1. 思路分析

自定义View步骤：
1>：values__attrs.xml，自定义属性；
2>：在第三个构造方法中，获取自定义属性；
3>：onMeasure：不是非必须的，测量控件大小；
4>：onDraw：所有绘制代码都写在onDraw方法中；

思路分析
1>：自定义属性：内圆颜色、外圆颜色、圆弧宽度、中间文字颜色、文字大小；
2>：自定义ProgressBar，继承View；

2. 效果图如下

3. 代码如下

1>：attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <declare-styleable name="ProgressBar">
        <attr name="innerBackground" format="color"/>
        <attr name="outterBackground" format="color"/>
        <attr name="roundWidth" format="dimension"/>
        <attr name="progressTextSize" format="dimension"/>
        <attr name="progressTextColor" format="color"/>
    </declare-styleable>
</resources>

2>：ProgressBar

package com.example.view05_day;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.graphics.RectF;
import android.util.AttributeSet;
import android.util.TypedValue;
import android.view.View;

import androidx.annotation.Nullable;

public class ProgressBar extends View {
    private int innerColor = Color.BLACK;
    private int outColor = Color.RED;
    private int mTextSize = 15;
    private int mTextColor = Color.BLACK;
    private int mRoundWidth = 20;
    private int currentProgress = 50;
    private int maxNum = 100;

    private Paint innerPaint, outerPaint, mPaintText;

    public ProgressBar(Context context) {
        this(context, null);
    }

    public ProgressBar(Context context, @Nullable @org.jetbrains.annotations.Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ProgressBar(Context context, @Nullable @org.jetbrains.annotations.Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        TypedArray array = context.obtainStyledAttributes(attrs, R.styleable.ProgressBar);
        innerColor = array.getColor(R.styleable.ProgressBar_innerBackground, innerColor);
        outColor = array.getColor(R.styleable.ProgressBar_outterBackground, outColor);
        mTextSize = array.getDimensionPixelSize(R.styleable.ProgressBar_progressTextSize,sp2px(mTextSize));
        mRoundWidth = (int)array.getDimension(R.styleable.ProgressBar_roundWidth, dip2px(mRoundWidth));
        mTextColor = array.getColor(R.styleable.ProgressBar_progressTextColor, mTextColor);
        array.recycle();

        innerPaint = new Paint();
        innerPaint.setAntiAlias(true);
        innerPaint.setColor(innerColor);
        innerPaint.setStrokeWidth(mRoundWidth);
        innerPaint.setStyle(Paint.Style.STROKE);

        outerPaint = new Paint();
        outerPaint.setAntiAlias(true);
        outerPaint.setColor(outColor);
        outerPaint.setStrokeWidth(mRoundWidth);
        outerPaint.setStyle(Paint.Style.STROKE);

        mPaintText = new Paint();
        mPaintText.setAntiAlias(true);
        mPaintText.setColor(mTextColor);
        mPaintText.setTextSize(mTextSize);
    }

    private int sp2px(int sp) {
        return (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp, getResources().getDisplayMetrics());
    }

    private int dip2px(int dip) {
        return (int)TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dip, getResources().getDisplayMetrics());
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        //只保证正方形
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        setMeasuredDimension(Math.min(width, height), Math.min(width, height));
    }

    @Override
    protected void onDraw(Canvas canvas) {
        //先画内圆
        int center = getWidth()/2;
        int radius = center - mRoundWidth/2;
        canvas.drawCircle(center,center,radius,innerPaint);

        //再画外圆，画圆弧
        RectF rectF = new RectF(0+mRoundWidth/2,0+mRoundWidth/2,getWidth()-mRoundWidth/2,getHeight()-mRoundWidth/2);
        if (currentProgress == 0) {
            return;
        }
        float percent = (float)currentProgress/maxNum;
        canvas.drawArc(rectF,0, 360 * percent, false, outerPaint);

        //画进度文字
        String text = ((int)(percent * 100)) + "%";
        Rect bounds = new Rect();
        mPaintText.getTextBounds(text,0,text.length(),bounds);
        int x = getWidth()/2 - bounds.width()/2;
        Paint.FontMetrics fontMetrics = mPaintText.getFontMetrics();
        int dy = (int)((fontMetrics.bottom - fontMetrics.top)/2 - fontMetrics.bottom);
        int baseline = getHeight()/2 + dy;
        canvas.drawText(text,x,baseline,mPaintText);
    }

    //给几个方法
    public synchronized void setMax (int max) throws IllegalArgumentException{
        if (max < 0) {
            throw new IllegalArgumentException("FUCK YOU");
        }
        this.maxNum = max;
    }

    public synchronized void setProgress (int progress) throws IllegalArgumentException{
        if (progress < 0) {
            throw new IllegalArgumentException("progress error");
        }
        this.currentProgress = progress;
        invalidate();
    }
}

3>activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:paddingTop="16dp"
    tools:context=".MainActivity">

    <com.example.view05_day.ProgressBar
        android:id="@+id/ProgressBar"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:progressTextColor="@color/teal_700"
        app:innerBackground= "@color/black"
        app:outterBackground="@color/purple_200"
        app:progressTextSize="20dp"
        app:roundWidth = "20dp"/>
</RelativeLayout>

4>：MainActivity.java

package com.example.view05_day;

import androidx.appcompat.app.AppCompatActivity;

import android.animation.ObjectAnimator;
import android.animation.ValueAnimator;
import android.os.Bundle;
import android.util.Log;
import android.view.View;

public class MainActivity extends AppCompatActivity {
    private ShapeView mShapeView;
    private static final String TAG = "wqq";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ProgressBar mProgressBar = findViewById(R.id.ProgressBar);
        mShapeView = findViewById(R.id.shapView);
        try {
            mProgressBar.setMax(4000);
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        }
        ValueAnimator animator = ObjectAnimator.ofFloat(0,4000);
        animator.setDuration(2000);
        animator.start();
        animator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator animation) {
                float progress = (float)animation.getAnimatedValue();
                try {
                    mProgressBar.setProgress((int)progress);
                } catch (IllegalArgumentException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    public void exchange(View view)
    {
        new Thread(new Runnable() {
            @Override
            public void run() {
                while (true) {
                    mShapeView.exchange();
                    Log.e(TAG, "run: wqq");
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }
}