Android技术分享| 自定义View实现使用更方便的SeekBar
前言
Android中自带的SeekBar个人感觉用起来很麻烦，调整一些颜色之类的需要单独写一个XML文件，内容感觉也很啰嗦。刚好我们的白板Demo开发中需要用到SeekBar，所以干脆实现了一个满足基本功能的SeekBar，支持在xml布局中指定各种颜色属性，也支持代码动态设置颜色。用起来更顺心一些。
SeekBar的代码请查看Github地址：白板Demo，Demo地址请：点击这里 即拿即用，非常方便;p（记得将res/values/styles.xml中的属性一并复制走）
效果
实现
由于不涉及到动画，这种自定义View做起来还是相当简单的。首先在res/values/styles.xml文件中定义好自己需要的属性，我这里贴上我定义的属性：
<declare-styleable name="SeekBarWidget"> <attr name="seek_maxProgress" format="integer" /><!-- 最大progress --> <attr name="seek_minProgress" format="integer" /><!-- 最小progress --> <attr name="seek_progress" format="integer" /><!-- 当前progress(默认值) --> <attr name="seek_circleRadius" format="dimension" /><!-- seekBar中间圆形的半径 --> <attr name="seek_circleStrokeWidth" format="dimension" /><!-- seekBar中间圆形外的border --> <attr name="seek_lineHeight" format="dimension" /><!-- lineHeight有点词不达意，其实是进度条的高度 --> <attr name="seek_backgroundColor" format="color" /><!-- 进度条的背景色 --> <attr name="seek_circleStrokeColor" format="color" /><!-- border的颜色 --> <attr name="seek_maxColor" format="color" /><!-- 进度条的前景色 --> <attr name="seek_startColor" format="color" /><!-- 如果需要渐变色则设置此属性，否则这条属性置空即可 --> </declare-styleable> 复制代码
属性定义好以后，在View的构造中解析一下：
public SeekBarWidget(Context context) { this(context, null); } public SeekBarWidget(Context context, @Nullable AttributeSet attrs) { this(context, attrs, 0); } public SeekBarWidget(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); if (null != attrs) { TypedArray typedArray = getResources().obtainAttributes(attrs, R.styleable.SeekBarWidget); minProgress = typedArray.getInt(R.styleable.SeekBarWidget_seek_minProgress, 0); maxProgress = typedArray.getInt(R.styleable.SeekBarWidget_seek_maxProgress, 100) - minProgress; progress = typedArray.getInt(R.styleable.SeekBarWidget_seek_progress, 0) - minProgress; if (progress < 0) progress = minProgress; circleRadius = typedArray.getDimension(R.styleable.SeekBarWidget_seek_circleRadius, 20f); circleStrokeWidth = typedArray.getDimension(R.styleable.SeekBarWidget_seek_circleStrokeWidth, 5f); lineHeight = typedArray.getDimension(R.styleable.SeekBarWidget_seek_lineHeight, 5f); backgroundColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_backgroundColor, Color.parseColor("#F0F0F0")); circleStrokeColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_circleStrokeColor, Color.WHITE); int maxColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_maxColor, Color.RED); int startColor = typedArray.getColor(R.styleable.SeekBarWidget_seek_startColor, maxColor); colorTransition = new ColorTransition(startColor, maxColor); typedArray.recycle(); percentage = progress * 1.0f / maxProgress; horizontalPadding = circleRadius * 2 + circleStrokeWidth * 2 + getPaddingStart() + getPaddingEnd(); mPaddingLeft = horizontalPadding - getPaddingEnd() - circleRadius - circleStrokeWidth; return; } maxProgress = 100; minProgress = 0; circleRadius = 20; circleStrokeWidth = 5; lineHeight = 5; backgroundColor = Color.parseColor("#F0F0F0"); colorTransition = new ColorTransition(Color.WHITE, Color.RED); circleStrokeColor = Color.WHITE; horizontalPadding = circleRadius * 2 + circleStrokeWidth * 2 + getPaddingStart() + getPaddingEnd(); mPaddingLeft = horizontalPadding - getPaddingEnd() - circleRadius - circleStrokeWidth; } 复制代码接下来是onMeasure和onDraw，由于我的应用场景宽高已经固定好了，所以没有写onMeasure，有需求的朋友可以自己实现一下～ 而绘制的思路很简单：
先绘制一条背景色的线，线的高度由外部指定。（设置StrokeCap为ROUND）
再绘制一条前景色的线，线高度同样由外部指定，这里我读取的是同一个属性
lineHeight，也可以根据需求不同设置不一样的高度;p接下来绘制seekBar的圆，这里border也直接使用
drawCircle来实现，先绘制border。(circleRadius + circleStrokeWidth / 2f)最后绘制中间的圆
onDraw:
@Override protected void onDraw(Canvas canvas) { final int width = (int) (getMeasuredWidth() - horizontalPadding); final int height = getMeasuredHeight(); paint.setColor(backgroundColor); paint.setStrokeWidth(lineHeight); paint.setStyle(Paint.Style.FILL_AND_STROKE); paint.setStrokeCap(Paint.Cap.ROUND); canvas.drawLine(mPaddingLeft, height >> 1, mPaddingLeft + width, height >> 1, paint); //float percentage = progress / maxProgress; int currColor = colorTransition.getValue(percentage); paint.setColor(currColor); canvas.drawLine(mPaddingLeft, height >> 1, mPaddingLeft + width * percentage, height >> 1, paint); // draw circle border paint.setColor(circleStrokeColor); canvas.drawCircle(mPaddingLeft + width * percentage, height >> 1, circleRadius + (circleStrokeWidth / 2f), paint); // draw circle inside color paint.setColor(currColor); canvas.drawCircle(mPaddingLeft + width * percentage, height >> 1, circleRadius, paint); } 复制代码最后，处理一下onTouch事件。思路也很简单，从down、move、up事件中判断一下是否为横向滚动，是的话计算一下距离，更改progress进度并通知View重新绘制即可：
private float downX; private float downY; @Override public boolean onTouchEvent(MotionEvent event) { boolean intercept = false; switch (event.getAction()) { case MotionEvent.ACTION_DOWN: downX = event.getX(); downY = event.getY(); intercept = true; break; case MotionEvent.ACTION_MOVE: float moveX = event.getX(); float moveY = event.getY(); float xMove = Math.abs(moveX - downX) - Math.abs(moveY - downY); if (xMove > 0f) { float hX = moveX - downX; boolean toLeft = hX < 0.0f; float movePercent = Math.abs(hX) / getMeasuredWidth(); if (percentage < 1.0f && !toLeft) { percentage += movePercent; } else if (percentage > 0f && toLeft) { percentage -= movePercent; } if (percentage < 0f) percentage = 0f; if (percentage > 1f) percentage = 1f; progress = (int) Math.floor(percentage * maxProgress); } intercept = true; downX = moveX; downY = moveY; postInvalidate(); if (null != mListener && beforeProgress != getProgress()) { beforeProgress = getProgress(); mListener.onProgress(getProgress()); } break; case MotionEvent.ACTION_UP: break; } return intercept || super.onTouchEvent(event); //return true; } @Override public boolean dispatchTouchEvent(MotionEvent event) { getParent().requestDisallowInterceptTouchEvent(true); return super.dispatchTouchEvent(event); } 复制代码OK，一个复制即用的自定义SeekBar便完成了。比官方原版的SeekBar使用起来顺眼多了(｢・ω・)｢
(欢迎下载Demo玩一玩！Demo地址)
作者：anyRTC
链接：https://juejin.cn/post/7054376809931997214