Android自定义收音机搜台控件RadioRulerView

前言：像这类的自定义控件有非常多的开源项目，但还是没有找到我项目想要的，所以简单实现了一个，下面简单讲讲实现原理。

效果图：

实现思路：

首先画固定背景尺子，而实现这个则要计算刻度线的宽度、刻度线间的距离，以及要确定刻度线的总是，根据这些可以求出第一条刻度线的x坐标，使得整个尺子居中；下图为尺子尺寸的计算方法：

贴上关键代码：

 
 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%10 != 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%10 == 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();
 }

然后画出可以拖动的刻度线（首图粉红色线），要实现该功能其实不难，第一种情况：通过在onTouch里面获取event.getX()坐标，而在这其中用到PointF类来保存x坐标，然后根据x坐标在onDraw()里面绘制即可；第二种情况：自动搜台，这其实很简单，开启子线程每Thread.sleep(200)就累加一定x值即可实现；

最后通过回调把计算好的值传递到Activity中，任务完成！

要是不太清楚回调原理的可看我另外一篇博客：Android回调与观察者模式的实现原理

下面贴上View的源码：

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;

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);
 }
 
 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%10 != 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%10 == 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();
 }
 
 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;
 }
 
 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));
 }
 
 public void setMaxLineCount(int count) {
 mMaxLineCount = count;
 }
 
 public void setAutoSearchFM(boolean isAuto){
 this.mIsAuto = isAuto;
 }
 
 public void startAutoSeachFM(){
 if(mIsAuto)
  new Thread(new SeachThread()).start();
 }
 
 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();
  }
 }
 }
 
 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);
 }
 }
 
}

贴上Activity代码：

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();
 }
 }
}

整个项目都放在GitHub上面了，欢迎做客与讨论：
https://github.com/xhunmon/RadioRule

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