Quick Summary
The "Activity Not Responding" (ANR) error in Android means the application's UI thread has been blocked for too long, typically more than 5 seconds. This prevents the app from responding to user input, leading the operating system to display a dialog giving the user the option to wait or force close the application.
Common Causes
- Long-Running Operations on the Main Thread: Performing network calls, complex calculations, large database queries, or any potentially lengthy tasks directly on the main (UI) thread will block it and cause the ANR error. The main thread is responsible for handling UI updates and user interactions; blocking it makes the app unresponsive.
- Deadlocks: If multiple threads are waiting for each other to release resources (locks), a deadlock can occur. This can freeze the application as neither thread can proceed, causing an ANR.
- Broadcast Receivers Taking Too Long: Broadcast receivers, especially if registered directly in the manifest, can contribute to ANRs if they perform time-consuming operations or execute on the main thread. The system gives broadcast receivers a limited amount of time to execute.
- Intensive I/O Operations: Reading from or writing to files on the device's storage (especially external storage) can be slow and block the main thread, especially if the files are large or the storage is fragmented.
- Slow UI Rendering: Complex UI layouts with many nested views or inefficient rendering code can cause the UI thread to lag, potentially leading to an ANR, especially on lower-powered devices.
Step-by-Step Fixes
Method 1: Move Long-Running Operations to Background Threads
Step 1: Identify the time-consuming tasks being performed on the main thread.
Step 2: Use AsyncTask, ExecutorService, HandlerThread, or Kotlin Coroutines to move these tasks to background threads.
Step 3: For example, use AsyncTask's doInBackground() method for non-UI tasks and onPostExecute() to update the UI. Ensure data passed between threads is thread-safe.
Method 2: Avoid Deadlocks
Step 1: Carefully review your code for potential deadlock situations involving multiple threads and locks.
Step 2: Ensure a consistent order of acquiring locks to prevent circular dependencies.
Step 3: Use timeouts when acquiring locks to avoid indefinite blocking. Consider using lock analysis tools to detect potential deadlocks.
Method 3: Optimize Broadcast Receivers
Step 1: If your broadcast receiver performs long-running tasks, offload these tasks to a background thread using a Service or IntentService.
Step 2: Avoid registering broadcast receivers in the manifest if possible. Use dynamically registered receivers (using Context.registerReceiver()) instead, and unregister them in onPause() or onDestroy().
Step 3: Keep the code within the broadcast receiver's onReceive() method as concise as possible.
Method 4: Use Asynchronous I/O
Step 1: Avoid performing synchronous I/O operations on the main thread.
Step 2: Use asynchronous methods for file reading and writing.
Step 3: Consider using libraries like Okio or NIO (Non-Blocking I/O) for more efficient and non-blocking I/O operations.
Method 5: Optimize UI Rendering
Step 1: Use the Hierarchy Viewer and Profile GPU Rendering tools in Android Studio to identify UI performance bottlenecks.
Step 2: Optimize your layouts by reducing nesting, using <merge> tags, and avoiding unnecessary overdraw.
Step 3: Use RecyclerView for displaying large lists of data efficiently, reusing view holders to minimize object creation.
Step 4: Cache bitmaps and other resources to avoid reloading them repeatedly. Consider using a library, such as Glide or Picasso, for efficient image loading and caching.