android 自定义view仪表盘

package mda.jwipc.android.myas23;

import android.content.Context;
import android.graphics.*;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.View;

/**
 * Created by 10090 on 2020/11/20.
 */
public class DashBoard extends View {
    private float mAngle = 120; //未被画弧的角度。//如果改为0的话就是画的一个圆形。
    private Paint mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);//Paint.ANTI_ALIAS_FLAG防锯齿
    private float mRadius = Utils.dpToPx(150);//圆的半径
    private Path dash = new Path();//用来画刻度的path
    private PathDashPathEffect effect;//定义画可读的规则。
    private float copies = 20;//分成多少份？
    private float phase = 0;//从哪个位置开始画。
    private float mPointerLength = Utils.dpToPx(100);//指针的长度
    private int currentCopies = 2;//指针指向的当前刻度。

    {
        mPaint.setStyle(Paint.Style.STROKE);//  Paint.Style.STROKE 画线不填充。
        mPaint.setStrokeWidth(Utils.dpToPx(2));


        dash.addRect(0, 0, Utils.dpToPx(2), Utils.dpToPx(10), Path.Direction.CW);//这个Direction的方向要和圆弧的方向一致，否则坐标点就需要相反。 CW是顺时针，CCW是逆时针

        Path arc = new Path();//弧的路径。
        arc.addArc(getWidth() / 2 - mRadius, getHeight() / 2 - mRadius, getWidth() / 2 + mRadius, getHeight() / 2 + mRadius, 90 + mAngle / 2, 360 - mAngle);
        PathMeasure pathMeasure = new PathMeasure(arc, false);//测量弧的周长
        float length = pathMeasure.getLength();//弧的周长。
        //Utils.dpToPx(10)矩形的宽度， Utils.dpToPx(10)矩形的长度

        effect = new PathDashPathEffect(dash, (length - Utils.dpToPx(2)) / copies, phase, PathDashPathEffect.Style.ROTATE);
    }

    public DashBoard(Context context) {
        super(context);
    }

    public DashBoard(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public DashBoard(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        //useCenter 倒数第二个参数，是否用线连接圆心。 true连接起来，false不连接
        //360 - mAngle绘制路过的角度
        //90 + mAngle / 2起始角度。
        //left 矩形的左边坐标起点
        //top 矩形坐标的高度起点
        //right 矩形的右边结束坐标点
        //bottom 矩形结束的底部坐标点
        //画线
        canvas.drawArc(getWidth() / 2 - mRadius, getHeight() / 2 - mRadius, getWidth() / 2 + mRadius, getHeight() / 2 + mRadius, 90 + mAngle / 2, 360 - mAngle, false, mPaint);

        //画刻度
        mPaint.setPathEffect(effect);
        canvas.drawArc(getWidth() / 2 - mRadius, getHeight() / 2 - mRadius, getWidth() / 2 + mRadius, getHeight() / 2 + mRadius, 90 + mAngle / 2, 360 - mAngle, false, mPaint);
        mPaint.setPathEffect(null);

        //画指针
        canvas.drawLine(getWidth() / 2, getHeight() / 2,
                (float) (Math.cos(Math.toRadians(getAngleFromMark(currentCopies))) * mPointerLength + getWidth() / 2),
                (float) (Math.sin(Math.toRadians(getAngleFromMark(currentCopies))) * mPointerLength + getHeight() / 2),mPaint);
    }

    public void setRadius(float radius) {
        mRadius = Utils.dpToPx(radius);
        invalidate();
    }

    public void setCopies(float copies) {
        this.copies = copies;
        invalidate();
    }

    public void setCurrentCopies(int currentCopies){
        this.currentCopies = currentCopies;
        invalidate();
    }

    int getAngleFromMark(int mark) {
        return (int) (90 + mAngle / 2 + (360 - mAngle) / copies * mark);
    }
}

dp转Px

/**
 * Created by 10090 on 2020/11/20.
 */
public class Utils {

    public static float dpToPx(float dp){
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, Resources.getSystem().getDisplayMetrics());
    }
}