iOS: The error "message sent to deallocated instance" occurred due to the release of CFRunLoopTimer. Let

I'm currently developing an iOS application for iOS 7, where I am running JavaScript on UiWebView multiple times. However, I often encounter a crash with the error message: '[CFRunLoopTimer release]: message sent to deallocated instance'. Occasionally, I also face errors such as 'webthread multiple thread locks not allowed'.

Despite confirming that only one thread is interacting with the UIWebView at a time, I have experimented with executing operations on various threads and queues (background, main, and global) with no success in resolving the issue.

While using Instruments in zombie mode to profile the application and reproduce the crash, I receive further insights.

Although I have meticulously checked my JavaScript code and confirmed its correctness, the error persists frequently. I have even set NSZombieEnabled = YES but to no avail.

If anyone can provide a solution or debugging tip to help resolve this issue, it would be greatly appreciated.

javascriptiosuiwebview

Answer №1

I have been dealing with a persistent bug that has plagued me for quite some time.

Despite trying various methods such as NSOperationQueue's addOperationWithBlock:, dispatch_async, and 

performSelectorOnMainThread:withObject:waitUntilDone:
, I was unable to find a solution. It felt like I was grasping at straws.

Eventually, I discovered that my issue lay in how I was calling my JavaScript code using 

[myJsContext evaluateScript:jsString];
, obtaining the JSContext from the UIWebView through 
[myWebView valueForKeyPath: @"documentView.webView.mainFrame.javaScriptContext"];
.

Instead of this, I decided to revert back to using 

[myWebView stringByEvaluatingJavaScriptFromString:jsString];
, and surprisingly, it resolved my problem (at least for now).

Perhaps this could be a potential solution for you as well if you are working with UIWebViews? My understanding is that evaluateScript: is more suitable when utilizing a JSContext without a UIWebView.

(While my answer may lack technical precision, it has proven effective for me! Feel free to explore further if you are well-versed in JavaScriptCore.)

Answer №2

After investigating, I have found a solution to this crash. Simply perform a dummy stringByEvaluatingJavaScriptFromString on the UIWebView before calling a method on the context. This issue seems to be related to the timing of the call to JavaScript on the Web Thread and how it receives replies back to the main thread. Without the creation of a timer, invoking the method results in a crash when attempting to release an uncreated timer. By utilizing the proper API stringByEvaluatingJavaScriptFromString, the necessary timer is established for use by invokeMethod.

JSContext* context = [webView valueForKeyPath:@"documentView.webView.mainFrame.javaScriptContext"];
JSValue* value = context[@"Colors"];

// Fix for timer CFRelease crash
[webView stringByEvaluatingJavaScriptFromString:nil]; 

[value invokeMethod:@"update" withArguments:@[objectID, modifier]];

Answer №3

To resolve the issue, I recommend conducting a thorough search for all instances of NSTimer within your project. Check to see if any object is unintentionally releasing it multiple times. By setting breakpoints on each method where the timer is released, you can pinpoint when this occurs.

Another helpful tip is to utilize a profiler to track all object allocations and enable NSZombie for identifying memory management problems.

Answer №4

It is crucial to remember that only the main thread should be used when calling methods on UIWebView. UIWebView is not designed to handle multiple threads, so making calls from various threads can result in unsafe behavior.

Although you may believe that only one thread is interacting with UIWebView at a given time, unfortunately, this is not sufficient. Other factors such as runloop timers and user interactions also play a role in accessing the web view. Therefore, caution must be exercised when working with UIWebView.

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