Custom View Example With Custom Drawable Attributes/Parameters (Kotlin)

Edit /res/values/attrs.xml to specify style name, attribute name and format (use reference for drawable).

NOTE: I have yet to found the full documentation for attribute format, but some clues is available here and here.

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="PreferencesBadge">
        <attr name="badge" format="reference" />
    </declare-styleable>
</resources>

Create the custom view class, using Resources.Theme.obtainStyledAttributes to get the custom attributes.

Use TypedArray.getResourceId to get the resource number and get drawable using AppCompatResources.getDrawable.

NOTE: Resources$NotFoundException will happen if using TypedArray.getDrawable to retrieve vector image.

class BadgePreference : Preference {    private var badge: Drawable? = null    private lateinit var titleView: TextView    constructor(context: Context) : super(context)    constructor(context: Context, attrs: AttributeSet) : super(context, attrs) {        val a = context.theme.obtainStyledAttributes(                attrs,                R.styleable.PreferencesBadge,                0, 0)        try {            // Resources$NotFoundException if vector image            // badge = a.getDrawable(R.styleable.PreferencesBadge_badge)            val drawableResId = a.getResourceId(R.styleable.PreferencesBadge_badge, -1);            badge = AppCompatResources.getDrawable(context, drawableResId)        }        finally {            a.recycle()        }    }    constructor(context: Context, attrs: AttributeSet, defStyle: Int) : super(context, attrs, defStyle)    override fun onBindView(view: View) {        super.onBindView(view)        titleView = view.findViewById(android.R.id.title) as TextView        if (badge != null) {            setBadge(badge)        }    }    fun setBadge(badge: Drawable?) {        this.badge = badge        titleView.compoundDrawablePadding = 20        titleView.setCompoundDrawablesWithIntrinsicBounds(null, null, badge, null)    }}

To specify the custom attributes in XML declaration.

<PreferenceScreen
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res/com.mypackage.myapp">

    <com.mypackage.myapp.BadgePreference
        android:key="@string/pref_key_export_text"
        android:title="Export as Text"
        android:summary="Export as data as plain text file. Keep the file safe as it is not encrypted"
        custom:badge="@drawable/ic_upcoming"
        />

</PreferenceScreen>

References:

https://developer.android.com/training/custom-views/create-view.html