最近做了一个功能，里面涉及到了渐变圆形的需求。就是一个颜色可以渐变的圆环，最后实现的效果如下图：
左图是带渐变效果，右图是不带渐变效果。原理还是绘图，Canvas可以绘制的对象有：弧线(arcs)、填充颜色(argb和color)、
Bitmap、圆(circle和oval)、点(point)、线(line)、矩形(Rect)、图片(Picture)、圆角矩形 (RoundRect)、文本(text)、
顶点(Vertices)、路径(path)。通过组合这些对象我们可以画出一些简单有趣的界面出来，但是光有这些功能还是不够的，
如果我要画一个仪表盘(数字围绕显示在一个圆圈中)呢？ 幸好Android还提供了一些对Canvas位置转换的方法：rorate、scale、
translate、skew(扭曲)等，而且它允许你通过获得它的转换矩阵对象(getMatrix方法，不知道什么是转换矩阵？)
直接操作它。这些操作就像是虽然你的笔还是原来的地方画，但是画纸旋转或者移动了，所以你画的东西的方位就产生变化。
为了方便一些转换操作，Canvas 还提供了保存和回滚属性的方法(save和restore)，比如你可以先保存目前画纸的位置(save)，
然后旋转90度，向下移动100像素后画一些图形，画完后调用restore方法返回到刚才保存的位置。
话不多说，上代码
核心类：
自定义控件 CircleProgressBar
package com.jky.mobile_xmxt.view; import android.content.Context; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import android.graphics.RectF; import android.graphics.SweepGradient; import android.util.AttributeSet; import android.view.View; import android.view.animation.Animation; import android.view.animation.Transformation; import com.jky.mobile_xmxt.R; import java.text.DecimalFormat; /** * 圆盘计步图表 */ public class CircleProgressBar extends View { private RectF mWheelRect = new RectF(); private Paint mDefaultWheelPaint; private Paint mFinishWheelPaint; private Paint mCenterWheelPaint; private Paint mTitlePaint, mStepPaint, mTargetPaint; private float mCircleStrokeWidth; private float mSweepAnglePer; private float mPercent; private int mStepNum, mCurrStepNum; private float pressExtraStrokeWidth; private BarAnimation mAnim; private int mMaxStepNum;// 默认最大步数 private float mTitleY, mStepY, mTargetY; private DecimalFormat mDecimalFormat = new DecimalFormat("#.0");// 格式为保留小数点后一位 public static String GOAL_STEP; public static String PERCENT; public CircleProgressBar(Context context) { super(context); init(null, 0); } public CircleProgressBar(Context context, AttributeSet attrs) { super(context, attrs); init(attrs, 0); } public CircleProgressBar(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(attrs, defStyle); } private void init(AttributeSet attrs, int defStyle) { mFinishWheelPaint = new Paint(); mFinishWheelPaint.setColor(Color.rgb(100, 113, 205)); mFinishWheelPaint.setStyle(Paint.Style.STROKE);// 空心 mFinishWheelPaint.setStrokeCap(Paint.Cap.ROUND);// 圆角画笔 mFinishWheelPaint.setAntiAlias(true);// 去锯齿 mCenterWheelPaint = new Paint(); mCenterWheelPaint.setColor(Color.rgb(243, 243, 243)); mCenterWheelPaint.setStyle(Paint.Style.STROKE); mCenterWheelPaint.setStrokeCap(Paint.Cap.ROUND); mCenterWheelPaint.setAntiAlias(true); mDefaultWheelPaint = new Paint(); mDefaultWheelPaint.setColor(Color.rgb(127, 127, 127)); mDefaultWheelPaint.setStyle(Paint.Style.STROKE); mDefaultWheelPaint.setStrokeCap(Paint.Cap.ROUND); mDefaultWheelPaint.setAntiAlias(true); mTitlePaint = new Paint(); mTitlePaint.setAntiAlias(true); mTitlePaint.setColor(Color.WHITE); mStepPaint = new Paint(); mStepPaint.setAntiAlias(true); mStepPaint.setColor(Color.WHITE); mTargetPaint = new Paint(); mTargetPaint.setAntiAlias(true); mTargetPaint.setColor(Color.WHITE); mAnim = new BarAnimation(); } @Override protected void onDraw(Canvas canvas) { canvas.drawArc(mWheelRect, 0, 359, false, mDefaultWheelPaint); canvas.drawArc(mWheelRect, 0, 359, false, mCenterWheelPaint); canvas.drawArc(mWheelRect, 90, mSweepAnglePer, false, mFinishWheelPaint); // canvas.drawText("步数", mWheelRect.centerX() - (mTitlePaint.measureText("步数") / 2), mTitleY, // mTitlePaint); canvas.drawText(mCurrStepNum + "", mWheelRect.centerX() - (mStepPaint.measureText(String.valueOf(mCurrStepNum)) / 2), mStepY, mStepPaint); String description = ""; float percent = getPercent(); if(percent > 0.5){ description ="严重污染"; }else if(percent<0.5){ description ="中等污染"; }else{ description ="普通污染"; } canvas.drawText(description , mWheelRect.centerX() - (mTargetPaint.measureText(description) / 2), mTargetY, mTargetPaint); SweepGradient sweepGradient = new SweepGradient(mWheelRect.centerX(), mWheelRect.centerY(), new int[]{getResources().getColor(R.color.color_environment_severe), getResources().getColor(R.color.color_environment_serious), getResources().getColor(R.color.color_environment_excellent), getResources().getColor(R.color.color_environment_good), getResources().getColor(R.color.color_environment_mild), getResources().getColor(R.color.color_environment_moderate)}, null); mFinishWheelPaint.setShader(sweepGradient); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { int height = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec); int width = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec); int min = Math.min(width, height);// 获取View最短边的长度 setMeasuredDimension(min, min);// 强制改View为以最短边为长度的正方形 mCircleStrokeWidth = getTextScale(15, min);// 圆弧的宽度 pressExtraStrokeWidth = getTextScale(10, min);// 圆弧离矩形的距离 mWheelRect.set(mCircleStrokeWidth + pressExtraStrokeWidth, mCircleStrokeWidth + pressExtraStrokeWidth, min - mCircleStrokeWidth - pressExtraStrokeWidth, min - mCircleStrokeWidth - pressExtraStrokeWidth);// 设置矩形 mTitlePaint.setTextSize(getTextScale(60, min)); mStepPaint.setTextSize(getTextScale(120, min)); mTargetPaint.setTextSize(getTextScale(40, min)); mTitleY = getTextScale(170, min); mStepY = getTextScale(300, min); mTargetY = getTextScale(380, min); mFinishWheelPaint.setStrokeWidth(mCircleStrokeWidth); mCenterWheelPaint.setStrokeWidth(mCircleStrokeWidth); mDefaultWheelPaint.setStrokeWidth(mCircleStrokeWidth - getTextScale(2, min)); mDefaultWheelPaint.setShadowLayer(getTextScale(10, min), 0, 0, Color.rgb(127, 127, 127));// 设置阴影 } /** * 进度条动画 * * @author Administrator */ public class BarAnimation extends Animation { /** * 每次系统调用这个方法时， 改变mSweepAnglePer，mPercent，stepnumbernow的值， * 然后调用postInvalidate()不停的绘制view。 */ @Override protected void applyTransformation(float interpolatedTime, Transformation t) { // if (interpolatedTime < 1.0f) { // mPercent = Float.parseFloat(mDecimalFormat.format(interpolatedTime * mStepNum * 100f / mMaxStepNum));// 将浮点值四舍五入保留一位小数 // mSweepAnglePer = interpolatedTime * mStepNum * 360 / mMaxStepNum; // mCurrStepNum = (int) (interpolatedTime * mStepNum); // } else { mPercent = Float.parseFloat(mDecimalFormat.format(mStepNum * 100f / mMaxStepNum));// 将浮点值四舍五入保留一位小数 if (mPercent > 100.0f) { mPercent = 100.0f; } PERCENT = String.valueOf(mPercent); mSweepAnglePer = mStepNum * 360 / mMaxStepNum; mCurrStepNum = mStepNum; // } requestLayout(); } } public float getPercent() { return mPercent; } /** * 根据控件的大小改变绝对位置的比例 * * @param n * @param m * @return */ public float getTextScale(float n, float m) { return n / 500 * m; } /** * 更新步数和设置一圈动画时间 * * @param stepCount * @param time */ public void update(int stepCount, int time) { this.mStepNum = stepCount; mAnim.setDuration(time); // setAnimationTime(time); this.startAnimation(mAnim); } /** * @param stepNum */ public void setMaxStepNum(int stepNum) { mMaxStepNum = stepNum; GOAL_STEP = String.valueOf(mMaxStepNum); } public void setColor(int color) { mFinishWheelPaint.setColor(color); mStepPaint.setColor(color); } /** * 设置动画时间 * * @param time */ public void setAnimationTime(int time) { mAnim.setDuration(time * mStepNum / mMaxStepNum);// 按照比例设置动画执行时间 } }
xml引用
<com.jky.mobile_xmxt.view.CircleProgressBar android:id="@+id/color_progress_view" android:layout_width="match_parent" android:layout_height="0dp" android:layout_weight="6" />
Activity调用方法
color_progress_view = (CircleProgressBar)view.findViewById(R.id.color_progress_view); color_progress_view.setMaxStepNum(500); color_progress_view.update(470,1000);
由于和调用其他控件方法类似，姑且省去了很多其他业务逻辑代码，代码不是特别复杂，修改起来也很方便（修改颜色，总量及比例等），所以只粘贴核心相关的代码，希望可以帮助到大家。
