Android实现水波纹外扩效果

微信曾经推出了一个查找附近好友的功能，大致功能是这样的：屏幕上有一个按钮，长按按钮的时候，会有一圈圈水波纹的动画向外扩散，松手后，动画结束。

现在简单来实现这样的一个动画功能：

思路: 主要用到了下面的蓝色的图片，定义三个ImageView，background都设置为蓝色的图片，然后定义一个包括缩放和透明度变化的动画集，然后每隔一段时间，让3个ImageView依次启动这个动画集，看起来就像蓝色的圆圈像水波纹向外扩散一样。

相关实现逻辑如下：

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ImageView
        android:id="@+id/wave1"
        android:layout_width="150dp"
        android:layout_height="150dp"
        android:layout_centerInParent="true"
        android:background="@drawable/wave"
        />

    <ImageView
        android:id="@+id/wave2"
        android:layout_width="150dp"
        android:layout_height="150dp"
        android:layout_centerInParent="true"
        android:background="@drawable/wave"/>

    <ImageView
        android:id="@+id/wave3"
        android:layout_width="150dp"
        android:layout_height="150dp"
        android:layout_centerInParent="true"
        android:background="@drawable/wave" />

    <ImageView
        android:id="@+id/normal"
        android:layout_width="166dp"
        android:layout_height="166dp"
        android:layout_centerInParent="true"
        android:background="@drawable/normal" />

</RelativeLayout>

MainActivity.java

package com.jackie.waveanimation;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.MotionEvent;
import android.view.View;
import android.view.animation.AlphaAnimation;
import android.view.animation.AnimationSet;
import android.view.animation.ScaleAnimation;
import android.widget.ImageView;

public class MainActivity extends Activity {
    private ImageView mNormal, mWave1, mWave2, mWave3;

    private AnimationSet mAnimationSet1, mAnimationSet2, mAnimationSet3;

    private static final int OFFSET = 600;  //每个动画的播放时间间隔
    private static final int MSG_WAVE2_ANIMATION = 2;
    private static final int MSG_WAVE3_ANIMATION = 3;

    private Handler mHandler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case MSG_WAVE2_ANIMATION:
                    mWave2.startAnimation(mAnimationSet2);
                    break;
                case MSG_WAVE3_ANIMATION:
                    mWave3.startAnimation(mAnimationSet3);
                    break;
            }
        }
    };

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

        mNormal = (ImageView) findViewById(R.id.normal);
        mWave1 = (ImageView) findViewById(R.id.wave1);
        mWave2 = (ImageView) findViewById(R.id.wave2);
        mWave3 = (ImageView) findViewById(R.id.wave3);

        mAnimationSet1 = initAnimationSet();
        mAnimationSet2 = initAnimationSet();
        mAnimationSet3 = initAnimationSet();

        mNormal.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                switch (event.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        showWaveAnimation();
                        break;
                    case MotionEvent.ACTION_UP:
                        clearWaveAnimation();
                        break;
                    case MotionEvent.ACTION_CANCEL:
                        clearWaveAnimation();
                }
                return true;
            }
        });
    }

    private AnimationSet initAnimationSet() {
        AnimationSet as = new AnimationSet(true);
        ScaleAnimation sa = new ScaleAnimation(1f, 2.3f, 1f, 2.3f,
                ScaleAnimation.RELATIVE_TO_SELF, 0.5f,
                ScaleAnimation.RELATIVE_TO_SELF, 0.5f);
        sa.setDuration(OFFSET * 3);
        sa.setRepeatCount(Animation.INFINITE);// 设置循环
        AlphaAnimation aa = new AlphaAnimation(1, 0.1f);
        aa.setDuration(OFFSET * 3);
        aa.setRepeatCount(Animation.INFINITE);//设置循环
        as.addAnimation(sa);
        as.addAnimation(aa);
        return as;
    }

    private void showWaveAnimation() {
        mWave1.startAnimation(mAnimationSet1);
        mHandler.sendEmptyMessageDelayed(MSG_WAVE2_ANIMATION, OFFSET);
        mHandler.sendEmptyMessageDelayed(MSG_WAVE3_ANIMATION, OFFSET * 2);
    }

    private void clearWaveAnimation() {
        mWave1.clearAnimation();
        mWave2.clearAnimation();
        mWave3.clearAnimation();
    }
}

效果如下：