最近在做一个项目，其中有一个页面是要做一个类似于雷达扫描的效果。于是找了其他应用的类似的效果参考一下，刚好我使用的华为手机里的手机管家--病毒查杀页面就是一个雷达扫描的效果。而且看它的样式也挺不错的，刚好符合我的要求。所以就决定仿照它的样式自定义一个类似效果的RadarView。
这是华为手机管家的效果：
图片
我写完这个RadarView之后觉得这个View的实现虽然不难，却使用到了自定义属性、View的Measure、Paint、Canvas和坐标的计算等这些自定义View常用的知识，是一个不错的自定义View练习例子，所以决定写一篇博客把它记录起来。
由于我需要雷达的扫描效果，所以画中间的百分比数字。RadarView可以根据自己的需求配置View的主题颜色、扫描颜色、扫描速度、圆圈数量、是否显示水滴等功能样式，方便实现各种样式的情况。下面是自定义RadarView的代码。
public class RadarView extends View {
//默认的主题颜色
private int DEFAULT_COLOR = Color.parseColor("#91D7F4");
// 圆圈和交叉线的颜色
private int mCircleColor = DEFAULT_COLOR;
//圆圈的数量 不能小于1
private int mCircleNum = 3;
//扫描的颜色 RadarView会对这个颜色做渐变透明处理
private int mSweepColor = DEFAULT_COLOR;
//水滴的颜色
private int mRaindropColor = DEFAULT_COLOR;
//水滴的数量 这里表示的是水滴最多能同时出现的数量。因为水滴是随机产生的，数量是不确定的
private int mRaindropNum = 4;
//是否显示交叉线
private boolean isShowCross = true;
//是否显示水滴
private boolean isShowRaindrop = true;
//扫描的转速，表示几秒转一圈
private float mSpeed = 3.0f;
//水滴显示和消失的速度
private float mFlicker = 3.0f;
private Paint mCirclePaint;// 圆的画笔
private Paint mSweepPaint; //扫描效果的画笔
private Paint mRaindropPaint;// 水滴的画笔
private float mDegrees; //扫描时的扫描旋转角度。
private boolean isScanning = false;//是否扫描
//保存水滴数据
private ArrayList mRaindrops = new ArrayList<>();
public RadarView(Context context) {
super(context);
init();
}
public RadarView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
getAttrs(context, attrs);
init();
}
public RadarView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
getAttrs(context, attrs);
init();
}
/**
* 获取自定义属性值
*
* @param context
* @param attrs
*/
private void getAttrs(Context context, AttributeSet attrs) {
if (attrs != null) {
TypedArray mTypedArray = context.obtainStyledAttributes(attrs, R.styleable.RadarView);
mCircleColor = mTypedArray.getColor(R.styleable.RadarView_circleColor, DEFAULT_COLOR);
mCircleNum = mTypedArray.getInt(R.styleable.RadarView_circleNum, mCircleNum);
if (mCircleNum < 1) {
mCircleNum = 3;
}
mSweepColor = mTypedArray.getColor(R.styleable.RadarView_sweepColor, DEFAULT_COLOR);
mRaindropColor = mTypedArray.getColor(R.styleable.RadarView_raindropColor, DEFAULT_COLOR);
mRaindropNum = mTypedArray.getInt(R.styleable.RadarView_raindropNum, mRaindropNum);
isShowCross = mTypedArray.getBoolean(R.styleable.RadarView_showCross, true);
isShowRaindrop = mTypedArray.getBoolean(R.styleable.RadarView_showRaindrop, true);
mSpeed = mTypedArray.getFloat(R.styleable.RadarView_speed, mSpeed);
if (mSpeed <= 0) {
mSpeed = 3;
}
mFlicker = mTypedArray.getFloat(R.styleable.RadarView_flicker, mFlicker);
if (mFlicker <= 0) {
mFlicker = 3;
}
mTypedArray.recycle();
}
}
/**
* 初始化
*/
private void init() {
// 初始化画笔
mCirclePaint = new Paint();
mCirclePaint.setColor(mCircleColor);
mCirclePaint.setStrokeWidth(1);
mCirclePaint.setStyle(Paint.Style.STROKE);
mCirclePaint.setAntiAlias(true);
mRaindropPaint = new Paint();
mRaindropPaint.setStyle(Paint.Style.FILL);
mRaindropPaint.setAntiAlias(true);
mSweepPaint = new Paint();
mSweepPaint.setAntiAlias(true);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
//设置宽高,默认200dp
int defaultSize = dp2px(getContext(), 200);
setMeasuredDimension(measureWidth(widthMeasureSpec, defaultSize),
measureHeight(heightMeasureSpec, defaultSize));
}
/**
* 测量宽
*
* @param measureSpec
* @param defaultSize
* @return
*/
private int measureWidth(int measureSpec, int defaultSize) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
result = specSize;
} else {
result = defaultSize + getPaddingLeft() + getPaddingRight();
if (specMode == MeasureSpec.AT_MOST) {
result = Math.min(result, specSize);
}
}
result = Math.max(result, getSuggestedMinimumWidth());
return result;
}
/**
* 测量高
*
* @param measureSpec
* @param defaultSize
* @return
*/
private int measureHeight(int measureSpec, int defaultSize) {
int result = 0;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
if (specMode == MeasureSpec.EXACTLY) {
result = specSize;
} else {
result = defaultSize + getPaddingTop() + getPaddingBottom();
if (specMode == MeasureSpec.AT_MOST) {
result = Math.min(result, specSize);
}
}
result = Math.max(result, getSuggestedMinimumHeight());
return result;
}
@Override
protected void onDraw(Canvas canvas) {
//计算圆的半径
int width = getWidth() - getPaddingLeft() - getPaddingRight();
int height = getHeight() - getPaddingTop() - getPaddingBottom();
int radius = Math.min(width, height) / 2;
//计算圆的圆心
int cx = getPaddingLeft() + (getWidth() - getPaddingLeft() - getPaddingRight()) / 2;
int cy = getPaddingTop() + (getHeight() - getPaddingTop() - getPaddingBottom()) / 2;
drawCircle(canvas, cx, cy, radius);
if (isShowCross) {
drawCross(canvas, cx, cy, radius);
}
//正在扫描
if (isScanning) {
if (isShowRaindrop) {
drawRaindrop(canvas, cx, cy, radius);
}
drawSweep(canvas, cx, cy, radius);
//计算雷达扫描的旋转角度
mDegrees = (mDegrees + (360 / mSpeed / 60)) % 360;
//触发View重新绘制，通过不断的绘制实现View的扫描动画效果
invalidate();
}
}
/**
* 画圆
*/
private void drawCircle(Canvas canvas, int cx, int cy, int radius) {
//画mCircleNum个半径不等的圆圈。
for (int i = 0; i < mCircleNum; i++) {
canvas.drawCircle(cx, cy, radius - (radius / mCircleNum * i), mCirclePaint);
}
}
/**
* 画交叉线
*/
private void drawCross(Canvas canvas, int cx, int cy, int radius) {
//水平线
canvas.drawLine(cx - radius, cy, cx + radius, cy, mCirclePaint);
//垂直线
canvas.drawLine(cx, cy - radius, cx, cy + radius, mCirclePaint);
}
/**
* 生成水滴。水滴的生成是随机的，并不是每次调用都会生成一个水滴。
*/
private void generateRaindrop(int cx, int cy, int radius) {
// 最多只能同时存在mRaindropNum个水滴。
if (mRaindrops.size() < mRaindropNum) {
// 随机一个20以内的数字，如果这个数字刚好是0，就生成一个水滴。
// 用于控制水滴生成的概率。
boolean probability = (int) (Math.random() * 20) == 0;
if (probability) {
int x = 0;
int y = 0;
int xOffset = (int) (Math.random() * (radius - 20));
int yOffset = (int) (Math.random() * (int) Math.sqrt(1.0 * (radius - 20) * (radius - 20) - xOffset * xOffset));
if ((int) (Math.random() * 2) == 0) {
x = cx - xOffset;
} else {
x = cx + xOffset;
}
if ((int) (Math.random() * 2) == 0) {
y = cy - yOffset;
} else {
y = cy + yOffset;
}
mRaindrops.add(new Raindrop(x, y, 0, mRaindropColor));
}
}
}
/**
* 删除水滴
*/
private void removeRaindrop() {
Iterator iterator = mRaindrops.iterator();
while (iterator.hasNext()) {
Raindrop raindrop = iterator.next();
if (raindrop.radius > 20 || raindrop.alpha < 0) {
iterator.remove();
}
}
}
/**
* 画雨点(就是在扫描的过程中随机出现的点)。
*/
private void drawRaindrop(Canvas canvas, int cx, int cy, int radius) {
generateRaindrop(cx, cy, radius);
for (Raindrop raindrop : mRaindrops) {
mRaindropPaint.setColor(raindrop.changeAlpha());
canvas.drawCircle(raindrop.x, raindrop.y, raindrop.radius, mRaindropPaint);
//水滴的扩散和透明的渐变效果
raindrop.radius += 1.0f * 20 / 60 / mFlicker;
raindrop.alpha -= 1.0f * 255 / 60 / mFlicker;
}
removeRaindrop();
}
/**
* 画扫描效果
*/
private void drawSweep(Canvas canvas, int cx, int cy, int radius) {
//扇形的透明的渐变效果
SweepGradient sweepGradient = new SweepGradient(cx, cy,
new int[]{Color.TRANSPARENT, changeAlpha(mSweepColor, 0), changeAlpha(mSweepColor, 168),
changeAlpha(mSweepColor, 255), changeAlpha(mSweepColor, 255)
}, new float[]{0.0f, 0.6f, 0.99f, 0.998f, 1f});
mSweepPaint.setShader(sweepGradient);
//先旋转画布，再绘制扫描的颜色渲染，实现扫描时的旋转效果。
canvas.rotate(-90 + mDegrees, cx, cy);
canvas.drawCircle(cx, cy, radius, mSweepPaint);
}
/**
* 开始扫描
*/
public void start() {
if (!isScanning) {
isScanning = true;
invalidate();
}
}
/**
* 停止扫描
*/
public void stop() {
if (isScanning) {
isScanning = false;
mRaindrops.clear();
mDegrees = 0.0f;
}
}
/**
* 水滴数据类
*/
private static class Raindrop {
int x;
int y;
float radius;
int color;
float alpha = 255;
public Raindrop(int x, int y, float radius, int color) {
this.x = x;
this.y = y;
this.radius = radius;
this.color = color;
}
/**
* 获取改变透明度后的颜色值
*
* @return
*/
public int changeAlpha() {
return RadarView.changeAlpha(color, (int) alpha);
}
}
/**
* dp转px
*/
private static int dp2px(Context context, float dpVal) {
return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,
dpVal, context.getResources().getDisplayMetrics());
}
/**
* 改变颜色的透明度
*
* @param color
* @param alpha
* @return
*/
private static int changeAlpha(int color, int alpha) {
int red = Color.red(color);
int green = Color.green(color);
int blue = Color.blue(color);
return Color.argb(alpha, red, green, blue);
}
}
自定义属性：在res/values下创建attrs.xml
效果图：
效果图
源码下载