前言：最近一直在学自定义View的相关知识，感觉这在Android中还是挺难的一块，当然这也是每个程序员必经之路，正好公司项目要求实现类似仪表盘的效果用于直观的显示公司数据，于是就简单的写了个demo，记录实现的过程。上篇《Android自定义View实现圆弧进度效果》简单记录了圆弧及文字的绘制，渐变色的仪表盘效果将更加升入的介绍canvas及paint的使用（如画布旋转，paint的渐变色设置等）。
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知识梳理
1.圆弧渐变色（SweepGradient）
2.圆弧上刻度绘制
3.指针指示当前数据位置（Bitmap）
4.数据文本跟随弧度显示（drawTextOnPath）
效果图：
1.继承自View
（1）重写构造方法，初始化Paint
public DashBoardView(Context context) {
this(context, null);
}
public DashBoardView(Context context, AttributeSet attrs) {
this(context, attrs, 0);
}
public DashBoardView(Context context, AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
init();
}初始化相关Paint
/**
* 初始化Paint
*/
private void init() {
//设置默认宽高值
defaultSize = dp2px(260);
//设置图片线条的抗锯齿
mPaintFlagsDrawFilter = new PaintFlagsDrawFilter
(0, Paint.ANTI_ALIAS_FLAG | Paint.FILTER_BITMAP_FLAG);
//最外层圆环渐变画笔设置
mOuterGradientPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
//设置圆环渐变色渲染
mOuterGradientPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.SRC_ATOP));
float position[] = {0.1f, 0.3f, 0.8f};
Shader mShader = new SweepGradient(width / 2, radius, mColors, position);
mOuterGradientPaint.setShader(mShader);
mOuterGradientPaint.setStrokeCap(Paint.Cap.ROUND);
mOuterGradientPaint.setStyle(Paint.Style.STROKE);
mOuterGradientPaint.setStrokeWidth(30);
//最外层圆环刻度画笔设置
mCalibrationPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mCalibrationPaint.setColor(Color.WHITE);
mCalibrationPaint.setStyle(Paint.Style.STROKE);
//中间圆环画笔设置
mMiddlePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mMiddlePaint.setStyle(Paint.Style.STROKE);
mMiddlePaint.setStrokeCap(Paint.Cap.ROUND);
mMiddlePaint.setStrokeWidth(5);
mMiddlePaint.setColor(GRAY_COLOR);
//内层圆环画笔设置
mInnerPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mInnerPaint.setStyle(Paint.Style.STROKE);
mInnerPaint.setStrokeCap(Paint.Cap.ROUND);
mInnerPaint.setStrokeWidth(4);
mInnerPaint.setColor(GRAY_COLOR);
PathEffect mPathEffect = new DashPathEffect(new float[]{5, 5, 5, 5}, 1);
mInnerPaint.setPathEffect(mPathEffect);
//外层圆环文本画笔设置
mTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mTextPaint.setColor(GRAY_COLOR);
mTextPaint.setTextSize(dp2px(12));
//中间文字画笔设置
mCenterTextPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mCenterTextPaint.setTextAlign(Paint.Align.CENTER);
//中间圆环进度画笔设置
mMiddleProgressPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mMiddleProgressPaint.setColor(GREEN_COLOR);
mMiddleProgressPaint.setStrokeCap(Paint.Cap.ROUND);
mMiddleProgressPaint.setStrokeWidth(5);
mMiddleProgressPaint.setStyle(Paint.Style.STROKE);
//指针图片画笔
mPointerBitmapPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
mPointerBitmapPaint.setColor(GREEN_COLOR);
//获取指针图片及宽高
mBitmap = BitmapFactory.decodeResource(getResources(), R.mipmap.pointer);
mBitmapHeight = mBitmap.getHeight();
mBitmapWidth = mBitmap.getWidth();
}注：
A、最外层圆弧的渐变色使用的是SweepGradient类实现的，SweepGradient继承自Shader；
B、注意渐变色的开始角度问题，如果跟圆弧起始角度不一致，记得使用矩阵转换进行旋转，再让paint去设置shader；
C、SweepGradient的第3个参数int[] colors必须包含两个及以上颜色值，不然会报错；
D、SweepGradient的第四个参数的数组大小必须和第三个参数的数组大小一样，也可以填入null。
（2）重写onMeasure,用于测量view宽高
onMeasure方法：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(remeasure(widthMeasureSpec, defaultSize),
remeasure(heightMeasureSpec, defaultSize));
}remeasure方法：
/**
* 根据传入的值进行重新测量
*/
public int remeasure(int measureSpec, int defaultSize) {
int result;
int specSize = MeasureSpec.getSize(measureSpec);
switch (MeasureSpec.getMode(measureSpec)) {
case MeasureSpec.UNSPECIFIED:
//未指定
result = defaultSize;
break;
case MeasureSpec.AT_MOST:
//设置warp_content时设置默认值
result = Math.min(specSize, defaultSize);
break;
case MeasureSpec.EXACTLY:
//设置math_parent 和设置了固定宽高值
result=specSize;
break;
default:
result = defaultSize;
}
return result;
}（3）重写onChange,用于获取view宽高
在onChange方法中获取当前View的宽高及获取圆弧的半径，初始化圆弧的RectF等
@Override
protected void onSizeChanged(int w, int h, int oldw, int oldh) {
super.onSizeChanged(w, h, oldw, oldh);
//确定View宽高
width = w;
height = h;
//圆环半径
radius = width / 2;
//外层圆环
float oval1 = radius - mOuterGradientPaint.getStrokeWidth() * 0.5f;
mOuterRectF = new RectF(-oval1, -oval1, oval1, oval1);
//中间和内层圆环
float oval2 = radius * 5 / 8;
float oval3 = radius * 3 / 4;
mInnerRectF = new RectF(-oval2 + dp2px(5), -oval2 + dp2px(5), oval2 - dp2px(5), oval2 - dp2px(5));
mMiddleRectF = new RectF(-oval3 + dp2px(10), -oval3 + dp2px(10), oval3 - dp2px(10), oval3 - dp2px(10));
//中间进度圆环
oval4 = radius * 6 / 8;
mMiddleProgressRectF = new RectF(-oval4+ dp2px(10), -oval4+ dp2px(10), oval4- dp2px(10), oval4- dp2px(10));
}（4）重写onDraw方法，用于绘制view
@SuppressLint("DrawAllocation")
@Override
protected void onDraw(Canvas canvas) {
//设置画布绘图无锯齿
canvas.setDrawFilter(mPaintFlagsDrawFilter);
//绘制圆弧
drawArc(canvas);
//绘制圆弧上的刻度
drawCalibration(canvas);
//绘制跟随圆弧path的文字
drawArcText(canvas);
//绘制圆弧中心文字
drawCenterText(canvas);
//绘制当前bitmap指针指示进度
drawBitmapProgress(canvas);
}2.Canvas绘制view
mStartAngle=105f，mEndAngle=250f
（1）绘制圆弧
/**
* 分别绘制外层 中间 内层圆环
*/
private void drawArc(Canvas canvas) {
canvas.save();
canvas.translate(width / 2, height / 2);
//画布旋转140°
canvas.rotate(140);
//最外层的渐变圆环
canvas.drawArc(mOuterRectF, -mStartAngle, -mEndAngle, false, mOuterGradientPaint);
//绘制内层虚线圆弧
canvas.drawArc(mInnerRectF, -mStartAngle, -mEndAngle, false, mInnerPaint);
//绘制中间圆弧
canvas.drawArc(mMiddleRectF, -mStartAngle, -mEndAngle, false, mMiddlePaint);
canvas.restore();
}（2）绘制渐变色圆弧上的大小刻度
/**
* 绘制外层渐变色圆弧上的大小刻度线
*/
private void drawCalibration(Canvas canvas) {
int dst = (int) (2 * radius - mOuterGradientPaint.getStrokeWidth());
for (int i = 0; i <= 40; i++) {
canvas.save();
canvas.rotate(-(-30 + 6 * i), radius, radius);
if (i % 10 == 0) {
mCalibrationPaint.setStrokeWidth(4);
//绘制大刻度
canvas.drawLine(dst, radius, 2 * radius, radius, mCalibrationPaint);
} else {
//小刻度
mCalibrationPaint.setStrokeWidth(1);
canvas.drawLine(dst, radius, 2 * radius, radius, mCalibrationPaint);
}
canvas.restore();
}
}注：
A、圆弧的总弧度为240f，循环40次
B、小刻度每次旋转6弧度，每绘制10次小刻度就会绘制一次大刻度，即大刻度每次旋转60弧度
（3）绘制跟随圆弧弧度描述文字
/**
* 绘制跟随圆弧弧度的文本
*/
private void drawArcText(Canvas canvas) {
canvas.save();
//每次旋转角度
int rotateAngle = 30;
//旋转画布
canvas.rotate(-118, radius - dp2px(26), radius-dp2px(103));
for (int i = 0; i < valueList.size(); i++) {
//计算起始角度
int startAngle = 30 * i - 108;
//设置数据跟着圆弧绘制
Path paths = new Path();
paths.addArc(mInnerRectF, startAngle, rotateAngle);
float textLen = mTextPaint.measureText(valueList.get(i));
canvas.drawTextOnPath(valueList.get(i), paths, -textLen / 2 + dp2px(20), -dp2px(22), mTextPaint);
//canvas.drawText(text[i], radius - 10, radius * 3 / 16+dp2px(10), mTextPaint);
}
canvas.restore();
}注：
A、drawTextOnPath为文字随path路径显示，drawTextOnPath的第3个参数hOffset为文字水平方向的偏移量，第4个参数vOffset为文字垂直方向的偏移量；
B、重点是画布开始时的旋转角度及不同文字的起始角度
（4）绘制圆弧中心的数据及描述信息
/**
* 绘制圆弧中间的文本内容
*/
private void drawCenterText(Canvas canvas) {
//绘制当前数据值
mCenterTextPaint.setColor(GREEN_COLOR);
mCenterTextPaint.setTextSize(dp2px(25));
mCenterTextPaint.setStyle(Paint.Style.STROKE);
canvas.drawText(String.valueOf(mAnimatorValue), radius, radius, mCenterTextPaint);
//绘制当前数据描述
mCenterTextPaint.setTextSize(dp2px(20));
canvas.drawText(mCurrentDes, radius, radius + dp2px(25), mCenterTextPaint);
}（5）绘制当前数值对应的圆弧及指针图片指示
/**
* 绘制当前进度和指示图片
*/
private void drawBitmapProgress(Canvas canvas) {
//如果当前角度为0，则不绘制指示图片
if (mCurrentAngle==0f){
return;
}
canvas.save();
canvas.translate(radius, radius);
canvas.rotate(270);
//绘制对应的圆弧
canvas.drawArc(mMiddleProgressRectF, -mStartAngle-20, mCurrentAngle+5, false, mMiddleProgressPaint);
canvas.rotate(60 + mCurrentAngle);
//利用矩阵平移使图片指针方向始终指向刻度
Matrix matrix = new Matrix();
matrix.preTranslate(-oval4 - mBitmapWidth * 3 / 8 + 10, -mBitmapHeight / 2);
canvas.drawBitmap(mBitmap, matrix, mPointerBitmapPaint);
canvas.restore();
}注：为了使指针图片的指针一直指向刻度盘上的刻度，这里使用了矩阵的平移。
3.添加动画及数据
（1）动画效果
/**
* 当前数据对应弧度旋转及当前数据自增动画
*/
public void startRotateAnim() {
ValueAnimator mAngleAnim = ValueAnimator.ofFloat(mCurrentAngle, mTotalAngle);
mAngleAnim.setInterpolator(new AccelerateDecelerateInterpolator());
mAngleAnim.setDuration(2500);
mAngleAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator valueAnimator) {
mCurrentAngle = (float) valueAnimator.getAnimatedValue();
postInvalidate();
}
});
mAngleAnim.start();
ValueAnimator mNumAnim = ValueAnimator.ofInt(mAnimatorValue, mCurrentValue);
mNumAnim.setDuration(2500);
mNumAnim.setInterpolator(new LinearInterpolator());
mNumAnim.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
@Override
public void onAnimationUpdate(ValueAnimator valueAnimator) {
mAnimatorValue = (int) valueAnimator.getAnimatedValue();
postInvalidate();
}
});
mNumAnim.start();
}（2）设置数据及描述信息
/**
* 设置数据
*/
public void setValues(int values, List valueList) {
this.valueList=valueList;
if (values <= 0) {
mCurrentValue = values;
mTotalAngle = 0f;
mCurrentDes = "";
} else if (values <= 14000) {
mCurrentValue = values;
mTotalAngle = values / 14000f * 60-2;
Log.e("rcw","mTotalAngle="+mTotalAngle);
mCurrentDes = "基础目标";
} else if (values>14000&&values <= 17000) {
mCurrentValue = values;
mCurrentDes = "测试目标";
mTotalAngle = values / 17000f * 120-2;
} else if (values>17000&&values <= 21000) {
mCurrentValue = values;
mTotalAngle = values / 21000f * 180-2;
mCurrentDes = "保底目标";
} else {
mCurrentValue=values;
float ratio=values / 21000f;
if (ratio<20){
mTotalAngle = ratio+180;
}else {
mTotalAngle = (float) (ratio*0.2+200);
}
mCurrentDes = "冲刺目标";
}
startRotateAnim();
}
总结：自定义View实现仪表盘效果用到了canvas的旋转及矩阵平移；drawTextOnpath使的文字跟随path绘制；SweepGradient实现圆弧的渐变色效果。
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创新互联。
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