Memory Leaks in Android: Causes, Examples, and How to Fix Them

Memory leaks in Android are one of the most common reasons behind slow apps, random crashes, and OutOfMemoryError issues. As an Android developer, understanding what a memory leak is, how it happens, and how to fix it is essential if you want to ship stable, high-performance apps that users trust.

What Is a Memory Leak in Android?

A memory leak happens when your app holds references to objects that are no longer needed, preventing the garbage collector from freeing that memory. Over time, these “forgotten” objects accumulate and your app consumes more and more RAM.

When memory usage keeps growing and the system cannot reclaim enough space, the app may start lagging, triggering garbage collection frequently, and in the worst case, it can crash with an OutOfMemoryError. On low-end devices or long-running screens, even a small leak can become a serious problem.

How Android Memory Management Works (Quick Overview)

Android apps run on the ART/DEX runtime and use a garbage-collected heap. This means you do not manually free memory like in C or C++; instead, the garbage collector removes objects that are no longer reachable from any active references.

A memory leak occurs when there is still at least one strong reference pointing to an object that you are actually done with. From the garbage collector’s point of view, that object is still “in use,” so it will never be collected, even though your app will never use it again.

Why Memory Leaks Are Dangerous for Android Apps

On a desktop with lots of RAM, small leaks might not be noticeable, but on mobile devices with limited memory, leaks quickly affect user experience. Leaked Activities, Fragments, Views, or large objects like Bitmaps can easily push your app over its memory budget.

Common symptoms include slow transitions between screens, janky scrolling, long garbage collection pauses, and frequent app restarts in the background. If leaks are severe or repeated, users will simply uninstall the app and leave poor reviews.

Common Causes of Memory Leaks in Android

Memory leaks can appear in many places, but several patterns tend to cause issues again and again. Here are some of the most frequent causes you should watch out for:

1. Static References to Context, Activities, or Views

One of the biggest mistakes is storing an Activity, Fragment, or View in a static field or long-lived singleton. Because static fields live as long as the app process, they can outlive the Activity’s lifecycle.

For example:

public class MyManager {
    public static Activity currentActivity; // ❌ This can leak the Activity
}
  

If currentActivity is never cleared, the Activity object can never be garbage collected, even after the user rotates the device or navigates away.

2. Non-Static Inner Classes, Handlers, and Anonymous Classes

Non-static inner classes (including anonymous classes) hold an implicit reference to the outer class. If you create a long-running inner class instance (like a Handler or Runnable) inside an Activity, it can accidentally keep that Activity in memory.

To avoid this, use static inner classes and hold a WeakReference<Activity> when necessary, or tie the lifecycle properly to the Activity/Fragment so callbacks are removed when the screen is destroyed.

3. Long-Running Tasks, Threads, and Coroutines

Background tasks that continue running after a screen is closed can easily leak memory if they still reference the Activity. Examples include long-running threads, AsyncTask (legacy), or coroutines launched in a scope that outlives the UI.

Always cancel or complete tasks when the Activity or Fragment is destroyed, and avoid passing full Activity references to long-lived workers. Prefer lifecycle-aware components like viewModelScope or LifecycleOwner-aware observers.

4. Unregistered Listeners, Receivers, and Callbacks

Event listeners, BroadcastReceivers, observers, and callbacks that are registered but never unregistered will also cause leaks. The component that holds these listeners keeps a reference to your Activity, Fragment, or View.

For example, if you register a BroadcastReceiver in onResume(), you should unregister it in onPause(). The same applies to LiveData observers, RxJava subscriptions, and custom listener interfaces.

5. Large Objects Like Bitmaps and Collections

Bitmaps, large arrays, and heavy collections can fill the heap quickly if not released properly. Keeping references to old image caches, unneeded lists, or large data structures will prevent the garbage collector from reclaiming that memory.

Use proper caching strategies, downsample images for the current screen size, clear references when leaving a screen, and avoid static references to large objects unless you really need a global cache.

How to Detect Memory Leaks in Android

Finding memory leaks manually is difficult, but fortunately Android provides tools that make this much easier. You should integrate leak detection into your development and testing workflow.

1. Android Studio Memory Profiler

The Memory Profiler in Android Studio helps visualize your app’s memory usage over time. You can record heap dumps, inspect which objects are taking memory, and track allocations while interacting with the app.

A typical pattern for a leak: you open an Activity, close it, and then check the heap to see whether instances of that Activity are still in memory. If they remain retained after garbage collection, you almost certainly have a memory leak.

To learn more about how the Android Profiler works, we’ve already published a detailed article on this topic. Please refer to that article for an in-depth explanation.

2. LeakCanary Library

LeakCanary is a popular open-source library created by Square for automatically detecting memory leaks in Android apps. It monitors Activity, Fragment, and other object lifecycles and reports leaks during development.

Integrating LeakCanary is very simple. After adding the dependency, the library automatically watches destroyed Activities and other components. When a leak is detected, LeakCanary takes a heap dump and shows a detailed report explaining which object is leaking and through which reference chain.

// Example (Gradle - modern versions may vary)
dependencies {
    debugImplementation "com.squareup.leakcanary:leakcanary-android:<latest-version>"
}
  

Using LeakCanary early in a project can save hours of debugging later, because it surfaces leaks while you are still building features, not after users complain.

Best Practices to Prevent Memory Leaks

Although tools help you find leaks, good coding practices will prevent many of them from appearing in the first place. Here are some practical tips you can follow in every project:

• Avoid keeping strong references to Activity, Fragment, or View in static fields or long-lived singletons.
• Use Application context (getApplicationContext()) instead of Activity context when you need a long-lived context in managers or services.
• Make inner classes static where possible and use WeakReference for holding references to Activities if needed.
• Always unregister BroadcastReceivers, listeners, and callbacks in the appropriate lifecycle methods.
• Cancel coroutines, Rx subscriptions, and background tasks in onDestroy(), onStop(), or lifecycle-aware scopes.
• Release or clear large resources such as Bitmaps, adapters, and caches when the screen is no longer visible.

Interview-Style Explanation of Memory Leaks

In interviews, a common Android question is: “Explain what a memory leak is and how you would avoid it.” A strong answer usually includes both a definition and specific Android examples.

You can say something like: “A memory leak occurs when objects are kept in memory longer than needed due to active references. In Android, this often happens when Activities or Fragments are referenced by static fields, singletons, long-running tasks, or non-static inner classes. To avoid leaks, I use lifecycle-aware components, avoid static references to contexts, unregister listeners, and rely on tools like LeakCanary and the Android Studio Memory Profiler to detect issues early.”

Conclusion

Memory leaks in Android are a silent killer of app performance and stability. They occur when unused objects are kept in memory because something still holds a strong reference to them, blocking garbage collection.

By understanding the common causes—such as static references, non-static inner classes, long-running tasks, and forgotten listeners—and by using tools like Android Studio Profiler and LeakCanary, you can detect, fix, and prevent leaks before they affect real users. Following these best practices will help you build Android apps that feel smooth, responsive, and reliable on every device.