如何制作出类似雷达扫描的效果，具体方法如下

一、效果图

二、实现思路

1、自定义控件RadarView用来画雷达的效果图，可以自定义属性包括

backgroundColor：背景颜色
circleNum：圆的数量
startColor：开始颜色
endColor：结束颜色
lineColor：线的颜色

2、通过Handler循环发送消息到MessageQueue中，将mRotate加3，使Matrix旋转mRotate，重绘雷达扫描的圆。

3、通过梯度渐变扫描渲染器SweepGradient,在绘制圆的过程中，将颜色从startColor变为endColor。

三、实例代码

public class RadarView extends View { private final String TAG = "RadarView"; private static final int MSG_WHAT = 1; private static final int DELAY_TIME = 20; //设置默认宽高，雷达一般都是圆形，所以我们下面取宽高会取Math.min(宽,高) private final int DEFAULT_WIDTH = 200; private final int DEFAULT_HEIGHT = 200; //雷达的半径 private int mRadarRadius; //雷达画笔 private Paint mRadarPaint; //雷达底色画笔 private Paint mRadarBg; //雷达圆圈的个数，默认4个 private int mCircleNum = 4; //雷达线条的颜色，默认为白色 private int mCircleColor = Color.WHITE; //雷达圆圈背景色 private int mRadarBgColor = Color.BLACK; //paintShader private Shader mRadarShader; //雷达扫描时候的起始和终止颜色 private int mStartColor = 0x0000ff00; private int mEndColor = 0xaa00ff00; private Matrix mMatrix; //旋转的角度 private int mRotate = 0; private Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { super.handleMessage(msg); mRotate += 3; postInvalidate(); mMatrix.reset(); mMatrix.preRotate(mRotate, 0, 0); //延时DELAY_TIME后再发送消息 mHandler.sendEmptyMessageDelayed(MSG_WHAT, DELAY_TIME); } }; public RadarView(Context context) { this(context, null); } public RadarView(Context context, AttributeSet attrs) { this(context, attrs, 0); } public RadarView(Context context, AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); init(context, attrs); //设置抗锯齿 mRadarBg = new Paint(Paint.ANTI_ALIAS_FLAG); //画笔颜色 mRadarBg.setColor(mRadarBgColor); //画实心圆 mRadarBg.setStyle(Paint.Style.FILL); //设置抗锯齿 mRadarPaint = new Paint(Paint.ANTI_ALIAS_FLAG); //画笔颜色 mRadarPaint.setColor(mCircleColor); //设置空心的画笔，只画圆边 mRadarPaint.setStyle(Paint.Style.STROKE); //画笔宽度 mRadarPaint.setStrokeWidth(2); //使用梯度渐变渲染器， mRadarShader = new SweepGradient(0, 0, mStartColor, mEndColor); mMatrix = new Matrix(); } //初始化，拓展可设置参数供布局使用 private void init(Context context, AttributeSet attrs) { if (attrs != null) { TypedArray ta = context.obtainStyledAttributes(attrs, R.styleable.RadarView); mStartColor = ta.getColor(R.styleable.RadarView_startColor, mStartColor); mEndColor = ta.getColor(R.styleable.RadarView_endColor, mEndColor); mRadarBgColor = ta.getColor(R.styleable.RadarView_backgroundColor, mRadarBgColor); mCircleColor = ta.getColor(R.styleable.RadarView_lineColor, mCircleColor); mCircleNum = ta.getInteger(R.styleable.RadarView_circleNum, mCircleNum); ta.recycle(); } } @Override protected void onSizeChanged(int w, int h, int oldw, int oldh) { super.onSizeChanged(w, h, oldw, oldh); //雷达的半径为宽的一半或高的一半的最小值 mRadarRadius = Math.min(w / 2, h / 2); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); //获取宽度 int width = measureSize(1, DEFAULT_WIDTH, widthMeasureSpec); //获取高度 int height = measureSize(0, DEFAULT_HEIGHT, heightMeasureSpec); //取最大的 宽|高 int measureSize = Math.max(width, height); setMeasuredDimension(measureSize, measureSize); } /** * 测绘measure * * @param specType 1为宽， 其他为高 * @param contentSize 默认值 */ private int measureSize(int specType, int contentSize, int measureSpec) { int result; //获取测量的模式和Size int specMode = MeasureSpec.getMode(measureSpec); int specSize = MeasureSpec.getSize(measureSpec); if (specMode == MeasureSpec.EXACTLY) { result = Math.max(contentSize, specSize); } else { result = contentSize; if (specType == 1) { // 根据传入方式计算宽 result += (getPaddingLeft() + getPaddingRight()); } else { // 根据传入方式计算高 result += (getPaddingTop() + getPaddingBottom()); } } return result; } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Log.d(TAG, "onDraw " + mRotate); mRadarBg.setShader(null); //将画布移动到屏幕的中心点 canvas.translate(mRadarRadius, mRadarRadius); //绘制底色，让雷达的线看起来更清晰 canvas.drawCircle(0, 0, mRadarRadius, mRadarBg); //画圆圈 for (int i = 1; i <= mCircleNum; i++) { canvas.drawCircle(0, 0, (float) (i * 1.0 / mCircleNum * mRadarRadius), mRadarPaint); } //绘制雷达基线 x轴 canvas.drawLine(-mRadarRadius, 0, mRadarRadius, 0, mRadarPaint); //绘制雷达基线 y轴 canvas.drawLine(0, mRadarRadius, 0, -mRadarRadius, mRadarPaint); //设置颜色渐变从透明到不透明 mRadarBg.setShader(mRadarShader); //设置矩阵 canvas.concat(mMatrix); canvas.drawCircle(0, 0, mRadarRadius, mRadarBg); } public void startScan() { mHandler.removeMessages(MSG_WHAT); mHandler.sendEmptyMessage(MSG_WHAT); } public void stopScan() { mHandler.removeMessages(MSG_WHAT); }}

布局文件：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:id="@+id/activity_main" android:layout_width="match_parent" android:layout_height="match_parent" > <com.android.demo.ui.shader.RadarView android:id="@+id/radarview" android:layout_width="300dp" android:layout_height="300dp" android:layout_centerInParent="true" app:backgroundColor="#000000" app:circleNum="4" app:endColor="#aaff0000" app:lineColor="#00ff00" app:startColor="#aa0000ff"/> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentLeft="true" android:layout_alignParentBottom="true" android:onClick="start" android:text="开始" /> <Button android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_alignParentRight="true" android:layout_alignParentBottom="true" android:onClick="stop" android:text="停止" /></RelativeLayout>

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