Android实现渐变色的圆弧虚线效果

首先来看看效果图：

1，SweepGradient(梯度渲染)

public SweepGradient (float cx, float cy, int[] colors, float[] positions)

扫描渲染，就是以某个点位中心旋转一周所形成的效果！参数依次是：

      cx：扫描的中心x坐标

      cy：扫描的中心y坐标

      colors：梯度渐变的颜色数组

      positions：指定颜色数组的相对位置

public static final int[] SWEEP_GRADIENT_COLORS = new int[]{Color.GREEN, Color.GREEN, Color.BLUE, Color.RED, Color.RED};
mColorShader = new SweepGradient(radius, radius,SWEEP_GRADIENT_COLORS,null);

效果图：

SweepGradient

2，DashPathEffect(Path的线段虚线化)

DashPathEffect(float[] intervals, float phase)

      intervals：为虚线的ON和OFF的数组，数组中元素数目需要 >= 2

      phase：为绘制时的偏移量

//计算路径的长度
PathMeasure pathMeasure = new PathMeasure(mPath, false);
float length = pathMeasure.getLength();
float step = length / 60;
dashPathEffect = new DashPathEffect(new float[]{step / 3, step * 2 / 3}, 0);

效果图：

DashPathEffect

3，下面是全部的代码：

package com.example.yyw.xfermodedemo;
import android.animation.ValueAnimator;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.DashPathEffect;
import android.graphics.Paint;
import android.graphics.Path;
import android.graphics.PathMeasure;
import android.graphics.RectF;
import android.graphics.SweepGradient;
import android.util.AttributeSet;
import android.view.View;

public class OilTableLine extends View {
 public static final int[] SWEEP_GRADIENT_COLORS = new int[]{Color.GREEN, Color.GREEN, Color.BLUE, Color.RED, Color.RED};
 private int tableWidth = 50;
 private Paint mPaint;
 private Path mPath;
 private RectF mTableRectF;
 //把路径分成虚线段的
 private DashPathEffect dashPathEffect;
 //给路径上色
 private SweepGradient mColorShader;
 //指针的路径
 private Path mPointerPath;
 private float mCurrentDegree = 60;
 public OilTableLine(Context context, AttributeSet attrs) {
  super(context, attrs);
  mPaint = new Paint();
  mPaint.setAntiAlias(true);
  mPaint.setDither(true);
  mPaint.setColor(Color.BLACK);
  mPath = new Path();
  mPointerPath = new Path();
  startAnimator();
 }
 @Override
 protected void onSizeChanged(int w, int h, int oldw, int oldh) {
  super.onSizeChanged(w, h, oldw, oldh);
  float size = Math.min(w, h) - tableWidth * 2;
  //油表的位置方框
  mTableRectF = new RectF(0, 0, size, size);
  mPath.reset();
  //在油表路径中增加一个从起始弧度
  mPath.addArc(mTableRectF, 60, 240);
  //计算路径的长度
  PathMeasure pathMeasure = new PathMeasure(mPath, false);
  float length = pathMeasure.getLength();
  float step = length / 60;
  dashPathEffect = new DashPathEffect(new float[]{step / 3, step * 2 / 3}, 0);
  float radius = size / 2;
  mColorShader = new SweepGradient(radius, radius,SWEEP_GRADIENT_COLORS,null);
  //设置指针的路径位置
  mPointerPath.reset();
  mPointerPath.moveTo(radius, radius - 20);
  mPointerPath.lineTo(radius, radius + 20);
  mPointerPath.lineTo(radius * 2 - tableWidth, radius);
  mPointerPath.close();
 }
 @Override
 protected void onDraw(Canvas canvas) {
  super.onDraw(canvas);
  float dx = (getWidth() - mTableRectF.width()) / 2;
  float dy = (getHeight() - mTableRectF.height()) / 2;
  //把油表的方框平移到正中间
  canvas.translate(dx, dy);
  canvas.save();
  //旋转画布
  canvas.rotate(90, mTableRectF.width() / 2, mTableRectF.height() / 2);
  mPaint.setStyle(Paint.Style.STROKE);
  mPaint.setStrokeWidth(tableWidth);
  mPaint.setPathEffect(dashPathEffect);
  mPaint.setShader(mColorShader);
  canvas.drawPath(mPath, mPaint);
  canvas.restore();
  //还原画笔
  mPaint.setPathEffect(null);
  mPaint.setShader(null);
  mPaint.setStyle(Paint.Style.FILL);
  mPaint.setStrokeWidth(tableWidth / 10);
  canvas.save();
  canvas.rotate(150 + mCurrentDegree, mTableRectF.width() / 2, mTableRectF.height() / 2);
  canvas.drawPath(mPointerPath, mPaint);
  canvas.restore();
 }
 public void startAnimator() {
  ValueAnimator animator = ValueAnimator.ofFloat(0, 240);
  animator.setDuration(40000);
  animator.setRepeatCount(ValueAnimator.INFINITE);
  animator.setRepeatMode(ValueAnimator.RESTART);
  animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
   @Override
   public void onAnimationUpdate(ValueAnimator animation) {
    mCurrentDegree = (int) (0 + (Float) animation.getAnimatedValue());
    invalidate();
   }
  });
  animator.start();
 }
}

总结

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