/**
 * 画固定的尺子
 * @param canvas
 */
 private void drawLine(Canvas canvas) {
  canvas.save();
  int height = mHeight;
  int drawCount = 0;//已经画了刻度线的个数
  float xPosition;
  for(int i=0; drawCount<=mMaxLineCount; i++){
   xPosition = (mLineDivider*mDensity + mLineWidth)*drawCount + mLeftWidth;
   if(i%5 == 0 && i != 0){//刻度为5的倍数，但同时不是10的倍数
    canvas.drawLine(xPosition,height*0.85f-mPaddingBottom,xPosition,height*0.15f+mPaddingTop,mLinePaint);
   }else if(i == 0){//刻度为10的倍数
    canvas.drawLine(xPosition,height-mPaddingBottom,xPosition,mPaddingTop,mLinePaint);
   }else {//普通的刻度
    canvas.drawLine(xPosition,height*0.75f-mPaddingBottom,xPosition,height*0.25f+mPaddingTop,mLinePaint);
   }
   drawCount++;
  }
  canvas.restore();
 }

package com.xhunmon.radiorule;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.util.SparseArray;
import android.view.MotionEvent;
import android.view.View;

/**
 * user: uidq0530 ,date: 2017-04-16.
 * description：收音机FM搜台尺子
 *
 * @author xhunmon
 */

public class RadioRulerView extends View {

 private static final String tag = "RadioRulerView";

 private int mHeight; //view的高度
 private int mWidth;  //view的宽度
 private Paint mLinePaint; //固定的尺子画笔
 private int mLineWidth;//尺子刻度线的宽
 private int mLineColor;//固定尺子刻度线的颜色
 private int mMoveLineColor;//移动尺子刻度线的颜色
 private float mDensity;
 private int mLineDivider; //两条刻度线间的距离
 private float mLeftWidth; //尺子离view左边的距离

 private int mMaxLineCount = 220; //总共要画多少条刻度
 private Paint mMoveLinePaint; //移动尺子的画笔
 private int mValue;  //尺子被选中的值
 private float mMaxX; //onTouch中能触摸的最大x值
 private float mMinX; //onTouch中能触摸的最小x值

 private OnValueChangeListener mListener;

 private SparseArray<PointF> activePointers;
 private PointF xPoint;
 private int mPaddingBottom;
 private int mPaddingTop;
 private boolean mIsAuto = false;

 public RadioRulerView(Context context) {
  this(context,null);
 }

 public RadioRulerView(Context context, AttributeSet attrs) {
  this(context, attrs,0);
 }

 public RadioRulerView(Context context, AttributeSet attrs, int defStyleAttr) {
  this(context, attrs, defStyleAttr,0);
 }

 public RadioRulerView(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) {
  super(context, attrs, defStyleAttr, defStyleRes);
  mDensity = context.getResources().getDisplayMetrics().density;
  TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.RadioRulerView, defStyleAttr, defStyleRes);
  mLineWidth = (int) a.getDimension(R.styleable.RadioRulerView_line_width,5*mDensity);
  mLineDivider = (int) a.getDimension(R.styleable.RadioRulerView_line_divider,15*mDensity);

  mLineColor = a.getColor(R.styleable.RadioRulerView_line_color,0xff888888);
  mMoveLineColor = a.getColor(R.styleable.RadioRulerView_move_line_color,0xffff0000);
  a.recycle();

  init();
 }


 private void init() {
  activePointers = new SparseArray<>();

  mLinePaint = new Paint();
  mLinePaint.setAntiAlias(true);
  mLinePaint.setColor(mLineColor);
  mLinePaint.setStrokeWidth(mLineWidth);
  mLinePaint.setStyle(Paint.Style.STROKE);

  mMoveLinePaint = new Paint();
  mMoveLinePaint.setAntiAlias(true);
  mMoveLinePaint.setColor(mMoveLineColor);
  mMoveLinePaint.setStrokeWidth(mLineWidth);
  mMoveLinePaint.setStyle(Paint.Style.STROKE);
 }

 //此方法在view的尺寸确定后调用
 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  mHeight = getHeight();
  mWidth = getWidth();
  mPaddingBottom = getPaddingBottom();
  mPaddingTop = getPaddingTop();
  mLeftWidth = (mWidth - mMaxLineCount*(mLineWidth +mLineDivider))/2;
  mMaxX = mMaxLineCount*(mLineWidth +mLineDivider) + mLeftWidth;
  mMinX = mLeftWidth;
 }

 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  drawLine(canvas);

  drawMoveLine(canvas);
 }

 /**
  * 画固定的尺子
  * @param canvas
  */
 private void drawLine(Canvas canvas) {
  canvas.save();
  int height = mHeight;
  int drawCount = 0;//已经画了刻度线的个数
  float xPosition;
  for(int i=0; drawCount<=mMaxLineCount; i++){
   xPosition = (mLineDivider*mDensity + mLineWidth)*drawCount + mLeftWidth;
   if(i%5 == 0 && i != 0){//刻度为5的倍数，但同时不是10的倍数
    canvas.drawLine(xPosition,height*0.85f-mPaddingBottom,xPosition,height*0.15f+mPaddingTop,mLinePaint);
   }else if(i == 0){//刻度为10的倍数
    canvas.drawLine(xPosition,height-mPaddingBottom,xPosition,mPaddingTop,mLinePaint);
   }else {//普通的刻度
    canvas.drawLine(xPosition,height*0.75f-mPaddingBottom,xPosition,height*0.25f+mPaddingTop,mLinePaint);
   }
   drawCount++;
  }
  canvas.restore();
 }


 /**
  * 搜索FM频道的刻度线
  * @param canvas
  */
 private void drawMoveLine(Canvas canvas) {
  canvas.save();
  xPoint = activePointers.valueAt(0);
  if (xPoint != null) {
   canvas.drawLine(xPoint.x,mHeight-mPaddingBottom, xPoint.x,mPaddingTop,mMoveLinePaint);
   setValue(eventXValue(xPoint.x));
  }else {
   canvas.drawLine(mMinX,mHeight-mPaddingBottom, mMinX,mPaddingTop,mMoveLinePaint);
  }
  canvas.restore();
 }


 @Override
 public boolean onTouchEvent(MotionEvent event) {
  int pointerIndex = event.getActionIndex();
  int pointerId = event.getPointerId(pointerIndex);
  switch (event.getActionMasked()) {
   case MotionEvent.ACTION_DOWN:
   case MotionEvent.ACTION_POINTER_DOWN: {
    float downX = event.getX(pointerIndex);
    if(downX > mMaxX || downX < mMinX) break;
    PointF position = new PointF(downX, event.getY(pointerIndex));
    activePointers.put(pointerId, position);
    break;
   }
   case MotionEvent.ACTION_MOVE: {
    int pointerCount = event.getPointerCount();
    for (int i = 0; i < pointerCount; i++) {
     PointF point = activePointers.get(event.getPointerId(i));
     if (point == null) continue;
     float moveX = event.getX(i);
     if(moveX > mMaxX || moveX < mMinX) break;
     point.x = event.getX(i);
     point.y = event.getY(i);
    }
    break;
   }
   case MotionEvent.ACTION_UP:
   case MotionEvent.ACTION_POINTER_UP:
   case MotionEvent.ACTION_CANCEL: {
    int pointerCount = event.getPointerCount();
    PointF point = activePointers.get(event.getPointerId(pointerCount-1));
    if (point == null) break;
    float upX = event.getX(pointerCount-1);
    if(upX > mMaxX || upX < mMinX) break;
    point.x = eventXValue(event.getX(pointerCount-1));
    point.y = event.getY(pointerCount-1);
    break;
   }
  }
  invalidate();

  return true;
 }

 /**
  *作用：使得放手后MoveLine和Line重合；精确mValue
  * @param x onTouch中的event.getX()
  * @return
  */
 public int eventXValue(float x){
  mLineDivider = (int) (mLineDivider*mDensity);
  return (int) ((x-mLeftWidth)%(mLineWidth +mLineDivider)>((mLineWidth +mLineDivider)/2)
      ? (((mLineWidth +mLineDivider)*((int)((x-mLeftWidth)/(mLineWidth +mLineDivider))+1))+mLeftWidth)
      : (((mLineWidth +mLineDivider)*((int)((x-mLeftWidth)/(mLineWidth +mLineDivider))))+mLeftWidth));
 }

 /**
  * 设置最大刻度线个数
  * @param count
  */
 public void setMaxLineCount(int count) {
  mMaxLineCount = count;
 }

 /**
  * 设置是否启用自动搜索功能
  * @param isAuto
  */
 public void setAutoSearchFM(boolean isAuto){
  this.mIsAuto = isAuto;
 }

 /**
  * 开始自动搜台
  */
 public void startAutoSeachFM(){
  if(mIsAuto)
   new Thread(new SeachThread()).start();
 }

 /**
  * 搜台要在开启子线程
  */
 private class SeachThread implements Runnable{

  @Override
  public void run() {
   while(mIsAuto){
    xPoint = activePointers.valueAt(0);
    if(xPoint != null){
     xPoint.x += (mLineWidth + mLineDivider);
     if(xPoint.x > mMaxX) xPoint.x = mLeftWidth;
    }else {
     PointF position = new PointF(mLeftWidth, mHeight);
     activePointers.put(0, position);
    }
    try {
     Thread.sleep(200);
    } catch (InterruptedException e) {
     e.printStackTrace();
    }
    postInvalidate();
   }
  }
 }

 /*****************************值传递的回调*************************************/
 public interface OnValueChangeListener {
  void onValueChange(float value);
 }

 public void setOnValueChangeListener(OnValueChangeListener listener){
  mListener = listener;
 }

 private void setValue(float value) {
  if(mListener != null){
   mValue = (int) ((value - mLeftWidth)/(mLineDivider*mDensity + mLineWidth));
   //FM的范围从88.0 ~ 108.0
   mListener.onValueChange(mValue/10f + 88);
  }
 }

 /******************************************************************/
}

package com.xhunmon.radiorule;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.TextView;

public class MainActivity extends Activity implements RadioRulerView.OnValueChangeListener,
  CompoundButton.OnCheckedChangeListener, View.OnClickListener {

 private TextView mShow;
 private RadioRulerView mRule;
 private CheckBox mCbAuto;
 private Button mBtStart;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  mShow = (TextView) findViewById(R.id.tv);
  mRule = (RadioRulerView) findViewById(R.id.rule);
  mCbAuto = (CheckBox) findViewById(R.id.cb_auto);
  mBtStart = (Button) findViewById(R.id.bt_start);

  mRule.setMaxLineCount(200);//FM从88.0 ~ 108.0总共有200频道
  mRule.setOnValueChangeListener(this);
  mCbAuto.setOnCheckedChangeListener(this);
  mBtStart.setOnClickListener(this);

 }

 @Override
 public void onValueChange(float value) {
  mShow.setText("FM："+value);
 }

 @Override
 public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
  if(isChecked){
   mRule.setAutoSearchFM(true);
  }else {
   mRule.setAutoSearchFM(false);
  }
 }

 @Override
 public void onClick(View v) {
  if(v.getId() == R.id.bt_start){
   mRule.startAutoSeachFM();
  }
 }
}