自定义ObjectAnimator属性实现

package com.loaderman.customviewdemo;

import android.animation.ObjectAnimator;
import android.graphics.Point;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;

public class MainActivity extends AppCompatActivity {
    private FallingBallImageView ball_img;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

//

        ball_img = (FallingBallImageView) findViewById(R.id.ball_img);

        findViewById(R.id.start_anim).setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                ObjectAnimator animator = ObjectAnimator.ofObject(ball_img, "fallingPos", new FallingBallEvaluator(), new Point(0, 0), new Point(500, 500));//set函数对于的属于应该是fallingPos或者FallingPos
                animator.setDuration(2000);
                animator.start();
            }
        });
    }
}

package com.loaderman.customviewdemo;

import android.animation.TypeEvaluator;
import android.graphics.Point;

public class FallingBallEvaluator implements TypeEvaluator<Point> {
    private Point point = new Point();
    public Point evaluate(float fraction, Point startValue, Point endValue) {
        point.x = (int)(startValue.x + fraction *(endValue.x - startValue.x));

        if (fraction*2<=1){
            point.y = (int)(startValue.y + fraction*2*(endValue.y - startValue.y));
        }else {
            point.y = endValue.y;
        }
        return point;
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_gravity="center"
    tools:context="com.loaderman.customviewdemo.MainActivity">

    <com.loaderman.customviewdemo.FallingBallImageView
        android:id="@+id/ball_img"
        android:layout_width="50dp"
        android:layout_height="50dp"
        android:src="@drawable/cicle"/>

    <Button
        android:id="@+id/start_anim"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="开始动画"/>

</LinearLayout>

package com.loaderman.customviewdemo;

import android.content.Context;
import android.graphics.Point;
import android.util.AttributeSet;

public class FallingBallImageView extends android.support.v7.widget.AppCompatImageView {
    public FallingBallImageView(Context context) {
        super(context);
    }

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

    public FallingBallImageView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
    }

    public void setFallingPos(Point pos){
        layout(pos.x, pos.y, pos.x + getWidth(), pos.y + getHeight());
    }

}