public class RadarView extends View { private final String TAG = "RadarView"; private static final int MSG_WHAT = 1; private static final int DELAY_TIME = 20; //設置默認寬高，雷達一般都是圓形，所以我們下面取寬高會取Math.min(寬,高) private final int DEFAULT_WIDTH = 200; private final int DEFAULT_HEIGHT = 200; //雷達的半徑 private int mRadarRadius; //雷達畫筆 private Paint mRadarPaint; //雷達底色畫筆 private Paint mRadarBg; //雷達圓圈的個數，默認4個 private int mCircleNum = 4; //雷達線條的顏色，默認為白色 private int mCircleColor = Color.WHITE; //雷達圓圈背景色 private int mRadarBgColor = Color.BLACK; //paintShader private Shader mRadarShader; //雷達掃描時候的起始和終止顏色 private int mStartColor = 0x0000ff00; private int mEndColor = 0xaa00ff00; private Matrix mMatrix; //旋轉的角度 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);   //延時DELAY_TIME后再發送消息   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);  //設置抗鋸齒  mRadarBg = new Paint(Paint.ANTI_ALIAS_FLAG);  //畫筆顏色  mRadarBg.setColor(mRadarBgColor);  //畫實心圓  mRadarBg.setStyle(Paint.Style.FILL);  //設置抗鋸齒  mRadarPaint = new Paint(Paint.ANTI_ALIAS_FLAG);  //畫筆顏色  mRadarPaint.setColor(mCircleColor);  //設置空心的畫筆，只畫圓邊  mRadarPaint.setStyle(Paint.Style.STROKE);  //畫筆寬度  mRadarPaint.setStrokeWidth(2);  //使用梯度漸變渲染器，  mRadarShader = new SweepGradient(0, 0, mStartColor, mEndColor);  mMatrix = new Matrix(); } //初始化，拓展可設置參數供布局使用 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);  //雷達的半徑為寬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);  //獲取寬度  int width = measureSize(1, DEFAULT_WIDTH, widthMeasureSpec);  //獲取高度  int height = measureSize(0, DEFAULT_HEIGHT, heightMeasureSpec);  //取最大的 寬|高  int measureSize = Math.max(width, height);  setMeasuredDimension(measureSize, measureSize); } /**  * 測繪measure  *  * @param specType 1為寬， 其他為高  * @param contentSize 默認值  */ private int measureSize(int specType, int contentSize, int measureSpec) {  int result;  //獲取測量的模式和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) {    // 根據傳入方式計算寬    result += (getPaddingLeft() + getPaddingRight());   } else {    // 根據傳入方式計算高    result += (getPaddingTop() + getPaddingBottom());   }  }  return result; } @Override protected void onDraw(Canvas canvas) {  super.onDraw(canvas);  Log.d(TAG, "onDraw " + mRotate);  mRadarBg.setShader(null);  //將畫布移動到屏幕的中心點  canvas.translate(mRadarRadius, mRadarRadius);  //繪制底色，讓雷達的線看起來更清晰  canvas.drawCircle(0, 0, mRadarRadius, mRadarBg);  //畫圓圈  for (int i = 1; i <= mCircleNum; i++) {   canvas.drawCircle(0, 0, (float) (i * 1.0 / mCircleNum * mRadarRadius), mRadarPaint);  }  //繪制雷達基線 x軸  canvas.drawLine(-mRadarRadius, 0, mRadarRadius, 0, mRadarPaint);  //繪制雷達基線 y軸  canvas.drawLine(0, mRadarRadius, 0, -mRadarRadius, mRadarPaint);  //設置顏色漸變從透明到不透明  mRadarBg.setShader(mRadarShader);  //設置矩陣  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); }}

<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="開始" /> <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>