Android绘图canvas 圆周运动两种实现方式

圆周运动两种实现方式"/>

Android绘图canvas 圆周运动两种实现方式

Android最近在自定义view，需要做一个圆周运动；

1. 方案一：首先想到的是根据圆的方程，实时递增x值进行，然后实时计算y值，代码如下：

package com.example.demo.practice.ui;import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;import com.example.demo.practice.dashboardview.PxUtils;
import com.example.demo.practice.tool.TimeAction;/*** Created by hanbo on 2018-01-23.*/public class SatelliteView extends View {private int mWidth;private int mHeight;private Paint p;private float degree;private Context context;private TimeAction timeAction;//运动圆的轨迹private int x;private int y;//圆心坐标private int x1;private int y1;//最大半径private int r1;//r平方private int r_pow;//上下半圆private boolean flag;private int left;private int right;private int speed=4;private Handler handler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);if (flag) {if (x + speed >= right) {flag = false;}x = x + speed;y = (int) (y1 - Math.sqrt(r_pow - (x - x1) * (x - x1)));} else {if (x - speed <= left) {flag = true;}x = x - speed;y = (int) (y1 + Math.sqrt(r_pow - (x - x1) * (x - x1)));}invalidate();}};public SatelliteView(Context context, AttributeSet attrs) {super(context, attrs);this.context = context;p = new Paint();p.setAntiAlias(true);degree = 0;timeAction = new TimeAction(handler, 100);timeAction.start();}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {int widthSize = MeasureSpec.getSize(widthMeasureSpec);int widthMode = MeasureSpec.getMode(widthMeasureSpec);int heightSize = MeasureSpec.getSize(heightMeasureSpec);int heightMode = MeasureSpec.getMode(heightMeasureSpec);if (widthMode == MeasureSpec.EXACTLY) {mWidth = widthSize;} else {mWidth = PxUtils.dpToPx(200, context);}if (heightMode == MeasureSpec.EXACTLY) {mHeight = heightSize;} else {mHeight = PxUtils.dpToPx(200, context);}setMeasuredDimension(mWidth, mHeight);r1 = mWidth;if (mHeight < mWidth) {r1 = mHeight;}x = mWidth / 2;x1 = x;y1 = mHeight / 2;y = y1 - r1 / 4;left = x1 - r1 / 4;right = x1 + r1 / 4;r_pow = r1 * r1 / 16;}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);p.setColor(Color.parseColor("#00a1e9"));p.setStrokeWidth(5);p.setStyle(Paint.Style.STROKE);canvas.drawCircle(x1, y1, r1 / 4, p);p.setColor(Color.parseColor("#194464"));canvas.drawCircle(x1, y1, r1 * 3 / 8, p);p.setStyle(Paint.Style.FILL);p.setColor(Color.parseColor("#00a1e9"));canvas.drawCircle(x, y, 10, p);}@Overrideprotected void onDetachedFromWindow() {timeAction.stop();super.onDetachedFromWindow();}
}

这种方式的缺点很明显，就是速度不均匀，y与x变化率不同。

方案二：以角度计算xy的值，这样的速度就比较均匀了，代码如下：

package com.example.demo.practice.ui;import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.view.View;import com.example.demo.practice.dashboardview.PxUtils;
import com.example.demo.practice.tool.TimeAction;/*** Created by hanbo on 2018-01-23.*/public class SatelliteView extends View {private static String TAG = "卫星图";private int mWidth;private int mHeight;private Paint p;private Context context;//定时器private TimeAction timeAction;//运动圆的轨迹private int x;private int y;//圆心坐标private int x1;private int y1;//最大半径private int r1;//r平方private int r_run;//速度private double speed = 0.04;private double degree;private Handler handler = new Handler() {@Overridepublic void handleMessage(Message msg) {super.handleMessage(msg);degree=speed+degree;if (degree >= 360) {degree = degree - 360;}y = (int) (y1 - r_run * Math.cos(degree));x = (int) (x1 + r_run * Math.sin(degree));invalidate();}};public SatelliteView(Context context, AttributeSet attrs) {super(context, attrs);this.context = context;p = new Paint();p.setAntiAlias(true);degree = 0;timeAction = new TimeAction(handler, 100);timeAction.start();}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {int widthSize = MeasureSpec.getSize(widthMeasureSpec);int widthMode = MeasureSpec.getMode(widthMeasureSpec);int heightSize = MeasureSpec.getSize(heightMeasureSpec);int heightMode = MeasureSpec.getMode(heightMeasureSpec);if (widthMode == MeasureSpec.EXACTLY) {mWidth = widthSize;} else {mWidth = PxUtils.dpToPx(200, context);}if (heightMode == MeasureSpec.EXACTLY) {mHeight = heightSize;} else {mHeight = PxUtils.dpToPx(200, context);}setMeasuredDimension(mWidth, mHeight);r1 = mWidth;if (mHeight < mWidth) {r1 = mHeight;}r_run = r1 / 4;x = mWidth / 2;x1 = x;y1 = mHeight / 2;y = y1 - r_run;}@Overrideprotected void onDraw(Canvas canvas) {super.onDraw(canvas);p.setColor(Color.parseColor("#00a1e9"));p.setStrokeWidth(5);p.setStyle(Paint.Style.STROKE);canvas.drawCircle(x1, y1, r1 / 4, p);p.setColor(Color.parseColor("#194464"));canvas.drawCircle(x1, y1, r1 * 3 / 8, p);p.setStyle(Paint.Style.FILL);p.setColor(Color.parseColor("#00a1e9"));canvas.drawCircle(x, y, 10, p);}@Overrideprotected void onDetachedFromWindow() {timeAction.stop();super.onDetachedFromWindow();}
}