Android自定义View实现雷达扫描动画

最近在项目中有用到雷达扫描动画，这个效果也常被用于扫描或定位等事件，通过一个小Demo对此进行一下总结。

动画截图如下：

Android的动画分两类：一类是Tween动画，就是对场景里的对象不断的进行图像变化来产生动画效果（旋转、平移、放缩和渐变）。另一类就是 Frame动画，即顺序的播放事先做好的图像，与gif图片原理类似。

此处的基本思想是通过自定义雷达View，不断刷新和绘制雷达View实现扫描Tween动画。

1. 首先自定义雷达View，RadarView.java代码如下：

package com.example.radar;import android.content.Context;import android.content.res.Resources;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.SweepGradient;import android.util.AttributeSet;import android.view.View;public class RadarView extends View{private Paint circlePaint;//圆形画笔private Paint linePaint;//线形画笔private Paint sweepPaint;//扫描画笔SweepGradient sweepGradient;//扇形渐变Shaderint degree = 0;public RadarView(Context context){super(context);}public RadarView(Context context, AttributeSet att){super(context,att);initPaint();}/*** @param * @return void* @Description //初始化定义的画笔  */private void initPaint(){Resources r = this.getResources();circlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);//圆形画笔，设置Paint为抗锯齿circlePaint.setARGB(255, 50, 57, 74);//设置透明度和RGB颜色circlePaint.setStrokeWidth(3);//轮廓宽度circlePaint.setStyle(Paint.Style.STROKE);linePaint = new Paint(Paint.ANTI_ALIAS_FLAG);//线性画笔linePaint.setStrokeCap(Paint.Cap.ROUND);linePaint.setARGB(150, 50, 57, 74);linePaint.setStrokeWidth(2);sweepPaint = new Paint(Paint.ANTI_ALIAS_FLAG);//雷达Shader画笔sweepPaint.setStrokeCap(Paint.Cap.ROUND);sweepPaint.setStrokeWidth(4);sweepGradient = new SweepGradient(0,0,r.getColor(R.color.start_color),r.getColor(R.color.end_color));sweepPaint.setShader(sweepGradient);}@Overrideprotected void onMeasure(int wMeasureSpec, int hMeasureSpec){int width = MeasureSpec.getSize(wMeasureSpec);int height = MeasureSpec.getSize(hMeasureSpec);int d = (width>=height)?height:width; //获取最短的边作为直径setMeasuredDimension(d,d); //重写测量方法，保证获得的画布是正方形}@Overrideprotected void onDraw(Canvas canvas){int Width = getMeasuredWidth();////计算控件的中心位置int Height = getMeasuredHeight();int pointX =  Width/2;//获得圆心坐标int pointY = Height/2;int radius = (pointX>=pointY) ? pointY : pointX;//设置半径radius -= 10;//设置半径canvas.save();//保存Canvas坐标原点degree += 5;//扫描旋转增量度数canvas.translate(pointX, pointY);//设置旋转的原点canvas.rotate(270 + degree);canvas.drawCircle(0, 0, radius, sweepPaint);//绘制扫描区域canvas.restore();//恢复原Canvas坐标(0,0)canvas.drawCircle(pointX, pointY, radius, circlePaint);//绘制3个嵌套同心圆形，使用circlePaint画笔circlePaint.setAlpha(100);//降低内部圆形的透明度circlePaint.setStrokeWidth(2);//轮廓宽度canvas.drawCircle(pointX, pointY, radius*2/3, circlePaint);canvas.drawCircle(pointX, pointY, radius/3, circlePaint);canvas.drawLine(pointX, 10, pointX, 2*radius + 10, linePaint);//绘制十字分割线 ， 竖线canvas.drawLine(10, pointY, 2*radius + 10, pointY, linePaint);canvas.save();//保存Canvas坐标原点canvas.translate(10, radius+10);//设置相对横线起始坐标float s = radius/12f;//刻度间距float minlength = s/2;//短刻度线长度float maxlength = s;//长刻度线长度for(int i=0;i<24;i++){float fromX,toX;fromX=toX=s*i;if(i%4!=0){//与圆形重叠处不画刻度if(i%2!=0){canvas.drawLine(fromX,-minlength,toX,minlength, linePaint);//绘制X轴短刻度}else{canvas.drawLine(fromX,-maxlength,toX,maxlength, linePaint);//绘制X轴长刻度}}}canvas.restore();canvas.translate(pointX, 10);//设置相对竖线起始坐标for(int i=0;i<24;i++){float fromY,toY;fromY=toY=s*i;if(i%4!=0){if(i%2!=0){canvas.drawLine(-minlength,fromY,minlength,toY, linePaint);//绘制Y短轴刻度}else{canvas.drawLine(-maxlength,fromY,maxlength,toY, linePaint);//绘制Y长轴刻度}}}}}

其中，需要用到Android渲染图像和图形的Shader类的渐变扫描子类SweepGradient，通过设置起始颜色color0和结束的color1，渲染出围绕中心点的闭合圆形渐变效果。

SweepGradient对象颜色定义如下：

<?xml version="1.0" encoding="utf-8"?><resources>    <color name="start_color">#696969</color>    <color name="end_color">#20ffffff</color></resources>

2. 实现RadarView的扫描动画

activity_main.xml简单布局文件，添加自定义RadarView和控制按钮，代码如下：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    android:background="#ADD8E6">    <com.example.radar.RadarView        android:id="@+id/radar"         android:layout_width="300dp"        android:layout_height="300dp"        android:layout_centerInParent="true"        android:visibility="invisible"/>        <Button        android:id="@+id/btn"         android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_centerHorizontal="true"        android:layout_alignParentBottom="true"        android:layout_marginBottom="10dp"        android:text="start"        android:textSize="16sp"        /></RelativeLayout>

创建RadarView的扫描刷新线程RadarSweep，当在线程radarView调用postInvalidate()方法时，会刷新RadarView的onDraw()方法，随之degree变量增加旋转角度，sweepGradient产生旋转效果。

MainActivity.java代码如下：

package com.example.radar;import android.os.Bundle;import android.app.Activity;import android.view.View;import android.view.animation.Animation;import android.view.animation.AnimationUtils;import android.widget.Button;public class MainActivity extends Activity {private RadarView radarView;private Button btn;private Thread radarSweepThread;private boolean startRadar = true;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);radarView = (RadarView) findViewById(R.id.radar);btn = (Button) findViewById(R.id.btn);btn.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {// TODO Auto-generated method stubif (startRadar) {btn.setText("end");radarView.setVisibility(View.VISIBLE);// 设置可见Animation radarAnimEnter = AnimationUtils.loadAnimation(MainActivity.this, R.anim.radar_anim_enter);// 初始化radarView进入动画radarView.startAnimation(radarAnimEnter);// 开始进入动画radarSweepThread = new Thread(new RadarSweep());// 雷达扫描线程radarSweepThread.start();startRadar = false;} else {btn.setText("start");Animation radarAnimEnter = AnimationUtils.loadAnimation(MainActivity.this, R.anim.radar_anim_exit);// 初始化radarView退出动画radarView.startAnimation(radarAnimEnter);// 开始进入动画radarView.setVisibility(View.INVISIBLE);// 设置不可见radarSweepThread.interrupt();// 停止扫描更新startRadar = true;}}});}/** * @ClassName RadarSweep * @Description 雷达扫描动画刷新线程类 */private class RadarSweep implements Runnable {int i = 1;@Overridepublic void run() {// TODO Auto-generated method stubwhile (!Thread.currentThread().isInterrupted() && i == 1) {try {radarView.postInvalidate();// 刷新radarView, 执行onDraw();Thread.sleep(10);// 暂停当前线程，更新UI线程} catch (InterruptedException e) {i = 0;// 结束当前扫描线程标志符break;}}}}}

其中，RadarView载入和淡出的动画代码如下：

\Radar\res\anim\radar_anim_enter.xml

<?xml version="1.0" encoding="utf-8"?><set xmlns:android="http://schemas.android.com/apk/res/android" >       <!-- 雷达动画由大到正常 -->       <scale        android:duration="2000"        android:fromXScale="1.5"        android:fromYScale="1.5"        android:interpolator="@android:anim/decelerate_interpolator"        android:pivotX="50%"        android:pivotY="50%"        android:toXScale="1.0"        android:toYScale="1.0" /></set>

\Radar\res\anim\radar_anim_exit.xml

<?xml version="1.0" encoding="utf-8"?><set xmlns:android="http://schemas.android.com/apk/res/android" >    <!-- 雷达动画由正常到缩小退出 -->    <scale        android:duration="1000"        android:fromXScale="1.0"        android:fromYScale="1.0"        android:interpolator="@android:anim/accelerate_interpolator"        android:pivotX="50%"        android:pivotY="50%"        android:toXScale="0.0"        android:toYScale="0.0" /></set>

简单的自定义雷达动画Demo介绍到此结束，如果想要更复杂和逼真的效果，还可以添加更多的效果和功能：如在雷达扫描的表盘上添加随机发光点，以及增加雷达刷新线程的控制参数，实现其他线程事件对雷达扫描的监听，如完成某个事件后自动退出雷达扫描动画等。时间有限，不在此一一赘述。