Tri-States | Indeterminate Checkbox Android

Sometimes it is required to implement checkbox with 3 states

Unchecked
Checked
Indeterminate

So here is a simple example of how to implement Tri-States or you can say Indeterminate Checkbox Android
First of all, make a custom class which is extend Checkbox

import android.content.Context
import android.util.AttributeSet
import androidx.appcompat.widget.AppCompatCheckBox
import com.android.tristatescheckbox.R

class TriStatesCheckBox : AppCompatCheckBox {
    private var state = 0

    constructor(context: Context?) : super(context) {
        init()
    }

    constructor(context: Context?, attrs: AttributeSet?) : super(
        context,
        attrs
    ) {
        init()
    }

    constructor(
        context: Context?,
        attrs: AttributeSet?,
        defStyleAttr: Int
    ) : super(context, attrs, defStyleAttr) {
        init()
    }

    private fun init() {
        state = UNCHECKED
        updateBtn()
        setOnCheckedChangeListener { buttonView, isChecked ->
            // checkbox status is changed from uncheck to checked.
            state = when (state) {
                INDETERMINATE -> CHECKED
                UNCHECKED -> INDETERMINATE
                CHECKED -> UNCHECKED
                else -> CHECKED
            }
            updateBtn()
        }
    }

    private fun updateBtn() {
        var btnDrawable = R.drawable.ic_indeterminate
        btnDrawable = when (state) {
            INDETERMINATE -> R.drawable.ic_indeterminate
            UNCHECKED -> R.drawable.ic_unchecked
            CHECKED -> R.drawable.ic_checked
            else -> R.drawable.ic_unchecked
        }
        setButtonDrawable(btnDrawable)
    }

    fun getState(): Int {
        return state
    }

    fun setState(state: Int) {
        this.state = state
        updateBtn()
    }

    companion object {
        private const val UNCHECKED = 0
        private const val INDETERMINATE = 1
        private const val CHECKED = 2
    }
}

Then after using this like below

<com.android.tristatescheckbox.view.TriStatesCheckBox
        android:id="@+id/checkbox"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

Here is the output

Click Here to get full source code with example