app/src/main/java/me/zhanghai/android/douya/ui/CrossfadeText.java

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/*
 * Copyright (c) 2016 Zhang Hai <Dreaming.in.Code.ZH@Gmail.com>
 * All Rights Reserved.
 */

package me.zhanghai.android.douya.ui;

import android.animation.Animator;
import android.animation.AnimatorListenerAdapter;
import android.animation.ObjectAnimator;
import android.animation.ValueAnimator;
import android.content.Context;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import com.transitionseverywhere.Transition;
import com.transitionseverywhere.TransitionValues;

public class CrossfadeText extends Transition {

    private static final String PROPNAME_TEXT = "android:crossfadeText:text";

    public CrossfadeText() {}

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

    @Override
    public void captureStartValues(TransitionValues transitionValues) {
        captureValues(transitionValues);
    }

    @Override
    public void captureEndValues(TransitionValues transitionValues) {
        captureValues(transitionValues);
    }

    private void captureValues(TransitionValues transitionValues) {
        if (!(transitionValues.view instanceof TextView)) {
            throw new IllegalArgumentException("Target should be a TextView instead of "
                    + transitionValues.view.getClass().getName());
        }
        TextView view = (TextView) transitionValues.view;
        transitionValues.values.put(PROPNAME_TEXT, view.getText());
    }

    @Override
    public Animator createAnimator(ViewGroup sceneRoot, TransitionValues startValues,
                                   TransitionValues endValues) {
        TextView view = (TextView) startValues.view;
        CharSequence startText = (CharSequence) startValues.values.get(PROPNAME_TEXT);
        CharSequence endText = (CharSequence) endValues.values.get(PROPNAME_TEXT);
        view.setText(startText);
        ObjectAnimator animator = ObjectAnimator.ofFloat(view, View.ALPHA, 1, 0, 1);
        AnimatorListener listener = new AnimatorListener(view, endText);
        animator.addListener(listener);
        animator.addUpdateListener(listener);