ReleasableNonNullVars

This is a delegate for those non null vars of which values will be set to null.

Use Case

Suppose you have a class called MainActivity with a nonnull property image of which type is a Bitmap. You want release that bitmap and make it available for gc when MainActivity destroyed, but image cannot be set to null.

class MainActivity: Activity {
    lateinit var image: Bitmap
    
    override fun onCreate(savedInstanceState: Bundle?){
        super.onCreate(savedInstanceState)
        image = Bitmap.create(...)
    }
    
    override fun onDestroy(){
        super.onDestroy()
        image.recycle()
        image = null // You cannot do that!!
    }
}

Otherwise if you make image nullable, the whole bunch of use cases of image will be image?.xxx with the annoying question mark.

So the ReleasableNonNull delegate comes to help.

class MainActivity: Activity {
    var image by releasableNotNull<Bitmap>()
    
    override fun onCreate(savedInstanceState: Bundle?){
        super.onCreate(savedInstanceState)
        image = Bitmap.create(...)
    }
    
    override fun onDestroy(){
        super.onDestroy()
        image.recycle()
        ::image.release() // You simply make the backing value null, thus making the gc of this Bitmap instance possible. 
    }
}

You can use ::image.isInitialized to test whether it has been initialized and ::image.release() to release the backing field.

Works like a charm.

Use in your project

It has been deployed to jCenter.

compile "com.bennyhuo.kotlin:releasable-nonnull-vars:1.1.0"

Change Log

1.1.0

• Use a WeakIdentityMap instead of the original WeakHashMap to solve the problem of improper implementation of equality.

1.0.1

• Make the kotlin-stdlib compileOnly not to conflict with the kotlin version in the user project.

Theory

If you have the kotlin-reflect.jar in your classpath, reflection will be used. Otherwise, it will use an WeakMap to help find the delegate object.

Issue

Please feel free to issue and pull request.

License

MIT License