Android Window Leak Error: Complete Guide

The “Activity has leaked window” error in Android occurs when a window (typically a dialog) is added to an activity but not properly removed before the activity is destroyed. This creates a reference to a window that no longer has an associated activity, causing the Android system to throw a WindowLeaked exception. In your case, the error trace shows that a ProgressDialog was being displayed through an AsyncTask (PreparePairingLinkageData.onPreExecute()) at line 183 in viewP.java, but the activity finished before the dialog could be dismissed.

Contents

• Understanding the Window Leak Error
• Common Causes of Window Leaks
• How to Fix Window Leak Issues
• Best Practices for Preventing Window Leaks
• Debugging Window Leak Problems

Understanding the Window Leak Error

A window leak error occurs when Android’s WindowManager detects that a window (like a Dialog, ProgressDialog, or PopupWindow) was attached to an Activity but wasn’t properly detached before the Activity was destroyed. According to Repeato’s research, this happens when “a window was added to the activity but was not removed before the activity was destroyed”.

The error stack trace you provided clearly shows the issue:

• The dialog was being shown via Dialog.show(Dialog.java:239)
• This occurred in an AsyncTask’s onPreExecute() method
• The activity attempted to finish while the dialog was still active

This creates a memory leak where the window maintains a reference to the destroyed activity, preventing proper garbage collection and potentially causing application instability.

Common Causes of Window Leaks

Based on the research findings, several common scenarios trigger this error:

Dialogs Not Dismissed Before Activity Finishes

The most frequent cause is failing to call dismiss() on dialogs before an activity ends. As one StackOverflow answer explains: “You must need to dismiss/cancel your dialog once activity is finishing. It occurs usually if dialogs are not dismissed before Activity is ended”.

AsyncTask and Background Thread Issues

Your specific case involves an AsyncTask, which is a common culprit. The error occurs when:

• Background threads attempt to show UI elements after the activity is gone
• The activity finishes while an AsyncTask is still running
• Progress dialogs are shown in AsyncTasks but not properly handled

According to StackOverflow discussions, this happens because “Progress dialog have a context of an activity but you may doing finish activity before complete the async task”.

Configuration Changes

Screen rotations or other configuration changes can cause activity recreation while UI elements are being displayed, leading to window leaks if not handled properly.

ProgressDialog Without Dismissal

Moving to a new activity without dismissing a progress dialog is another common cause, as noted in multiple sources: “the problem is you are moving to new activity without dismissing the progress dialogue. this will cause leaked window error”.

How to Fix Window Leak Issues

Immediate Solutions for Your Case

1. Dismiss Dialogs in Lifecycle Methods
   Add dialog dismissal in appropriate lifecycle methods:

   java

   @Override
   protected void onDestroy() {
       super.onDestroy();
       if (progressDialog != null && progressDialog.isShowing()) {
           progressDialog.dismiss();
       }
   }
   

   As Repeato recommends: “Ensure you call dismiss() on any dialog before the activity exits”.

2. Handle AsyncTask Properly
   For your AsyncTask issue, implement the following:

   java

   @Override
   protected void onPreExecute() {
       if (isActivityAlive()) { // Add this check
           progressDialog = new ProgressDialog(mContext);
           progressDialog.setMessage("Working...");
           progressDialog.show();
       }
   }
   
   private boolean isActivityAlive() {
       return !isFinishing() && !isDestroyed();
   }
   

3. Cancel Dialogs in onStop()
   As suggested in the research: “use DialogFragment or cancel progress dialog when Activity get stop”.

Advanced Solutions

Use DialogFragment Instead of Regular Dialogs
DialogFragments are more lifecycle-aware and automatically handle configuration changes:

public class MyProgressDialogFragment extends DialogFragment {
    @Override
    public Dialog onCreateDialog(Bundle savedInstanceState) {
        ProgressDialog dialog = new ProgressDialog(getActivity());
        dialog.setMessage("Loading...");
        return dialog;
    }
}

Implement Proper AsyncTask Handling
According to StackOverflow answers, you should:

@Override
protected void onPostExecute(Void result) {
    if (progressDialog != null && progressDialog.isShowing()) {
        progressDialog.dismiss();
    }
}

@Override
protected void onCancelled() {
    if (progressDialog != null && progressDialog.isShowing()) {
        progressDialog.dismiss();
    }
}

Best Practices for Preventing Window Leaks

1. Always Dismiss Dialogs

• Call dismiss() in onStop(), onDestroy(), or onPause()
• Check if dialog is showing before dismissing

2. Use Context-Aware Components

• DialogFragment instead of Dialog
• Use getApplicationContext() for long-lived operations
• Avoid holding Activity references in static variables

3. Handle Configuration Changes

• Use android:configChanges in AndroidManifest.xml
• Override onRetainNonConfigurationInstance() for AsyncTasks
• Consider using ViewModel components

4. Validate Activity State

Always check if the activity is still alive before showing UI elements from background threads:

private void showDialogSafely() {
    if (isActivityAlive()) {
        // Show dialog safely
    }
}

Debugging Window Leak Problems

Analyzing the Stack Trace

Your error trace shows the problem originates from:

• Dialog.show() at line 239 in Dialog.java
• PreparePairingLinkageData.onPreExecute() at line 183 in viewP.java
• Called during AsyncTask.execute() at line 94 in viewP.java

This indicates that the dialog was being shown in the AsyncTask’s pre-execute phase, but the activity finished before the dialog could be dismissed.

Debugging Steps

1. Add Logging: Log dialog creation and dismissal
2. Check Lifecycle: Verify activity state before showing dialogs
3. Review AsyncTask: Ensure proper cancellation handling
4. Use LeakCanary: Detect memory leaks automatically

Common Patterns to Watch For

• ProgressDialog shown in AsyncTask without proper dismissal
• AlertDialog shown in background thread without activity state check
• Custom dialogs not dismissed in lifecycle methods
• Multiple dialogs created without proper reference management

The key takeaway is that window leaks occur from improper dialog management, especially in scenarios involving background operations and configuration changes. By implementing proper dialog dismissal and lifecycle-aware components, you can prevent these errors and ensure your Android application runs smoothly.

Sources

1. Stack Overflow - Activity has leaked window that was originally added
2. Repeato - Resolving the “Activity Has Leaked Window” Error
3. Stack Overflow - ProgressDialog : how to prevent Leaked Window
4. Mobikul - Activity has leaked window
5. About Android - Android Window Leak

Conclusion

The “Activity has leaked window” error is a common Android issue that occurs when dialogs or other UI elements aren’t properly dismissed before an activity is destroyed. Based on your error log and the research findings, the key points are:

1. Dialogs must be dismissed before activities finish - use dismiss() methods in lifecycle callbacks
2. AsyncTasks need proper handling - check activity state before showing UI elements and implement cancellation logic
3. Use modern Android components like DialogFragment instead of regular dialogs for better lifecycle management
4. Configuration changes can trigger leaks - handle screen rotations and other configuration changes appropriately
5. Always validate activity state before showing dialogs from background threads

By implementing these practices, you can prevent window leaks and ensure your Android application provides a smooth, error-free user experience. The most immediate fix for your case would be to add proper dialog dismissal in your AsyncTask’s lifecycle methods and activity destruction handlers.