A custom View to mimic the Material behavior for the error labels

MaterialErrorTextView.java

package at.rocboron.android.widget;

import android.content.Context;
import android.util.AttributeSet;
import android.widget.TextView;

import com.nineoldandroids.animation.ObjectAnimator;
import com.nineoldandroids.animation.ValueAnimator;

/**
 * A simple widget to show an error. Its height will be 0 if nothing is shown,
 * and it will be automagically animated when someones put text on it.
 * <p/>
 * Created by Roc Boronat ([email protected]) on 30/06/2015.
 */
public class MaterialErrorTextView extends TextView implements ValueAnimator.AnimatorUpdateListener {

    //region constructors
    public MaterialErrorTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        init(attrs);
    }

    public MaterialErrorTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(attrs);
    }

    public MaterialErrorTextView(Context context) {
        super(context);
        init(null);
    }
    //endregion

    private int maxHeight;
    private CharSequence lastValue;
    private CharSequence newValue;

    @Override
    public void setText(CharSequence text, BufferType type) {
        super.setText(text, type);
        lastValue = newValue;
        newValue = text;
        startAnimationIfNeeded();
    }

    private void startAnimationIfNeeded() {
        ObjectAnimator animator = null;
        if ((lastValue == null || lastValue.equals("")) && !newValue.equals("")) {
            animator = getToMaxAnimator();
        } else if ((lastValue != null && !lastValue.equals("")) && newValue.equals("")) {
            animator = getToMinAnimator();
        }

        if (animator != null) {
            animator.addUpdateListener(this);
            animator.start();
        }
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        if (maxHeight < h) {
            maxHeight = h;
        }
    }

    private ObjectAnimator getToMaxAnimator() {
        return ObjectAnimator.ofInt(this, "height", 0, maxHeight);
    }

    private ObjectAnimator getToMinAnimator() {
        return ObjectAnimator.ofInt(this, "height", maxHeight, 0);
    }

    @Override
    public void onAnimationUpdate(ValueAnimator animation) {
        invalidate();
    }
}