Android Tutorial: Use LeakCanary to detect memory leaks

Overview

The memory leak can be a headache to detect and to resolve, small memory leaks can be hidden and may be seen after a long usage of the application and hunting memory leaks is not a simple task.
In this tutorial we will create a leaked application and we will use the LeakCanary library to detect the memory leak.

Step 1: add the LeakCanary dependency to the application

Modify the app/build.gradle to add the LeakCanary dependency as follows:

	dependencies {
	debugCompile 'com.squareup.leakcanary:leakcanary-android:1.3.1'
	releaseCompile 'com.squareup.leakcanary:leakcanary-android-no-op:1.3.1'
	}

view raw build.gradle hosted with ❤ by GitHub

Step 2: Extend and configure the Application class

We need to call LeakCanary.install in onCreate method:

	package anaware.leakcanarysample;
	import android.app.Application;
	import android.content.Context;
	import com.squareup.leakcanary.LeakCanary;
	import com.squareup.leakcanary.RefWatcher;
	public class MyApplication extends Application {
	private RefWatcher refWatcher;
	public static RefWatcher getRefWatcher(Context context) {
	MyApplication application = (MyApplication) context.getApplicationContext();
	return application.refWatcher;
	}
	@Override
	public void onCreate() {
	super.onCreate();
	refWatcher = LeakCanary.install(this);
	}
	}

view raw MyApplication.java hosted with ❤ by GitHub

Step 3: Create a leaked activity

For this we will create a singleton class that saves the context:

	package anaware.leakcanarysample;
	import android.content.Context;
	public class SingletonSavesContext {
	private Context context;
	private static SingletonSavesContext instance;
	public Context getContext() {
	return context;
	}
	public void setContext(Context context) {
	this.context = context;
	}
	public static SingletonSavesContext getInstance() {
	if (instance == null) {
	instance = new SingletonSavesContext();
	}
	return instance;
	}
	}

view raw SingletonSavesContext.java hosted with ❤ by GitHub

Then, the main activity (leaked one), will use the singleton and then we'll go to a new activity:

	package anaware.leakcanarysample;
	import android.content.Context;
	import android.content.Intent;
	import android.os.AsyncTask;
	import android.support.v7.app.AppCompatActivity;
	import android.os.Bundle;
	import com.squareup.leakcanary.RefWatcher;
	public class LeakedActivity extends AppCompatActivity {
	@Override
	protected void onCreate(Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	setContentView(R.layout.activity_main);
	new MyAsyncTask().execute(this);
	}
	@Override
	public void onDestroy() {
	super.onDestroy();
	RefWatcher refWatcher = MyApplication.getRefWatcher(this);
	refWatcher.watch(this);
	}
	public class MyAsyncTask extends AsyncTask<Object, String, String> {
	private Context context;
	@Override
	protected String doInBackground(Object... params) {
	context = (Context)params[0];
	// Invoke the leak!
	SingletonSavesContext.getInstance().setContext(context);
	// Simulate long running task
	try {
	Thread.sleep(3000);
	} catch (InterruptedException e) {
	}
	return "result";
	}
	@Override
	protected void onPostExecute(String s) {
	super.onPostExecute(s);
	Intent newActivity = new Intent(context, AnotherActivity.class);
	startActivity(newActivity);
	}
	}
	}

view raw LeakedActivity.java hosted with ❤ by GitHub

Then, in the new activity we'll call System.gc to force the garbage collector in order to accelerate the analysis.

Step 4: Retrieve the analysis result

A nice notification can be shown:

The result can be retrieved from logcat:

	14211-16753/anaware.leakcanarysample D/LeakCanary: In anaware.leakcanarysample:1.0:1.
	14211-16753/anaware.leakcanarysample D/LeakCanary: * anaware.leakcanarysample.LeakedActivity has leaked:
	14211-16753/anaware.leakcanarysample D/LeakCanary: * GC ROOT static anaware.leakcanarysample.SingletonSavesContext.instance
	14211-16753/anaware.leakcanarysample D/LeakCanary: * references anaware.leakcanarysample.SingletonSavesContext.context
	14211-16753/anaware.leakcanarysample D/LeakCanary: * leaks anaware.leakcanarysample.LeakedActivity instance
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Reference Key: 226ffd5e-902c-4202-8508-2e268616e2ae
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Device: samsung samsung GT-I9305 m3xx
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Android Version: 4.4.4 API: 19 LeakCanary: 1.3.1
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Durations: watch=5007ms, gc=120ms, heap dump=617ms, analysis=13070ms
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Details:
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Class anaware.leakcanarysample.SingletonSavesContext
	14211-16753/anaware.leakcanarysample D/LeakCanary: | static $staticOverhead = byte[] [id=0x42548e79;length=24;size=40]
	14211-16753/anaware.leakcanarysample D/LeakCanary: | static instance = anaware.leakcanarysample.SingletonSavesContext [id=0x42548fb8]
	14211-16753/anaware.leakcanarysample D/LeakCanary: * Instance of anaware.leakcanarysample.SingletonSavesContext
	14211-16753/anaware.leakcanarysample D/LeakCanary: | static $staticOverhead = byte[] [id=0x42548e79;length=24;size=40]
	14211-16753/anaware.leakcanarysample D/LeakCanary: | static instance = anaware.leakcanarysample.SingletonSavesContext [id=0x42548fb8]
	14211-16753/anaware.leakcanarysample D/LeakCanary: | context = anaware.leakcanarysample.LeakedActivity [id=0x424ebbe8]

view raw LeakCanaryAnalysis.log hosted with ❤ by GitHub

Source code

Complete source code of the sample can be found in Github.
Complete documentation of LeakCanary can be found in the following links:
https://corner.squareup.com/2015/05/leak-canary.html
https://github.com/square/leakcanary