCreate() {
    super.onCreate()
    val addEntityIdLabel = ObjectInspector { reporter ->
      reporter.whenInstanceOf("com.example.DbEntity") { instance ->
        val databaseIdField = instance["com.example.DbEntity", "databaseId"]!!
        val databaseId = databaseIdField.value.asInt!!
        labels += "DbEntity.databaseId = $databaseId"
      }
    }

    val singletonsInspector =
      AppSingletonInspector("com.example.MySingleton", "com.example.OtherSingleton")

    val mmvmInspector = ObjectInspector { reporter ->
      reporter.whenInstanceOf("com.mmvm.SomeViewModel") { instance ->
        val destroyedField = instance["com.mmvm.SomeViewModel", "destroyed"]!!
        if (destroyedField.value.asBoolean!!) {
          leakingReasons += "SomeViewModel.destroyed is true"
        } else {
          notLeakingReasons += "SomeViewModel.destroyed is false"
        }
      }
    }

    LeakCanary.config = LeakCanary.config.copy(
        objectInspectors = AndroidObjectInspectors.appDefaults +
            listOf(addObjectIdLabel, singletonsInspector, mmvmInspector)
    )
  }
}

Running the LeakCanary analysis in a separate process¶

LeakCanary runs in your main app process. LeakCanary 2 is optimized to keep memory usage low while analysing and runs in a background thread with priority Process.THREAD_PRIORITY_BACKGROUND. If you find that LeakCanary is still using too much memory or impacting the app process performance, you can configure it to run the analysis in a separate process.

All you have to do is replace the leakcanary-android dependency with leakcanary-android-process:

dependencies {
  // debugImplementation 'com.squareup.leakcanary:leakcanary-android:${version}'
  debugImplementation 'com.squareup.leakcanary:leakcanary-android-process:${version}'
}

You can call LeakCanaryProcess.isInAnalyzerProcess to check if your Application class is being created in the LeakCanary process. This is useful when configuring libraries like Firebase that may crash when running in an unexpected process.

Setting up LeakCanary for different product flavors¶

You can setup LeakCanary to run in a specific product flavors of your app. For example, create:

android {
  flavorDimensions "default"
  productFlavors {
    prod {
      // ...
    }
    qa {
      // ...
    }
    dev {
      // ...
    }
  }
}

Then, define a custom configuration for the flavor for which you want to enable LeakCanary:

android {
  // ...
}
configurations {
    devDebugImplementation {}
}

You can now add the LeakCanary dependency for that configuration:

dependencies {
  devDebugImplementation "com.squareup.leakcanary:leakcanary-android:${version}"
}

Extracting metadata from the heap dump¶

LeakCanary.Config.metadataExtractor extracts metadata from a heap dump. The metadata is then available in HeapAnalysisSuccess.metadata. LeakCanary.Config.metadataExtractor defaults to AndroidMetadataExtractor but you can replace it to extract additional metadata from the hprof.

For example, if you want to include the app version name in your heap analysis reports, you need to first store it in memory (e.g. in a static field) and then you can retrieve it in MetadataExtractor.

class DebugExampleApplication : ExampleApplication() {

  companion object {
    @JvmStatic
    lateinit var savedVersionName: String
  }

  override fun onCreate() {
    super.onCreate()

    val packageInfo = packageManager.getPackageInfo(packageName, 0)
    savedVersionName = packageInfo.versionName

    LeakCanary.config = LeakCanary.config.copy(
        metadataExtractor = MetadataExtractor { graph ->
          val companionClass =
            graph.findClassByName("com.example.DebugExampleApplication")!!

          val versionNameField = companionClass["savedVersionName"]!!
          val versionName = versionNameField.valueAsInstance!!.readAsJavaString()!!

          val defaultMetadata = AndroidMetadataExtractor.extractMetadata(graph)

          mapOf("App Version Name" to versionName) + defaultMetadata
        })
  }
}

Using LeakCanary with obfuscated apps¶

If obfuscation is turned on then leak traces will be obfuscated. It’s possible to automatically deobfuscate leak traces by using a deobfuscation gradle plugin provided by LeakCanary.

You have to add a plugin dependency in your root build.gradle file:

buildscript {
  dependencies {
    classpath 'com.squareup.leakcanary:leakcanary-deobfuscation-gradle-plugin:${version}'
  }
}

And then you need to apply and configure the plugin in your app (or library) specific build.gradle file:

apply plugin: 'com.android.application'
apply plugin: 'com.squareup.leakcanary.deobfuscation'

leakCanary {
  // LeakCanary needs to know which variants have obfuscation turned on
  filterObfuscatedVariants { variant ->
    variant.name == "debug"
  }
}

Now you can run LeakCanary on an obfuscated app and leak traces will be automatically deobfuscated.

Important: never use this plugin on a release variant. This plugin copies obfuscation mapping file and puts it inside the .apk, so if you use it on release build then the obfuscation becomes pointless because the code can be easily deobfuscated using mapping file.

Warning: R8 (Google Proguard replacement) can now understand Kotlin language constructs but the side effect is that mapping files can get very large (a couple dozen megabytes). It means that the size of .apk containing copied mapping file will increase as well. This is another reason for not using this plugin on a release variant.

Detecting leaks in JVM applications¶

While LeakCanary was designed to work out of the box on Android, it can run on any JVM with a bit of configuration.

Add the ObjectWatcher and Shark dependencies to your build file:

dependencies {
  implementation 'com.squareup.leakcanary:leakcanary-object-watcher:2.14'
  implementation 'com.squareup.leakcanary:shark:2.14'
}

Define a HotSpotHeapDumper to dump the heap:

import com.sun.management.HotSpotDiagnosticMXBean
import java.lang.management.ManagementFactory

object HotSpotHeapDumper {
  private val mBean: HotSpotDiagnosticMXBean by lazy {
    val server = ManagementFactory.getPlatformMBeanServer()
    ManagementFactory.newPlatformMXBeanProxy(
        server,
        "com.sun.management:type=HotSpotDiagnostic",
        HotSpotDiagnosticMXBean::class.java
    )
  }

  fun dumpHeap(fileName: String) {
    mBean.dumpHeap(fileName, LIVE)
  }

  private const val LIVE = true
}

Define a JvmHeapAnalyzer to analyze the heap when objects are retained and print the result to the console:

import leakcanary.GcTrigger
import leakcanary.ObjectWatcher
import leakcanary.OnObjectRetainedListener
import java.io.File
import java.text.SimpleDateFormat
import java.util.Date
import java.util.Locale.US

class JvmHeapAnalyzer(private val objectWatcher: ObjectWatcher) :
    OnObjectRetainedListener {

  private val fileNameFormat = SimpleDateFormat(DATE_PATTERN, US)

  override fun onObjectRetained() {
    GcTrigger.Default.runGc()
    if (objectWatcher.retainedObjectCount == 0) {
      return
    }
    val fileName = fileNameFormat.format(Date())
    val hprofFile = File(fileName)

    println("Dumping the heap to ${hprofFile.absolutePath}")
    HotSpotHeapDumper.dumpHeap(hprofFile.absolutePath)

    val analyzer = HeapAnalyzer(
        OnAnalysisProgressListener { step ->
          println("Analysis in progress, working on: ${step.name}")
        })

    val heapDumpAnalysis = analyzer.analyze(
        heapDumpFile = hprofFile,
        leakingObjectFinder = KeyedWeakReferenceFinder,
        computeRetainedHeapSize = true,
        objectInspectors = ObjectInspectors.jdkDefaults
    )
    println(heapDumpAnalysis)
  }
  companion object {
    private const val DATE_PATTERN = "yyyy-MM-dd_HH-mm-ss_SSS'.hprof'"
  }
}

Create an ObjectWatcher instance and configure it to watch objects for 5 seconds before notifying a JvmHeapAnalyzer instance:

val scheduledExecutor = Executors.newSingleThreadScheduledExecutor()
val objectWatcher = ObjectWatcher(
    clock = Clock {
      System.currentTimeMillis()
    },
    checkRetainedExecutor = Executor { command ->
      scheduledExecutor.schedule(command, 5, SECONDS)
    }
)

val heapAnalyzer = JvmHeapAnalyzer(objectWatcher)
objectWatcher.addOnObjectRetainedListener(heapAnalyzer)

Pass objects that you expect to be garbage collected (e.g. closed resources) to the ObjectWatcher instance:

objectWatcher.watch(
    watchedObject = closedResource,
    description = "$closedResource is closed and should be garbage collected"
)

If you end up using LeakCanary on a JVM, the community will definitely benefit from your experience, so don’t hesitate to let us know!

PackageManager.getLaunchIntentForPackage() returns LeakLauncherActivity¶

LeakCanary adds a main activity that has a Intent#CATEGORY_LAUNCHER category. PackageManager.getLaunchIntentForPackage() looks for a main activity in the category Intent#CATEGORY_INFO, and next for a main activity in the category Intent#CATEGORY_LAUNCHER. PackageManager.getLaunchIntentForPackage() returns the first activity that matches in the merged manifest of your app. If your app relies on PackageManager.getLaunchIntentForPackage(), you have two options:

Add Intent#CATEGORY_INFO to your main activity intent filter, so that it gets picked up first. This is what the Android documentation recommends.
Disable the leakcanary launcher activity by setting the leak_canary_add_launcher_icon resource boolean to false.