基于Android自定义控件实现雷达效果

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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