在APP的启动页经常会有一些渐变效果。

如果是从半透明渐变为不透明，用View动画AlphaAnimation就能完成。

而View动画只有渐变，旋转，平移，和缩放四种动画效果，是完成不了颜色变化的任务的。所以需要用到属性动画。

下面是三种用属性动画让启动页背景颜色渐变的方法：

界面准备

几个启动页面都用同一套布局，很简单

<LinearLayout 
    android:id="@+id/launch"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical">


    <ImageView
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:layout_gravity="center_horizontal|bottom"
        android:src="@mipmap/ic_launcher" />


    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="20dp"
        android:gravity="center"
        android:text="V5.1" />

</LinearLayout>

2.ObjectAnimator.ofObject由红变蓝

这里用到了ColorDrawable来作为背景。

通过改变ColorDrawable的颜色来达到效果。

public class Launch2Activity extends AppCompatActivity {

    private LinearLayout launch;

    private ColorDrawable background;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_launch1);

        launch = (LinearLayout) findViewById(R.id.launch);

        background = new ColorDrawable(Color.RED);

        launch.setBackground(background);

        startAnimate();
    }

    private void startAnimate() {

        ArgbEvaluator evaluator = new ArgbEvaluator();
        ObjectAnimator objectAnimator = ObjectAnimator.ofObject(this, property, evaluator, Color.BLUE);
        objectAnimator.setDuration(3000);
        objectAnimator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                super.onAnimationEnd(animation);
                skip();
            }
        });
        objectAnimator.start();

    }

    private void skip() {
        startActivity(new Intent(this, MainActivity.class));
        finish();
    }

    private  Property<Launch2Activity, Object> property = new Property<Launch2Activity, Object>(Object.class, "background") {
        @Override
        public void set(Launch2Activity object, Object value) {
            object.background.setColor((Integer) value);
        }

        @Override
        public Object get(Launch2Activity object) {
            return object.background.getColor();
        }
    };
}

3.ObjectAnimator.ofInt由红变黄

这个就是简单的属性动画了。

public class Launch3Activity extends AppCompatActivity {

    private LinearLayout launch;

    private ColorDrawable background;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_launch1);
        launch = (LinearLayout) findViewById(R.id.launch);
        startAnimate();
    }

    private void startAnimate() {

        ArgbEvaluator evaluator = new ArgbEvaluator();
        ObjectAnimator objectAnimator = ObjectAnimator.ofInt(launch, "backgroundColor", Color.RED, Color.YELLOW);
        objectAnimator.setEvaluator(new ArgbEvaluator());
        objectAnimator.setDuration(3000);
        objectAnimator.addListener(new AnimatorListenerAdapter() {
            @Override
            public void onAnimationEnd(Animator animation) {
                super.onAnimationEnd(animation);
                skip();
            }
        });
        objectAnimator.start();

    }

    private void skip() {
        startActivity(new Intent(this, MainActivity.class));
        finish();
    }
}

。。。