InvalidEditText

Supporting custom states is very simple as it involves only adding a state attribute and overriding one method responsible for assembling a state array. You can read more about custom states here.

I prepared a custom EditText class supporting a state of being invalid. I started with a simple view extending AppCompatEditText and added a valid boolean property.

class InvalidEditText @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null
) : AppCompatEditText(context, attrs) {

    private var _valid: Boolean = false
    var valid
        get() = _valid
        set(value) {
            if (_valid == value)
                return
            _valid = value
            refreshDrawableState()
        }
}

The important thing is to call refreshDrawableState() so the view is refreshed after changing the invalid property. Then I added a custom attribute to attrs.xml:

<attr name="guide_state_invalid" format="boolean" />

The key part is to add the new attribute to the state array when the view is in an invalid state.

class InvalidEditText @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null
) : AppCompatEditText(context, attrs) {
    // ..

    override fun onCreateDrawableState(extraSpace: Int): IntArray {
        if (!valid) {
            val drawableState = super.onCreateDrawableState(extraSpace + 1)
            drawableState[drawableState.size - 1] = R.attr.guide_state_invalid
            return drawableState
        }
        return super.onCreateDrawableState(extraSpace)
    }
}

Now I can create a color selector :

<selector
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
    <item android:color="@color/carbon_red_400" app:guide_state_invalid="true" />
    <item android:color="?android:attr/textColorPrimary" />
</selector>

And use it with InvalidEditText like this:

<com.github.zieiony.guide.invalidedittext.InvalidEditText
    android:id="@+id/invalidEditText"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="at least 6 characters"
    android:textColor="@color/text_color_selector"/>