Android 系统自带的 ProgressBar 几乎都不能满足我们的日常开发，导致我们在开发的时候经常要自己定一个进度条

本章节我们就来实现最常见的圆环进度条，先来看看最后的效果

1. 创建一个 空的 Android 项目 cn.twle.android.ProgressBarCustom

2. 自定义一个 View 类 RingProgressBar.java

   package cn.twle.android.progressbarcustom;
   
   import android.content.Context;
   import android.graphics.Canvas;
   import android.graphics.Color;
   import android.graphics.Paint;
   import android.graphics.RectF;
   import android.util.AttributeSet;
   import android.view.View;
   
   public class RingProgressBar extends View {
   
       private Paint mBackPaint;
       private Paint mFrontPaint;
       private Paint mTextPaint;
       private float mStrokeWidth = 50;
       private float mHalfStrokeWidth = mStrokeWidth / 2;
       private float mRadius = 200;
       private RectF mRect;
       private int mProgress = 0;
       //目标值，想改多少就改多少
       private int mTargetProgress = 90;
       private int mMax = 100;
       private int mWidth;
       private int mHeight;
   
       public RingProgressBar(Context context) {
           super(context);
           init();
       }
   
       public RingProgressBar(Context context, AttributeSet attrs) {
           super(context, attrs);
           init();
       }
   
       public RingProgressBar(Context context, AttributeSet attrs, int defStyleAttr) {
           super(context, attrs, defStyleAttr);
           init();
       }
   
       //完成相关参数初始化
       private void init() {
           mBackPaint = new Paint();
           mBackPaint.setColor(Color.WHITE);
           mBackPaint.setAntiAlias(true);
           mBackPaint.setStyle(Paint.Style.STROKE);
           mBackPaint.setStrokeWidth(mStrokeWidth);
   
           mFrontPaint = new Paint();
           mFrontPaint.setColor(Color.GREEN);
           mFrontPaint.setAntiAlias(true);
           mFrontPaint.setStyle(Paint.Style.STROKE);
           mFrontPaint.setStrokeWidth(mStrokeWidth);
   
           mTextPaint = new Paint();
           mTextPaint.setColor(Color.GREEN);
           mTextPaint.setAntiAlias(true);
           mTextPaint.setTextSize(80);
           mTextPaint.setTextAlign(Paint.Align.CENTER);
       }
   
       // 重写测量大小的 onMeasure 方法
       @Override
       protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
           super.onMeasure(widthMeasureSpec, heightMeasureSpec);
           mWidth = getRealSize(widthMeasureSpec);
           mHeight = getRealSize(heightMeasureSpec);
           setMeasuredDimension(mWidth, mHeight);
   
       }
   
       // 重写绘制 View 的核心方法 onDraw()
       @Override
       protected void onDraw(Canvas canvas) {
           initRect();
           float angle = mProgress / (float) mMax * 360;
           canvas.drawCircle(mWidth / 2, mHeight / 2, mRadius, mBackPaint);
           canvas.drawArc(mRect, -90, angle, false, mFrontPaint);
           canvas.drawText(mProgress + "%", mWidth / 2 + mHalfStrokeWidth, mHeight / 2 + mHalfStrokeWidth, mTextPaint);
           if (mProgress < mTargetProgress) {
               mProgress += 1;
               invalidate();
           }
   
       }
   
       public int getRealSize(int measureSpec) {
           int result = 1;
           int mode = MeasureSpec.getMode(measureSpec);
           int size = MeasureSpec.getSize(measureSpec);
   
           if (mode == MeasureSpec.AT_MOST || mode == MeasureSpec.UNSPECIFIED) {
               //自己计算
               result = (int) (mRadius * 2 + mStrokeWidth);
           } else {
               result = size;
           }
   
           return result;
       }
   
       private void initRect() {
           if (mRect == null) {
               mRect = new RectF();
               int viewSize = (int) (mRadius * 2);
               int left = (mWidth - viewSize) / 2;
               int top = (mHeight - viewSize) / 2;
               int right = left + viewSize;
               int bottom = top + viewSize;
               mRect.set(left, top, right, bottom);
           }
       }
   
   }
   

3. 然后修改 activity_main.xml 添加我们的 RingProgressBar

   <com.jay.progressbardemo.CirclePgBar
           android:layout_width="match_parent"
           android:layout_height="match_parent"/>
   

参考文档

官方 API 文档： ProgressBar