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：

/**

* 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%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;

/**

* 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 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%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();

}

/**

* 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);

}

}

/******************************************************************/

}

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();

}

}

}

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持脚本之家。