Android画个时钟玩玩

先看下最终的效果

开始实现

新建一个ClockView集成View

    public class ClockView extends View {
    
    }

先重写onMeasure方法，这里要先说一下View的测量模式，一共有三种：

• EXACTLY

  即精确值模式，当我们将控件的layout_width属性或layout_height属性指定为具体数值时，比如android:layout_width="100dp"，或者指定为math_parent属性时（占据父View的大小），系统使用的是EXACTLY模式。

• AT_MOST

  即最大值模式，当控件的layout_width属性或layout_height属性指定为wrap_content时，控件大小一般随着控件的子控件或内容的变化而变化，此时控件的尺寸只要不超过父控件允许的最大尺寸即可。

• UNSPECIFIED

  这个属性比较奇怪——它不指定其大小测量模式，View想多大就多大，通常情况下在绘制自定义View时才会使用。

  因为View的onMeasure方法只支持EXACTLY模式，当layout_width和layout_height为wrap_content时，View的大小就显得很奇怪了，如下图。

  

所以我们重写一下onMeasure方法可以指定View width、height的最小值

    /**
     * 当布局为wrap_content时设置默认长宽
     * @param widthMeasureSpec
     * @param heightMeasureSpec
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(measure(widthMeasureSpec), measure(heightMeasureSpec));
    }

    private int measure(int origin){
        int result = DEFAULT_MIN_WIDTH;
        int specMode = MeasureSpec.getMode(origin);
        int specSize = MeasureSpec.getSize(origin);
        if(specMode == MeasureSpec.EXACTLY){
            result = specSize;
        }else{
            if(specMode == MeasureSpec.AT_MOST){
                result = Math.min(result, specSize);
            }
        }
        return result;
    }

下面就是最重要的重写onDraw方法来绘制表盘、刻度、指针……，大致流程如下

• 画表盘，用drawCircle绘制一个圆作为表盘, 圆心坐标为(getWidth()/2, getHeight()/2)，半径为Math.min(getHeight()/2, getWidth()/2)。

//画外圆
float borderWidth = DEFAULT_BORDER_WIDTH;
Paint paintCircle = new Paint();
paintCircle.setStyle(Paint.Style.STROKE);
paintCircle.setAntiAlias(true);
paintCircle.setStrokeWidth(borderWidth);
canvas.drawCircle(getWidth() / 2, getHeight() / 2, Math.min(getHeight() / 2, getWidth() / 2) - borderWidth / 2, paintCircle);

• 画刻度线，在这里我们可以利用一个`canvas.rotate'方法就可以不用计算角度了

//画刻度线
float degreeLength = 0f;
Paint paintDegree = new Paint();
paintDegree.setAntiAlias(true);
for(int i=0;i<60;i++){
    if(i % 5 == 0){
        paintDegree.setStrokeWidth(6);
        degreeLength = DEFAULT_LONG_DEGREE_LENGTH;
    }else{
        paintDegree.setStrokeWidth(3);
        degreeLength = DEFAULT_SHORT_DEGREE_LENGTH;
    }
    canvas.drawLine(getWidth()/2, Math.abs(getWidth()/2 - getHeight()/2), getWidth()/2, Math.abs(getWidth()/2 - getHeight()/2) + degreeLength, paintDegree);
    canvas.rotate(360/60, getWidth()/2, getHeight()/2);
}

• 画刻度上的数字

//刻度数字
int degressNumberSize = 30;
canvas.translate(getWidth() / 2, getHeight() / 2);
Paint paintDegreeNumber = new Paint();
paintDegreeNumber.setTextAlign(Paint.Align.CENTER);
paintDegreeNumber.setTextSize(degressNumberSize);
paintDegreeNumber.setFakeBoldText(true);
for(int i=0;i<12;i++){
    float[] temp = calculatePoint((i+1)*30, r - DEFAULT_LONG_DEGREE_LENGTH - degressNumberSize/2 - 15);
    canvas.drawText((i+1)+"", temp[2], temp[3] + degressNumberSize/2-6, paintDegreeNumber);
}

/**
 * 根据角度和长度计算线段的起点和终点的坐标
 * @param angle
 * @param length
 * @return
 */
private float[] calculatePoint(float angle, float length){
    float[] points = new float[4];
    if(angle <= 90f){
        points[0] = -(float) Math.sin(angle*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[1] = (float) Math.cos(angle*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[2] = (float) Math.sin(angle*Math.PI/180) * length;
        points[3] = -(float) Math.cos(angle*Math.PI/180) * length;
    }else if(angle <= 180f){
        points[0] = -(float) Math.cos((angle-90)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[1] = -(float) Math.sin((angle-90)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[2] = (float) Math.cos((angle-90)*Math.PI/180) * length;
        points[3] = (float) Math.sin((angle-90)*Math.PI/180) * length;
    }else if(angle <= 270f){
        points[0] = (float) Math.sin((angle-180)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[1] = -(float) Math.cos((angle-180)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[2] = -(float) Math.sin((angle-180)*Math.PI/180) * length;
        points[3] = (float) Math.cos((angle-180)*Math.PI/180) * length;
    }else if(angle <= 360f){
        points[0] = (float) Math.cos((angle-270)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[1] = (float) Math.sin((angle-270)*Math.PI/180) * DEFAULT_POINT_BACK_LENGTH;
        points[2] = -(float) Math.cos((angle-270)*Math.PI/180) * length;
        points[3] = -(float) Math.sin((angle-270)*Math.PI/180) * length;
    }
    return points;
}

• 画指针

//画指针
Paint paintHour = new Paint();
paintHour.setAntiAlias(true);
paintHour.setStrokeWidth(15);
Paint paintMinute = new Paint();
paintMinute.setAntiAlias(true);
paintMinute.setStrokeWidth(10);
Paint paintSecond = new Paint();
paintSecond.setAntiAlias(true);
paintSecond.setStrokeWidth(5);
Calendar now = Calendar.getInstance();
float[] hourPoints = calculatePoint(now.get(Calendar.HOUR_OF_DAY)%12/12f*360, hourPointerLength);
canvas.drawLine(hourPoints[0], hourPoints[1], hourPoints[2], hourPoints[3], paintHour);
float[] minutePoints = calculatePoint(now.get(Calendar.MINUTE)/60f*360, minutePointerLength);
canvas.drawLine(minutePoints[0], minutePoints[1], minutePoints[2], minutePoints[3], paintMinute);
float[] secondPoints = calculatePoint(now.get(Calendar.SECOND)/60f*360, secondPointerLength);
canvas.drawLine(secondPoints[0], secondPoints[1], secondPoints[2], secondPoints[3], paintSecond);

• 画圆心

//画圆心
Paint paintCenter = new Paint();
paintCenter.setColor(Color.WHITE);
canvas.drawCircle(0, 0, 2, paintCenter);

最后只要启动一个无限循环的线程，每隔1秒针重绘一下View就能让指针动起来了

private Thread timeThread = new Thread() {
    @Override
    public void run() {
        try {
            while(true){
                updateHandler.sendEmptyMessage(0);
                Thread.sleep(1000);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
};

private Handler updateHandler = new Handler() {
    @Override
    public void handleMessage(Message msg) {
        invalidate();
    }
};

全部测试代码下载地址:

https://github.com/hellsam/clockdemo_android

欢迎留言交流，如有描述不当或错误的地方还请留言告知

本博客网址 hellsam.com