Impossible to reorder/insert new layers at runtime

[jacobtabak]

It seems that the current API of this library makes it impossible to reorder the layers (or insert new layers) to ParallaxLayerLayout at runtime.

For example, consider this XML pseudocode:

<ParallaxLayerLayout>
  <ImageView/>
  <ImageView/>
</ParallaxLayerLayout>

I want to insert another view at index 0, 1, or 2, depending on how the layers are ordered.

val layerIndex = data.layerIndex
parallaxLayerLayout.addChild(myView, layerIndex)

The newly added layer will not have any parallax effect.

This is because ParallaxLayerLayout.computeOffsets is only called once after inflate - and it is a private method. Since the view has already been inflated, the offsets are never computed for the newly added layer, and it has no parallax effect.

Workaround:
Use reflection to call ParallaxLayerLayout.computeOffsets() after adding the new view.

Proposed permanent fixes:

• ParallaxLayerLayout.LayoutParams.customIndex should be public - if this field can be modified via XML, there should be no reason not to allow it to be modified programmatically.
• Override addChild methods to automatically update the layout params of all the other children to allow seamless, automatic insertion of new layers.

[Sloy]

Hi @jacobtabak!
Your proposed fix sound reasonable.

We're not using this library in our app anymore, so we're not actively maintaining it. But if you want to open a Pull Request we'll be happy to merge it and release an update :)