android - How to avoid memory leaks due to custom static handler class?

Question

I have certain memory leaks happening in my custom handler class ,but not sure how to fix it. checkedout a couple of examples online but nothing is specific to my code so not sure how to go about it :

private val startupCallback = object: RetryCallback(NUMBER, DELAY) {
        override fun onRetry(retryCount: Int) {

            mySdkApi.applicationStartup(this)
        }

        override fun onCompleted(): Boolean {
            updateStatus(Callback.Status.StartUpSDK)

            return true
        }

        override fun onFailed(e: MyException?) {
            updateStatus(Callback.Status.StartUpSDK, "", e)
        }
    }

Android studio keeps prompting "This handler class should be static or leaks might occur".Any ideas how to go about it?

Answer 1

The Android Studio complaining is pretty reasonable. The problem is that anonymous classes capture reference to the parent class that they were created in.

There are basically two solutions the "not pretty" and the ugly.) Both of them are about WeakReference.

#1 The not pretty solution is to make a class that will take a weak ref

class ApiRetryCallback(activity: Activity): RetryCallback(NUMBER, DELAY) {

    private val weakActivity = WeakReference(activity)

    override fun onRetry(retryCount: Int) {

        weakActivity.get()!!.mySdkApi.applicationStartup(this) //or weakThis.get()? to swallow null cases
    }

    override fun onCompleted(): Boolean {
        weakActivity.get()!!.updateStatus(Callback.Status.StartUpSDK)

        return true
    }

    override fun onFailed(e: MyException?) {
        weakActivity.get()!!.updateStatus(Callback.Status.StartUpSDK, "", e)
    }
}

In activity:

private val startupCallback = ApiRetryCallback(this) //this is MainActivity here

#2 The ugly solution is based on a fact that lambdas should capture parent reference, only where there is a direct usage of it. So I came up with this substitution and I didn't see strong references in a debugger but you should check that:

private val startupCallback = {
    val weakActivity = WeakReference(this@MainActivity)

    object : RetryCallback(NUMBER, DELAY) { //returned as last expression

        override fun onRetry(retryCount: Int) {

            weakActivity.get()!!.mySdkApi.applicationStartup(this) //or weakThis.get()? to swallow null cases
        }

        //....else methods....
    }

}()

Here the lambda will be called immediately and will capture only the weak reference inside the object, also it will return the last expression wich is object.

#3 While I was writing, I came up with a third solution, which is close to #2

private val startupCallback = WeakReference(this).let { //this here is MainActivity
    val weakActivity = it //it of let scope wich is WeakReference

    object : RetryCallback(NUMBER, DELAY) { //returned as last expression

        override fun onRetry(retryCount: Int) {

            weakActivity.get()!!.mySdkApi.applicationStartup(this) //or weakThis.get()? to swallow null cases
        }

        //....else methods....
    }

}