1.介绍

首先看下效果图

2.思路

1. 初始化一些参数
2. 绘制刻度盘
3. 绘制刻度盘下的圆弧
4. 绘制标题与温度标识
5. 绘制旋转按钮
6. 绘制温度
7. 处理滑动事件
8. 提供一些接口方法

3.实现

初始化一些参数

public class TempControlView extends View {

    // 控件宽
    private int width;
    // 控件高
    private int height;
    // 刻度盘半径
    private int dialRadius;
    // 圆弧半径
    private int arcRadius;
    // 刻度高
    private int scaleHeight = dp2px(10);
    // 刻度盘画笔
    private Paint dialPaint;
    // 圆弧画笔
    private Paint arcPaint;
    // 标题画笔
    private Paint titlePaint;
    // 温度标识画笔
    private Paint tempFlagPaint;
    // 旋转按钮画笔
    private Paint buttonPaint;
    // 温度显示画笔
    private Paint tempPaint;
    // 文本提示
    private String title = "最高温度设置";
    // 温度
    private int temperature;
    // 最低温度
    private int minTemp = 15;
    // 最高温度
    private int maxTemp = 30;
    // 四格（每格4.5度，共18度）代表温度1度
    private int angleRate = 4;
    // 按钮图片
    private Bitmap buttonImage = BitmapFactory.decodeResource(getResources(),
            R.mipmap.btn_rotate);
    // 按钮图片阴影
    private Bitmap buttonImageShadow = BitmapFactory.decodeResource(getResources(),
            R.mipmap.btn_rotate_shadow);
    // 抗锯齿
    private PaintFlagsDrawFilter paintFlagsDrawFilter;
    // 温度改变监听
    private OnTempChangeListener onTempChangeListener;

    // 以下为旋转按钮相关

    // 当前按钮旋转的角度
    private float rotateAngle;
    // 当前的角度
    private float currentAngle;

    ...
    
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        // 控件宽、高
        width = height = Math.min(h, w);
        // 刻度盘半径
        dialRadius = width / 2 - dp2px(20);
        // 圆弧半径
        arcRadius = dialRadius - dp2px(20);
    }

    ...
}

绘制刻度盘

以屏幕中心为画布原点，圆弧角度为270°，绘制未选中与选中状态的刻度盘。
旋转方法中多减的2°是后期调整所得，不用在意。

/**
 * 绘制刻度盘
 *
 * @param canvas 画布
 */
private void drawScale(Canvas canvas) {
    canvas.save();
    canvas.translate(getWidth() / 2, getHeight() / 2);
    // 逆时针旋转135-2度
    canvas.rotate(-133);
    dialPaint.setColor(Color.parseColor("#3CB7EA"));
    for (int i = 0; i < 60; i++) {
        canvas.drawLine(0, -dialRadius, 0, -dialRadius + scaleHeight, dialPaint);
        canvas.rotate(4.5f);
    }

    canvas.rotate(90);
    dialPaint.setColor(Color.parseColor("#E37364"));
    for (int i = 0; i < (temperature - minTemp) * angleRate; i++) {
        canvas.drawLine(0, -dialRadius, 0, -dialRadius + scaleHeight, dialPaint);
        canvas.rotate(4.5f);
    }
    canvas.restore();
}

绘制刻度盘下的圆弧

/**
 * 绘制刻度盘下的圆弧
 *
 * @param canvas 画布
 */
private void drawArc(Canvas canvas) {
    canvas.save();
    canvas.translate(getWidth() / 2, getHeight() / 2);
    canvas.rotate(135 + 2);
    RectF rectF = new RectF(-arcRadius, -arcRadius, arcRadius, arcRadius);
    canvas.drawArc(rectF, 0, 265, false, arcPaint);
    canvas.restore();
}

绘制标题与温度标识

    /**
     * 绘制标题与温度标识
     *
     * @param canvas 画布
     */
    private void drawText(Canvas canvas) {
        canvas.save();

        // 绘制标题
        float titleWidth = titlePaint.measureText(title);
        canvas.drawText(title, (width - titleWidth) / 2, dialRadius * 2 + dp2px(15), titlePaint);

        // 绘制最小温度标识
        // 最小温度如果小于10，显示为0x
        String minTempFlag = minTemp < 10 ? "0" + minTemp : minTemp + "";
        float tempFlagWidth = titlePaint.measureText(maxTemp + "");
        canvas.rotate(55, width / 2, height / 2);
        canvas.drawText(minTempFlag, (width - tempFlagWidth) / 2, height + dp2px(5), tempFlagPaint);

        // 绘制最大温度标识
        canvas.rotate(-105, width / 2, height / 2);
        canvas.drawText(maxTemp + "", (width - tempFlagWidth) / 2, height + dp2px(5), tempFlagPaint);
        canvas.restore();
    }

绘制旋转按钮

/**
 * 绘制旋转按钮
 *
 * @param canvas 画布
 */
private void drawButton(Canvas canvas) {
    // 按钮宽高
    int buttonWidth = buttonImage.getWidth();
    int buttonHeight = buttonImage.getHeight();
    // 按钮阴影宽高
    int buttonShadowWidth = buttonImageShadow.getWidth();
    int buttonShadowHeight = buttonImageShadow.getHeight();

    // 绘制按钮阴影
    canvas.drawBitmap(buttonImageShadow, (width - buttonShadowWidth) / 2,
            (height - buttonShadowHeight) / 2, buttonPaint);

    Matrix matrix = new Matrix();
    // 设置按钮位置
    matrix.setTranslate(buttonWidth / 2, buttonHeight / 2);
    // 设置旋转角度
    matrix.preRotate(45 + rotateAngle);
    // 按钮位置还原，此时按钮位置在左上角
    matrix.preTranslate(-buttonWidth / 2, -buttonHeight / 2);
    // 将按钮移到中心位置
    matrix.postTranslate((width - buttonWidth) / 2, (height - buttonHeight) / 2);

    //设置抗锯齿
    canvas.setDrawFilter(paintFlagsDrawFilter);
    canvas.drawBitmap(buttonImage, matrix, buttonPaint);
}

绘制温度

/**
 * 绘制温度
 *
 * @param canvas 画布
 */
private void drawTemp(Canvas canvas) {
    canvas.save();
    canvas.translate(getWidth() / 2, getHeight() / 2);

    float tempWidth = tempPaint.measureText(temperature + "");
    float tempHeight = (tempPaint.ascent() + tempPaint.descent()) / 2;
    canvas.drawText(temperature + "°", -tempWidth / 2 - dp2px(5), -tempHeight, tempPaint);
    canvas.restore();
}

处理滑动事件

private boolean isDown;
private boolean isMove;

@Override
public boolean onTouchEvent(MotionEvent event) {
    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:
            isDown = true;
            float downX = event.getX();
            float downY = event.getY();
            currentAngle = calcAngle(downX, downY);
            break;

        case MotionEvent.ACTION_MOVE:
            isMove = true;
            float targetX;
            float targetY;
            downX = targetX = event.getX();
            downY = targetY = event.getY();
            float angle = calcAngle(targetX, targetY);

            // 滑过的角度增量
            float angleIncreased = angle - currentAngle;

            // 防止越界
            if (angleIncreased < -270) {
                angleIncreased = angleIncreased + 360;
            } else if (angleIncreased > 270) {
                angleIncreased = angleIncreased - 360;
            }

            IncreaseAngle(angleIncreased);
            currentAngle = angle;
            invalidate();
            break;

        case MotionEvent.ACTION_CANCEL:
        case MotionEvent.ACTION_UP: {
            if (isDown && isMove) {
                // 纠正指针位置
                rotateAngle = (float) ((temperature - minTemp) * angleRate * 4.5);
                invalidate();
                // 回调温度改变监听
                onTempChangeListener.change(temperature);
                isDown = false;
                isMove = false;
            }
            break;
        }
    }
    return true;
}

/**
 * 以按钮圆心为坐标圆点，建立坐标系，求出(targetX, targetY)坐标与x轴的夹角
 *
 * @param targetX x坐标
 * @param targetY y坐标
 * @return (targetX, targetY)坐标与x轴的夹角
 */
private float calcAngle(float targetX, float targetY) {
    float x = targetX - width / 2;
    float y = targetY - height / 2;
    double radian;

    if (x != 0) {
        float tan = Math.abs(y / x);
        if (x > 0) {
            if (y >= 0) {
                radian = Math.atan(tan);
            } else {
                radian = 2 * Math.PI - Math.atan(tan);
            }
        } else {
            if (y >= 0) {
                radian = Math.PI - Math.atan(tan);
            } else {
                radian = Math.PI + Math.atan(tan);
            }
        }
    } else {
        if (y > 0) {
            radian = Math.PI / 2;
        } else {
            radian = -Math.PI / 2;
        }
    }
    return (float) ((radian * 180) / Math.PI);
}

/**
 * 增加旋转角度
 *
 * @param angle 增加的角度
 */
private void IncreaseAngle(float angle) {
    rotateAngle += angle;
    if (rotateAngle < 0) {
        rotateAngle = 0;
    } else if (rotateAngle > 270) {
        rotateAngle = 270;
    }
    temperature = (int) (rotateAngle / 4.5) / angleRate + minTemp;
}

提供一些接口方法

/**
 * 设置温度
 *
 * @param minTemp 最小温度
 * @param maxTemp 最大温度
 * @param temp    设置的温度
 */
public void setTemp(int minTemp, int maxTemp, int temp) {
    this.minTemp = minTemp;
    this.maxTemp = maxTemp;
    this.temperature = temp;
    this.angleRate = 60 / (maxTemp - minTemp);
    rotateAngle = (float) ((temp - minTemp) * angleRate * 4.5);
    invalidate();
}

/**
 * 设置温度改变监听
 *
 * @param onTempChangeListener 监听接口
 */
public void setOnTempChangeListener(OnTempChangeListener onTempChangeListener) {
    this.onTempChangeListener = onTempChangeListener;
}

/**
 * 温度改变监听接口
 */
public interface OnTempChangeListener {
    /**
     * 回调方法
     *
     * @param temp 温度
     */
    void change(int temp);
}

4.写在最后

源码已托管到GitHub上，欢迎Fork，觉得还不错就Start一下吧！

点击下载源码

GitHub地址：https://github.com/alidili/TempControlView

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