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

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。

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。