How to 2-way bind a Seekbar in custom view / component?

Question

I'm trying to use 2-way databinding on a custom view that contains a SeekBar. The layout is rather simple, but I need to reuse it across the project, hence wrapping it into a custom view/component

<androidx.constraintlayout.widget.ConstraintLayout   ... />

<TextView .../>
<TextView .../>

<SeekBar
    android:id="@+id/ds_seekbar"
    android:layout....
    android:max="9"
    android:min="0"
    android:progress="0"
   </androidx.constraintlayout.widget.ConstraintLayout>

The backing code looks like so (reduced)

CustomView @JvmOverloads constructor(
        context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0

) : ConstraintLayout(context, attrs, defStyleAttr), View.OnClickListener {

    init {
        LayoutInflater.from(context).inflate(R.layout.custom_view, this, true)
        ds_description.setOnClickListener(this)

    }

    override fun onClick(view: View) {
//onClick implementation 
        }
}

I can do the binding in the ViewModel for the layout where this custom view is going to be used, with a BindingAdapter there with custom attribute (ex. app:seekbar), but the custom view would be used multiple times and I'd prefer to have the a lot of the logic that is required into the view and have a "lighter" handling in the ViewModel.

I read Android 2-Way DataBinding With Custom View and Custom Attr and a bunch of other articles which seem to be a little different but oon the same topic, however no matter how I wrote the getter and setters I always run into the kapt exception that it cannot find the getter/setter.

Either I'm not annotating properly the methods or they have wrong signatures.

Ideally I want to have something like:

   CustomView @JvmOverloads constructor(
        context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0

) : ConstraintLayout(context, attrs, defStyleAttr), View.OnClickListener, SeekBar.OnProgressChangedListener {

... ds_seekbar.setOnProgressChangedListener(this)

And then in the main layout have the app:progress (or even better if someone can show how it's done android:progress) on the custom view for binding when passing my object.

user1927033 · Accepted Answer · 2019-03-08 12:01:51Z

Okay after more and more headscratching, here's what I've come with, that seems to work. Whether this is the proper way or how performant/reliable is - I'm not sure

@InverseBindingMethods(InverseBindingMethod(type = CustomView::class, attribute = "progress", event = "progressAttrChanged"))
CustomView @JvmOverloads constructor(...

private var progress = 0
private var mInverseBindingListener: InverseBindingListener? = null


cv_seekbar.setOnSeekBarChangeListener(object : SeekBar.OnSeekBarChangeListener {
        override fun onProgressChanged(seekBar: SeekBar, i: Int, b: Boolean) {
            progress = i + 1
            if (mInverseBindingListener != null) {
                mInverseBindingListener!!.onChange()
                cv_indicator.text = progress.toString()
            }
        }...
   })

fun getProgress(): Int {
    return progress
}

fun setProgress(p: Int) {
    if (progress != p) {
        progress = p
    }
}

fun setProgressAttrChanged(inverseBindingListener: InverseBindingListener?) {
    if (inverseBindingListener != null) {
        mInverseBindingListener = inverseBindingListener
    }
}

Then the XML is

 <com.xxx.CustomView
                android:id="@+id/xxx"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:progress="@={viewModel.dataobject.value}"
          ....
                />

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